elevated atmospheric carbon dioxide effects on soybean and ... · s. a. prior,* g. b. runion, h. h....

TECHNICAL REPORTS

TECHNICAL REPORTS PLANT AND ENVIRONMENT INTERACTIONS

Elevated Atmospheric Carbon Dioxide Effects on Soybean and Sorghum Gas Exchange

in Conventional and No-Tillage Systems

S A Prior G B Runion H H Rogers and F J Arriaga USDAndashARS

Increasing atmospheric CO2 concentration has led to concerns

about potential effects on production agriculture In the fall of 1997 a study was initiated to compare the response of two crop management systems (conventional tillage and no-tillage) to elevated CO

2 The study used a split-plot design

replicated three times with two management systems as main plots and two atmospheric CO

2 levels (ambient and twice

ambient) as split plots using open-top chambers on a Decatur silt loam soil (clayey kaolinitic thermic Rhodic Paleudults) The conventional system was a grain sorghum [Sorghum bicolor (L) Moench] and soybean [Glycine max (L) Merr] rotation with winter fallow and spring tillage practices In the no-tillage system sorghum and soybean were rotated and three cover crops were used [crimson clover (Trifolium incarnatum L) sunn hemp (Crotalaria juncea L) and wheat (Triticum aestivum L)] Over multiple growing seasons the effect of management and CO

2 concentration on leaf-level

gas exchange during row crop (soybean in 1999 2001 and 2003 sorghum in 2000 2002 and 2004) reproductive growth were evaluated Treatment effects were fairly consistent across years In general higher photosynthetic rates were observed under CO

2 enrichment (more so with soybean) regardless of

residue management practice Elevated CO2 led to decreases

in stomatal conductance and transpiration which resulted in increased water use effi ciency Th e effects of management system on gas exchange measurements were infrequently significant as were interactions of CO

2 and management

These results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO

2ndashenriched environments during reproductive growth

Copyright copy 2010 by the American Society of Agronomy Crop Science

Society of America and Soil Science Society of America All rights

reserved No part of this periodical may be reproduced or transmitted

in any form or by any means electronic or mechanical including phoshy

tocopying recording or any information storage and retrieval system

without permission in writing from the publisher

Published in J Environ Qual 39596ndash608 (2010)

doi102134jeq20090181

Published online 1 Feb 2010

Received 13 May 2009

Corresponding author (stevepriorarsusdagov)

copy ASA CSSA SSSA

677 S Segoe Rd Madison WI 53711 USA

For over yr intense row crop agriculture has been pracshy

ticed in the southeastern United States These practices (ie

inversion tillage with fallow winter periods) have left the soil relashy

tively infertile highly eroded and low in organic matter (Carreker

et al 1977) Crops in the southeast are often subjected to periods

of water deficit during times of high demand such as reproducshy

tive growth The use of conservation practices that include less

tillage and the use of cover crops can help counter the soil degshy

radation caused by years of intense agriculture Th ese practices

enhance soil C storage and improve soil physical properties that

can reduce erosion and increase plant-available water (Phillips et

al 1980 Gebhardt et al 1985 Kern and Johnson 1993 Hunt

et al 1996 Diaz-Zorita et al 2002 Triplett and Dick 2008)

Additional water can become available to plants in conservation

systems when plant residue left on the soil surface serves as mulch

and reduces evaporative losses (Reicosky et al 1999) Within the

last two decades the adoption of conservation tillage systems has

dramatically increased (CTIC 2004)

In addition to alterations in management practices the environshy

ment is also changing Atmospheric CO2 concentration is rising at

an unprecedented rate caused by fossil fuel burning and land use

change (Keeling and Whorf 2001) Increasing atmospheric CO2

concentration has led to concerns about its potential eff ects on

production agriculture Elevated CO2 has the potential to enhance

crop system processes such as photosynthesis and plant water use

efficiency (WUE) leading to increased biomass production (Rogers

et al 1983b Amthor 1995 Kimball et al 2002) As with conshy

servation systems elevated CO2 can improve soil quality through

the addition of organic residue above and below ground (Rogers

et al 1999 Torbert et al 2000 Prior et al 2003) This also has

the ability to help mitigate global climate change by sequestering

atmospheric CO2 in plant and soil systems

Long-term CO2 studies evaluating C

3 and C

4 crops grown under

the same experimental conditions are lacking Although both of

these photosynthetic types benefit from increased WUE they are

known to respond differently to elevated CO2 with regard to carbon

metabolism (Rogers et al 1983b Amthor 1995) Th is diff erence

USDA-ARS National Soil Dynamics Lab 411 South Donahue Dr Auburn AL 36832

Names are necessary to report factually on available data however USDA does not

guarantee or warrant the standard of the production The use of the name by the

USDA implies no approval of the product to the exclusion of others that may be

suitable Assigned to Associate Editor Pierre-Andre Jacinthe

Abbreviations CT conventional tillage DOY day of year gs conductance NT no-till

P n photosynthesis Tr transpiration WUE water use effi ciency

596

in response could become important with regard to future manshy

agement decisions There have been no long-term studies comshy

paring conventional tillage (CT) with conservation tillage or

no-tillage (NT) systems under varying levels of atmospheric CO2

The objective of the current study was to examine the interactive

effects of management (CT and NT) and atmospheric CO2 conshy

centration (ambient and twice ambient) on leaf-level gas exchange

during row crop (soybean a N-fi xing C3 crop and grain sorghum

a C4 crop) reproductive growth over multiple seasons

Materials and Methods This study was conducted on an outdoor soil bin (7 m by 76

m) at the USDAndashARS National Soil Dynamics Laboratory in

Auburn Alabama (326deg N 855deg W) The bin was fi lled with

a Decatur silt loam soil (clayey kaolinitic thermic Rhodic

Paleudults) (Batchelor 1984) Open-top chambers comprised

of a structural aluminum frame (3 m in diameter by 24 m in

height) covered with a 02-mm PVC film panel (Rogers et al

1983a) were used for CO2 exposure Carbon dioxide was supshy

plied from a 127-Mg liquid CO2 receiver through a high-volume

dispensing manifold and the atmospheric CO2 concentration

was elevated by continuous injection of CO2 into plenum boxes

Air was introduced into each chamber through the bottom half

of each chamber cover which was double-walled the inside wall

was perforated with 25-cm-diameter holes to serve as ducts to

distribute air uniformly into the chamber Three chamber volshy

umes were exchanged every minute Carbon dioxide concentrashy

tions were continually monitored (24 h dminus1) using a time-shared

manifold with samples drawn through solenoids to an infrared

CO2 analyzer (Model 6252 LI-COR Inc Lincoln NE) Th e

target concentration for the elevated CO2 treatment was twice

ambient (~720 μL Lminus1) The mean (plusmn SE) daytime CO2 concenshy

trations across the six growing seasons of the study were 36635

plusmn 007 and 69180 plusmn 031 for the ambient and elevated CO2

treatments respectively (n = 58230) Plot locations were permashy

nently delineated using an anchored structural aluminum ring

(3 m in diameter) as a precaution to prevent lateral surface fl ow

of water into or out of plots

Two crop management systems (CT and NT) were estabshy

lished in the fall of 1997 In the CT system grain sorghum

[Sorghum bicolor (L) Moench lsquoPioneer 8282rsquo] and soybean

[Glycine max (L) Merr lsquoAsgrow 6101rsquo] were rotated each year

with spring tillage after winter fallow The NT system also used

a grain sorghum and soybean rotation with three cover crops

[crimson clover (Trifolium incarnatum L lsquoAU Robinrsquo) sunn

hemp (Crotalaria juncea L lsquoTropic Sunnrsquo) and wheat (Triticum aestivum L lsquoPioneer 2684rsquo)] grown using no-tillage practices In

both management systems row crop seeds were sown (20 per

meter of row) on 038-m row spacings Planting dates for soyshy

bean were 19 23 and 27 May for 1999 2001 and 2003 respecshy

tively dates for sorghum were 2 6 and 12 May for 2000 2002

and 2004 respectively Extension recommendations were used

in managing the crops fertilizer rates were based on standard soil

tests guidelines as recommended by the Auburn University Soil

Testing Laboratory (Adams et al 1994) Soybeans were grown

with no nitrogen fertilization but seeds were inoculated with

commercial Rhizobium (Nitragin Co Milwaukee WI) before

planting For grain sorghum fertilizer N (ammonium nitrate)

was hand-broadcast at a rate of 34 kg N haminus1 shortly after plantshy

ing and an additional 101 kg N haminus1 was similarly applied 30

d after planting Cover crops and sorghum (regrowth prevenshy

tion) were terminated with glyphosate (N-[phosphonomethyl]

glycine) 10 d before planting the following crop All crops were

harvested using standard procedures yield and biomass were

recorded as described in detail by Prior et al (2005) Harvest

dates for soybean were 25 22 and 20 October for 1999 2001

and 2003 respectively dates for sorghum were 14 14 and 17

August for 2000 2002 and 2004 respectively After harvest all

remaining residues were uniformly spread over their respective

study plot All operations described above were also conducted

on nonexperimental areas to ensure uniform treatment of areas

bordering the study plots

During reproductive growth for 6 yr leaf level measureshy

ments of photosynthesis (P n) stomatal conductance (g

s) and

transpiration (Tr) were made twice weekly using a LI-6400

Portable Photosynthesis System (LI-COR Inc Lincoln NE)

for soybean (C3 photosynthesis) and grain sorghum (C

4 phoshy

tosynthesis) Visual assessments of approximate growth stage

were also conducted during this period for soybean (Ritchie

et al 1992) and sorghum (Vanderlip 1979) Gas exchange

measurements were taken at midday on leaves (fully expanded

sun-exposed leaves at the canopy top) from three randomly

selected plants per plot and were initiated at the start of reproshy

ductive growth Water use effi ciency (μmol CO2 mmolminus1 H

2O)

was calculated by dividing P n by Tr (ie μmol CO

2 mminus2 sminus1

mmol H2O mminus2 sminus1) Rainfall was recorded on site throughout

each sampling period (Table 1)

The experiment was conducted using a split-plot design with

three replicate blocks Whole-plot treatments (tillage system)

were randomly assigned to half of each block Split-plot treatshy

ments (CO2 levels) were randomly assigned to two chambers

(3 m in diameter) within each whole plot There were a total of

12 chamber plot locations six were ambient CO2 treatments

(three for CT and three for NT) and six were elevated CO2

treatments (three for CT and three for NT) Data from each

chamber were averaged before statistical analysis Statistical

analyses of data were performed using the Mixed procedure of

the Statistical Analysis System (Littell et al 1996) A signifi shy

cance level of P le 010 was established a priori

Results

Soybean In 1999 elevated CO

2 signifi cantly increased P

n on 17 of 21

sampling dates (Table 2 Fig 1a) Days without a signifi cant

CO2 effect tended to occur later in the growing season when

Table 1 Rainfall recorded on site during each sampling period (the growshying season and sampling period for soybean is longer than for sorghum)

Species Year Rainfall No of events No gt10 mm

mm

Soybean 1999 16129 14 5

2001 15621 15 5

2003 26162 18 9

Sorghum 2000 8890 9 3

2002 6731 7 3

2004 18415 9 5

Prior et al Elevated CO2 Effects on Crop Gas Exchange 597

Table 2 Statistics (Pr gt F italics represent significance) for carbon dioxide concentration tillage system and their interaction on soybean gas exchange variables for the various sampling dates in 1999

Gas exchange variable

DOYdagger P n

gs

Tr WUE

CO Till C times T CO Till C times T CO Till C times T CO Till C times T 2 2 2 2

196 0007 0578 0482 0507 0688 0611 0331 0910 0486 lt0001 0372 0711

200 0002 0720 0602 0007 0805 0239 0015 0584 0171 lt0001 0761 0004

202 lt0001 0692 0258 0007 0777 0394 0021 0364 0868 lt0001 0440 0874

207 0006 0880 0494 0356 0441 0990 0270 0612 0951 0007 0514 0976

210 0006 0168 0606 0633 0192 0820 0861 0170 0974 0003 0511 0287

214 0003 0158 0310 0430 0202 0386 0426 0192 0157 0005 0142 0052

218 0001 0353 0013 0781 0120 0058 0958 0372 0080 lt0001 0434 0107

221 0009 0165 0724 0339 0246 0418 0515 0227 0748 0002 0613 0825

224 0022 0257 0739 0813 0560 0600 0477 0763 0662 0004 0126 0223

228 0012 0220 0641 0545 0326 0522 0844 0398 0518 lt0001 0737 0958

231 0163 0242 0506 0420 0950 0498 0604 0607 0728 0013 0258 0185

238 lt0001 0309 0025 0098 0455 0241 0284 0110 0172 0001 0748 0935

242 lt0001 0156 0102 0005 0117 0017 0036 0312 0055 0001 0785 0956

246 0005 0367 0625 0085 0657 0610 0055 0653 0517 lt0001 0633 0384

250 0015 0766 0718 0109 0650 0610 0130 0297 0643 0003 0112 0682

253 0122 0876 0730 0050 0618 0737 0013 0977 0706 lt0001 0794 0976

257 0018 0324 0008 0010 0634 0021 0008 0899 0012 0003 0702 0883

260 0051 0283 0728 0213 0466 0948 0257 0280 0926 0004 0710 0929

264 0406 0837 0206 0021 0119 0126 0016 0306 0099 0003 0530 0545

267 0023 0854 0660 0412 0699 0536 0448 0706 0683 lt0001 0081 0555

273 0573 0979 0696 0006 0442 0712 0008 0577 0802 lt0001 0184 0422

Avg lt0001 0324 0620 0002 0649 0474 0005 0861 0400 lt0001 0125 0148

dagger C times T interaction between carbon dioxide concentration and tillage system CO2 carbon dioxide concentration DOY day of year g

s conductance (mol H

2O

mminus2 sminus1) P photosynthesis (μmol CO mminus2 sminus1) Till tillage system Tr transpiration (mmol H O mminus2 sminus1) WUE water use effi ciency (μmol CO mmolminus1 H O) n 2 2 2 2

plants were becoming senescent There were no signifi cant

effects of tillage on P n (Table 2) Signifi cant interactions of CO

2

and tillage were noted only on three dates (Table 2) Early in the

season (day of year [DOY] 218) CO2 increased P

n under NT

conditions However later in the season (DOY 238 and 257)

this condition was reversed in that CO2 increased P

n under CT

The 2001 growing season was similar to 1999 in that elevated

CO2 signifi cantly increased P

n on 17 of 22 sampling dates (Table

3 Fig 2a) Again days with no CO2 effect tended to occur later

in the growing season Also similar to 1999 there tended to be

no main effects of tillage on P n with the exception of DOY 262

(Table 3) when NT reduced P n Significant interactions of CO

2

and tillage were noted only on two dates (DOY 226 and 236

Table 3) These interactions were similar to that which occurred

early in 1999 in that elevated CO2 increased P

n under NT

In 2003 elevated CO2 signifi cantly increased P

n on 17 of 19

sampling dates (Table 4 Fig 3a) As in the prior two seasons

days with no CO2 effects occurred late in the season Again

tillage tended to have no signifi cant eff ect on P n exceptions

were noted on DOY 220 234 241 and 255 (Table 4) On the

fi rst two of these dates NT increased P n whereas on the latter

two dates NT signifi cantly reduced P n Interactions of CO

2

with tillage were noted on two dates (Table 4) As in 1999 on

the early date (DOY 213) elevated CO2 increased P

n under

NT However later in the season (DOY 255) elevated CO2

increased P under CT n

Elevated CO2 significantly increased seasonal averages for P

n

in each of the 3 yr (Tables 2ndash4 Fig 1ndash3) and when averaged

across all three seasons (P lt 0001) These seasonal and total avershy

ages reflected no main effect of tillage (total average P = 0794)

or interaction between CO2 and tillage (total average P = 0903)

In 1999 gs was signifi cantly lower in the elevated CO

2 treatshy

ment on 9 of 21 sampling dates (Table 2 Fig 1b) Th ere were

no main effects of tillage on gs (Table 2) Signifi cant interactions

of CO2 and tillage were noted only on DOY 218 242 and 257

(Table 2) On DOY 218 under ambient CO2 g

s was signifi cantly

lower under NT compared with CT On the latter two dates

elevated CO2 significantly reduced g

s only in the NT treatment

Th e eff ect of CO2 on g

s in 2001 was similar to 1999 in that

elevated CO2 signifi cantly reduced g

s on 10 of 22 sampling

dates (Table 3 Fig 2b) Also similar to 1999 there tended to

be no main effects of tillage on gs with exceptions on DOY

198 220 and 226 (Table 3) On the fi rst date gs was signifi shy

cantly reduced under NT whereas on the latter two dates NT

signifi cantly increased gs Significant interactions of CO

2 and

tillage were noted on DOY 215 220 and 243 (Table 3) Th e

first two dates were similar to that which occurred early in

1999 in that elevated CO2 signifi cantly reduced g

s in the NT

treatment However on DOY 243 this condition was reversed

in that elevated CO2 signifi cantly reduced g

s under CT

In 2003 elevated CO2 signifi cantly reduced g

s on 10 of

19 sampling dates (Table 4 Fig 3b) A tillage eff ect on gs was

noted only on DOY 241 and 255 (Table 4) in both cases

NT signifi cantly reduced gs In 2003 there were no signifi cant

interactions between CO2 and tillage on g

s (Table 4)

Elevated CO2 significantly reduced seasonal averages of g

s in

each of the 3 yr and when averaged across all three seasons (P lt 0001) These seasonal (Tables 2ndash4 Fig 1ndash3) and total aver-

Journal of Environmental Quality bull Volume 39 bull MarchndashApril 2010 598

Fig 1 Soybean gas exchange measures taken during reproductive growth in 1999 (a) Photosynthesis (P

n) (b) Stomatal conductance (g

s) (c) Transpiration (Tr) and (d) Water use effi ciency (WUE) Soybean

was grown under conventional tillage (CT) or no-tillage (NT) and exposed to ambient (A) or elevated (E) atmospheric CO

2 Asterisks indicate dates with a signifi cant CO

2 eff ect (P le 010) Values within graphs

are seasonal averages averages followed by different letters were signifi cantly diff erent (LSMeans procedure Proc Mixed SAS P le 010 n = 3) Growth stages are noted at the top of the fi gure R1 (beginning bloom) R3 (beginning pod) R4 (full pod) R5 (beginning seed) R6 (full seed) and R7 (beginshyning maturity)

ages refl ected no main effect of tillage

(total average P = 0868) or interacshy

tion between CO2 and tillage (total

average P = 0821)

In 1999 elevated CO2 signifi shy

cantly reduced Tr on 8 of 21 sampling

dates (Table 2 Fig 1c) There were no

main effects of tillage on Tr (Table 2)

Significant interactions of CO2 and

tillage were noted on DOY 218 242

257 and 264 (Table 2) On DOY

218 under ambient CO2 Tr was sigshy

nificantly lower under NT compared

with CT On the remaining dates

elevated CO2 signifi cantly reduced Tr

only in the NT treatment

Th e eff ect of CO2 on Tr in 2001 was

similar to 1999 in that elevated CO2

significantly reduced Tr on 9 of 22

sampling dates (Table 3 Fig 2c) Also

similar to 1999 there tended to be no

main effects of tillage on Tr with excepshy

tions on DOY 198 and 220 (Table 3)

when NT significantly reduced Tr on

the first date but signifi cantly increased

Tr on the second Signifi cant interacshy

tions of CO2 and tillage were noted

on DOY 215 and 220 (Table 3) as in

1999 elevated CO2 reduced Tr only in

the NT treatment



dates (Table 4 Fig 3c) Although tillshy

age effects remained infrequent sigshy

nifi cant effects were noted on DOY

234 241 and 255 (Table 4) On the

fi rst date NT increased Tr whereas it

was reduced in this treatment on the

latter two dates In 2003 a signifi cant

interaction between CO2 and tillage

was noted only on DOY 255 (Table

4) as in other years elevated CO2

reduced Tr only under NT

Elevated CO2 signifi cantly reduced

seasonal averages for Tr in each of the

3 yr (Tables 2ndash4 Fig 1ndash3) and when

averaged across all three seasons (P lt

0001) These seasonal and total avershy




average P = 0611)

Water use efficiency was the most

consistent variable measured in

1999 this measure was signifi cantly

increased by elevated CO2 on all dates

(Table 2 Fig 1d) A main effect of tillshy

age on WUE was noted on DOY 267

(Table 2) when WUE was increased




DOYdagger P n

gs

Tr WUE


198 0092 0222 0765 0231 0091 0884 0169 0066 0784 lt0001 0119 0335

200 0008 0386 0397 0383 0355 0412 0348 0429 0145 0002 0567 0334

205 lt0001 0920 0867 0001 0595 0654 0002 0993 0787 0005 0993 0918

208 lt0001 0248 0105 0089 0674 0682 0280 0480 0632 lt0001 0060 0284

212 lt0001 0605 0944 0312 0678 0890 0551 0702 0941 lt0001 0813 0541

215 0130 0757 0129 0107 0944 0042 0022 0680 0029 0008 0325 0353

220 0003 0146 0320 0012 0012 0007 0139 0061 0051 0006 0738 0256

222 0094 0533 0724 0024 0353 0386 0018 0326 0402 lt0001 0256 0563

226 lt0001 0231 0002 lt0001 0003 0630 0001 0195 0421 lt0001 0535 0233

229 0008 0664 0929 0002 0390 0468 0024 0818 0567 lt0001 0727 0288

233 0006 0985 0365 0615 0853 0445 0871 0844 0526 0009 0520 0386

236 0002 0349 0009 0916 0718 0186 0711 0597 0206 0001 0830 0088

240 0177 0249 0103 lt0001 0902 0127 lt0001 0484 0255 lt0001 0636 0652

243 0041 0943 0636 0607 0644 0044 0575 0601 0114 0003 0092 0035

247 0018 0468 0270 0001 0529 0236 0003 0366 0237 lt0001 0338 0466

249 0012 0944 0111 0538 0324 0161 0748 0529 0196 0001 0505 0940

255 0015 0583 0627 0035 0598 0712 0023 0385 0924 lt0001 0746 0987

257 0013 0412 0519 0757 0240 0761 0752 0454 0458 0001 0423 0707

262 0835 0048 0859 0080 0116 0675 0078 0105 0957 0002 0540 0124

264 0031 0640 0451 0683 0669 0469 0798 0626 0481 lt0001 0611 0218

268 0254 0945 0458 0192 0750 0449 0217 0813 0525 0002 0931 0654

270 0638 0601 0136 0682 0419 0234 0703 0348 0258 lt0001 0157 0006

Avg lt0001 0849 0797 lt0001 0613 0987 0002 0959 0981 lt0001 0555 0081



2O


under NT Significant interactions of CO2 and tillage occurred (P = 0003) elevated CO

2 increased WUE in both tillage treat-

on DOY 200 and 214 (Table 2) On the first date elevated ments with a greater magnitude of response under NT

CO2 increased WUE in both tillage treatments with the magshy

nitude being greater under NT On the latter date elevated Sorghum CO

2 increased WUE only under NT In 2000 elevated CO


n on 6 of 13

In 2001 WUE was similar to 1999 in that elevated CO2 sig- sampling dates (Table 5 Fig 4a) Main effects of tillage were

nificantly increased WUE on all dates (Table 3 Fig 2d) Main noted on five dates (Table 5) No-till increased P on DOY 217 n

eff ects of tillage on WUE were observed on DOY 208 and 243 but reduced it on DOY 189 193 201 and 220 There was a (Table 3) when WUE under NT was increased on the fi rst date significant interaction of CO and tillage on DOY 209 (Table

2

and reduced on the second Signifi cant interactions of CO and 5) when elevated CO increased P only under CT 2 2 n

tillage were noted on DOY 236 243 and 270 (Table 3) On The 2002 growing season was similar to 2000 in that eleshythe first date elevated CO increased WUE in both tillage treat- vated CO signifi cantly increased P only on three of nine samshy2 2 n

ments with a greater magnitude of response under NT On the pling dates (Table 6 Fig 5a) There were no main eff ects of second date elevated CO

2 increased WUE only under CT On tillage on P

n (Table 6) A significant interaction of CO

2 with

the third date elevated CO2 increased WUE only under NT tillage occurred on DOY 210 (Table 6) under elevated CO

2

In 2003 elevated CO2 significantly increased WUE on all P

n was significantly higher under NT compared with CT

dates (Table 4 Fig 3d) There was a main effect of tillage only In contrast to the previous two seasons elevated CO2 signifshy

on DOY 259 (Table 4) when NT increased WUE Signifi cant icantly increased P n on 8 of 10 sampling dates in 2004 (Table 7

interactions of CO2 and tillage occurred on DOY 225 232 Fig 6a) No-till signifi cantly reduced P

n on DOY 212 and 217

and 259 (Table 4) in all cases elevated CO2 signifi cantly (Table 7) Significant interactions of CO

2 with tillage occurred

increased WUE in both tillage treatments with a greater mag- on the final two sampling dates (DOY 224 and 226) (Table 7) nitude of response under NT elevated CO


n only under NT

Elevated CO2 significantly increased seasonal averages for Elevated CO

2 significantly increased seasonal averages for

WUE in each of the 3 yr (Tables 2ndash4 Fig 1ndash3) and when aver- P n in each of the 3 yr (Tables 5ndash7 Fig 4ndash6) and when averaged

aged across all three seasons (P lt 0001) These seasonal and across all three seasons (P lt 0001) No-till signifi cantly reduced total averages reflected no main effect of tillage (total average P = P in 2000 (Table 5) and when averaged across all seasons (P

n

0263) Interactions of CO and tillage occurred in 2001 (Table = 0054) There were no significant interactions between CO2 2

3) in 2003 (Table 4) and when averaged across all three seasons









and tillage on seasonally averaged P n

(total average P = 0785) (Tables 5ndash7)

In 2000 elevated CO2 signifi cantly

reduced gs on 5 of 13 sampling dates

(Table 5 Fig 4b) No-till reduced gs

only on DOY 193 (Table 5) No sigshy

nificant interaction of CO2 and tillage

was observed (Table 5)


cantly reduced gs on seven of nine

sampling dates (Table 6 Fig 5b)

Similar to 2000 NT reduced gs only

on one date (DOY 199) (Table 6)

and no significant interactions of CO2

and tillage were observed (Table 6)


cantly reduced gs on the final 6 of the

10 sampling dates (Table 7 Fig 6b)

No-till signifi cantly reduced gs on only

DOY 217 (Table 7) Signifi cant intershy

actions of CO2 with tillage occurred

on two dates (Table 7) On DOY 212

elevated CO2 reduced g

s only under

CT On DOY 226 elevated CO2

reduced gs in both tillage treatments

with the magnitude of response being

greater in the CT system


seasonal averages for gs in each of the


averaged across all three seasons (P lt 0001) These seasonal and total

averages reflected no main eff ect of

tillage (total average P = 0207) A

significant interaction between CO2

and tillage occurred in 2004 (Table

7) when elevated CO2 reduced the

seasonal average for gs in both tillshy

age treatments with the magnitude

of response being greater in CT Th e


did not aff ect gs when averaged across

the three seasons (P = 0245)


reduced Tr on only 3 of 13 sampling

dates (Table 5 Fig 4c) No-till signifshy

icantly reduced Tr only on DOY 193

(Table 5) A single signifi cant interacshy

tion of CO2 and tillage was noted on

DOY 196 (Table 5) Elevated CO2

reduced Tr under NT unexpectedly

elevated CO2 increased Tr under CT

Elevated CO2 signifi cantly

reduced Tr on 6 of 9 sampling dates

in 2002 (Table 6 Fig 5c) Th ere were

no significant main effects of tillage or

interactions of CO2 with tillage on Tr

(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O

mminus2 sminus1) P n photosynthesis (μmol CO

2 mminus2 sminus1) Till tillage system Tr transpiration (mmol H

2O mminus2 sminus1) WUE water use effi ciency (μmol CO

2 mmolminus1 H

2O)

Table 5 Statistics (Pr gt F italics represent significance) for carbon dioxide concentration tillage system and their interaction on sorghum gas exchange variables for the various sampling dates in 2000


DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O


Th e effect of CO2 on Tr in 2004 was similar to 2002 in Elevated CO

2 significantly reduced seasonal averages for Tr in

that elevated CO2 significantly reduced Tr on 7 of 10 sam- each of the 3 yr (Tables 5ndash7 Fig 4ndash6) and when averaged across

pling dates (Table 7 Fig 6c) Also similar to 2002 there were all three seasons (P lt 0001) These seasonal and total averages

no main effects of tillage on Tr (Table 7) However signifi cant reflected no main effect of tillage (total average P = 0323) or

interactions of CO2 and tillage were noted on two dates (Table interaction between CO

2 and tillage (total average P = 0868)

7) On DOY 212 elevated CO2 reduced Tr only under CT On As with soybean WUE was the most consistent variable

DOY 224 elevated CO2 significantly reduced Tr in both sys- measured in sorghum In 2000 elevated CO

2 signifi cantly

tems with the magnitude of response being greater under CT increased WUE on all but one date (Table 5 Fig 4d) Th ere

were no main effects of tillage on WUE (Table 5) A signifi shy









cant interaction of CO2 with tillage

was observed on DOY 187 (Table

5) elevated CO2 increased WUE in

both systems with the magnitude of

response being slightly greater under

NT conditions


cantly increased WUE on all dates

(Table 6 Fig 5d) As in 2000 there

were no main effects of tillage on

WUE and there was only one signifi shy

cant interaction (DOY 206) (Table 6)

when elevated CO2 increased WUE

in both systems with the magnitude

of response being greater under NT

As in 2002 elevated CO2 signifi shy


in 2004 (Table 7 Fig 6d) No-till

significantly reduced WUE on DOY

210 (Table 7) As in the previous 2

yr a single significant interaction of

CO2 and tillage occurred (Table 7)

on DOY 212 elevated CO2 increased

WUE only under CT


increased seasonal averages for WUE

in each of the 3 yr (Tables 5ndash7 Fig

4ndash6) and when averaged across all

three seasons (P lt 0001) Th ese seashy

sonal and total averages refl ected no

main effect of tillage (total average P = 0913) or interaction between CO

2

and tillage (total average P = 0310)

Discussion Conservation agricultural practices

can be beneficial in terms of reduced

erosion and increased water infi ltrashy

tion and soil C storage leading to

better nutrient and water retention

(Phillips et al 1980 Gebhardt et al

1985 Kern and Johnson 1993 Hunt

et al 1996 Diaz-Zorita et al 2002

Triplett and Dick 2008) Residues left

on the soil surface in NT systems act

as a mulch that enhances water infi lshy

tration reduces evaporation and aids

in water conservation (Unger 1984

Norwood 1994 Reicosky et al

1999) It is expected that these benefi ts

would result in increased crop growth

and yield which has led to widespread

adoption of NT systems in the last two

decades (CTIC 2004) However the

effects of conservation practices on

crop yield have been inconsistent with

increases decreases or no eff ect being

reported (Edwards et al 1988 Torbert


et al 2001 2009 Izumi et al 2004

Balkcom et al 2006) For example

sorghum yields from this study showed

a significant increase (109) in 2000

a nonsignificant increase (45) in

2003 and a nonsignifi cant decrease

(minus32) in 2004 under NT compared

with CT (data not shown) Tillage

treatment had no statistically signifi shy

cant impact on soybean yields in all 3

yr however the yield was 62 higher

under NT in 1999 but was 44 and

55 lower under NT in 2001 and

2003 respectively (data not shown)

Studies that might explain this

variability by examining the eff ects

of conservation practices on crop

physiology (ie photosynthesis and

gas exchange) are lacking Given the

inconsistent yield responses alluded

to above one would expect that gas

exchange measures would also vary

Tennakoon and Hulugalle (2006)

reported no difference in WUE and

Tr between minimum tilled and conshy

ventionally tilled cotton Data from

the current study support this fi ndshy

ing Signifi cant effects of tillage on gas

exchange measures were infrequent

and varied as to whether NT resulted

in an increase or a decrease For examshy

ple tillage signifi cantly aff ected P n on

only five sampling dates across the 3 yr

of study in soybean and on only eight

dates in sorghum P n was lower under

NT on three dates in soybean and on

seven dates in sorghum (Tables 2ndash7)

Other gas exchange measures folshy

lowed a similar pattern These data are

supported by the fact that the eff ects

of tillage on plant biomass (a cumulashy

tive measure of season-long photosynshy

thate production) were also small and

variable (Prior et al 2005)

Available soil water is necessary to

maintain adequate rates of P n during

crop development and water defi cit is

known to decrease P n and Tr (Boyer

1982) Therefore when plant-available

water is adequate NT may have little

effect on crop gas exchange However

given the benefi cial effects of NT on soil

water P n rates can be sustained at least

into early drought stages Arriaga et al

(2009) found that tillage had little eff ect

on cotton gas exchange measurements

when rainfall was frequent Under

drought conditions NT plots conshy

served soil water and maintained higher

Fig 4 Sorghum gas exchange measures taken during reproductive growth in 2000 (a) Photosynthesis (P


s) (c) Transpiration (Tr) and (d) Water use effi ciency (WUE) Sorghum




are seasonal averages averages followed by different letters were signifi cantly diff erent (LSMeans procedure Proc Mixed SAS P le 010 n = 3) Growth stages are noted at the top of the figure S6 (half bloom) S7 (soft dough) and S8 (hard dough)




DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O


rates of P n however even this result was sporadically observed whether a CO

2 response was observed in NT CT or both (with

The ability of NT to maintain P n rates depends on the duration a difference in magnitude or direction) This was somewhat

of drought eventually soil water is depleted and P n subsequently unexpected given the increased residue inputs and concomitant

declines In addition to effects on soil water NT can aff ect plant rise in soil C seen under elevated CO2 and in the NT system

rooting Due to the potential for higher mechanical impedance (Prior et al 2005) However given the rarity and variability in

in NT soils root penetration can be restricted to shallower soil tillage effects on gas exchange variables perhaps this should not

depths (Izumi et al 2004 Iijima et al 2007) Furthermore the have been surprising It is possible that some of these infrequent

mulching effect of additional unincorporated residues (including interactions were merely due to biotic or instrumental noise

cover crop and nonyield residue from the previous row crop) in In contrast to the paucity of data on the effects of tillage on crop

conservation systems (Prior et al 2005) may also favor a shal- gas exchange the impact of elevated CO2 on these measures has

lower root system This was observed with sorghum in our system been intensively examined The best documented and repeatable

where NT favored shallow root systems whereas CT favored response to atmospheric CO2 enrichment is a signifi cant increase

deeper rooting (Pritchard et al 2006) Having more roots in the in photosynthesis of C3 plants (Rogers et al 1983b Long and

upper soil profile may lead to more rapid depletion of soil water in Drake 1992 Woodward 1992 Amthor 1995) This increased C

this zone during drought It is possible that rainfall was frequent uptake and assimilation generally results in increased crop growth

enough in the present study to dampen the benefi cial eff ects of under CO2ndashenriched conditions For C

3 plants positive responses

NT on soil water conservation resulting in little effect on crop gas to elevated CO2 are mainly attributed to competitive inhibition

exchange The fact that CT tended to have higher P n rates (on the of photo-respiration by CO

2 and the internal CO

2 concentrations

few dates when a signifi cant effect of tillage was observed) may be of C3 leaves (at current CO

2 levels) being less than the Michaelisshy

a result of deeper rooting in this system Menton constant of ribulose bisphosphate carboxylaseoxygenase

As with the effects of tillage systems interactions between till- (Amthor and Loomis 1996) However the CO2ndashconcentrating

age and CO2 were rarely observed (Tables 2ndash7) and varied as to mechanism used by C

4 species limits the response to CO

2 enrich-









ment (Amthor and Loomis 1996)

Th ese differences in CO2 utilization

during photosynthesis result in the fact

that plants with a C3 photosynthetic

pathway often exhibit greater growth

response relative to those with a C4

pathway (Bowes 1993 Poorter 1993

Amthor 1995 Amthor and Loomis

1996 Rogers et al 1997) Summaries

have consistently shown that biomass

response to atmospheric CO2 enrichshy

ment varies between plants with a C3

(33ndash40 increase) vs a C4 (10ndash15

increase) photosynthetic pathway

(Kimball 1983 Prior et al 2003)

Data from the current study supshy

port this response pattern Across the

entire study elevated CO2 signifi cantly

increased soybean (a C3 crop) P

n by

485 In comparison sorghum (a C4

crop) P n was also signifi cantly increased

by elevated CO2 but only by 155

these numbers are analogous to those

mentioned above Across the entire

study elevated CO2 increased soybean

P n on 83 of sampling dates (Tables

2ndash4 Fig 1ndash3) Soybean P n began to

taper off toward the end of each season

due to crop senescence and days when

soybean showed no signifi cant CO2

response tended to occur during these

later periods Significant increases in

sorghum P n tended to occur sporadishy

cally across the growing seasons (Tables

5ndash7 Fig 4ndash6) and were observed less

frequently (on 53 of sampling dates)

than in soybean The late-season tapershy

ing effect observed in soybean was not

seen in the sorghum crops Th is was

logical in that sorghum is harvested at

physiological maturity when plants are

still green whereas soybeans are harshy

vested after plants defoliate and dry

In addition to eff ects on P n eleshy

vated CO2 is known to decrease g

s and

Tr (Eamus and Jarvis 1989 Rogers et

al 1983b Prior et al 1991) Th ese

reductions in gs and Tr are due to the

fact that elevated CO2 induces the

partial closure of stomates on leaf surshy

faces this is true for C3 and C

4 crops

(Rogers and Dahlman 1993 Allen

and Amthor 1995) In general CO2ndash

induced growth stimulation in C3

plants is primarily caused by increased

P n whereas in C

4 plants it is mainly

caused by reduced gs and Tr

In the present study gs and Tr genshy

erally decreased in both crops exposed









to elevated CO2 In soybean these

responses were less consistent than

CO2 eff ects on P

n and signifi cant

effects of elevated CO2 occurred on

only 47 and 37 of sampling dates for

gs and Tr respectively (Tables 2ndash4 Fig

1ndash3) Elevated CO2 reduced soybean

gs (333) and Tr (170) compared

with the 485 increase seen in P In n

sorghum signifi cant effects of CO2 on

gs and Tr tended to occur sporadically

across the growing seasons signifi cant

reductions occurred on 53 and 59

of sampling dates (Tables 5ndash7 Fig

4ndash6) These numbers are similar to the

increases observed in P n Elevated CO

2

decreased sorghum gs and Tr by 297

and 207 across all years which was

larger than the 155 increase in P n

Water use efficiency is a measure of

the amount of carbon fixed per unit of

water used It is calculated by dividing

P n by Tr and therefore is influenced by a

combination of these factors Elevated

atmospheric CO2 generally results in

increased WUE for plants with C3 and

C4 photosynthetic pathways (Rogers et

al 1983b Amthor 1995) Data from

the current study are no exception to

this rule In fact increased WUE under

elevated CO2 was the most consistent

response noted for both species with

soybean (Tables 2ndash4 Fig 1ndash3) showshy

ing ~70 greater increase in WUE

than sorghum (Tables 5ndash7 Fig 4ndash6)

In C3 plants P

n generally plays a more

important role in determining WUE

whereas in C4 plants Tr is usually the

more dominant factor (Rogers and

Dahlman 1993) Soybean in our study

was consistent with this pattern in that

it showed a greater P n than Tr response

to elevated CO2 (Tables 2ndash4) the

response of Tr was slightly greater than

P n in sorghum (Tables 5ndash7)

In summary tillage had infreshy

quent and inconsistent eff ects on

gas exchange in soybean and grain

sorghum through a 6-yr fi eld study

Increased photosynthesis decreased

stomatal conductance and transhy

spiration (leading to dramatically

increased WUE) were consistently

seen in both species when grown

under elevated CO2 these eff ects

tended to be greater in soybean than

in sorghum Biomass production in

this cropping system study followed

similar response patterns to tillage


and CO2 (Prior et al 2005) These results suggest that high

rates of photosynthesis can occur in CO2ndashenriched environshy

ments during reproductive growth in both tillage systems

When this increased photosynthesis is combined with more

efficient use of water greater productivity results from the

rising concentration of atmospheric CO2

Acknowledgments The authors thank BG Dorman and JW Carrington for technical

assistance This research was supported by the Biological and

Environmental Research Program (BER) US Department of Energy

Interagency Agreement No DE-AI02-95ER62088

References Adams JF CC Mitchell and HH Bryant 1994 Soil test recommendashy

tions for Alabama crops Agronomy and Soils Departmental Series 178 Alabama Agric Exp Stn Auburn

Allen LH Jr and JS Amthor 1995 Plant physiological responses to elshyevated CO

2 temperature air pollution and UV-B radiation p 51ndash84

In GM Woodwell and FT Mackenzie (ed) Biotic feedbacks in the global climatic system Will the warming feed the warming Oxford Univ Press New York

Amthor JS 1995 Terrestrial higher-plant response to increasing atmosphershyic [CO

2] in relation to the global carbon cycle Global Change Biol

1243ndash274

Amthor JS and RS Loomis 1996 Integrating knowledge of crop responses to elevated CO

2 and temperature with mechanistic simulation models

Model components and research needs p 317ndash346 In GW Koch and HA Mooney (ed) Carbon dioxide and terrestrial ecosystems Academic Press San Diego CA

Arriaga FJ SA Prior JF Terra and DP Delaney 2009 Conventional tillshyage and no-tillage effects on cotton gas exchange in standard and ultra-narrow row systems Commun Biometry Crop Sci 442ndash51

Balkcom KS DW Reeves JN Shaw CH Burmester and LM Curtis 2006 Cotton yield and fiber quality from irrigated tillage systems in the Tennessee Valley Agron J 98596ndash602

Batchelor JA Jr 1984 Properties of bin soils at the National Tillage Mashychinery Laboratory Publ 218 USDAndashARS National Soil Dynamics Laboratory Auburn AL

Bowes G 1993 Facing the inevitable Plants and increasing atmospheric CO

2 Annu Rev Plant Physiol Plant Mol Biol 44309ndash332

Boyer JS 1982 Plant productivity and environment Science 218443ndash448

Carreker JR SR Wilkinson AP Barnett and JE Box 1977 Soil and washyter management systems for sloping land ARS-S-160 USDA Washshyington DC

CTIC 2004 National crop residue management survey Available at http wwwconservationinformationorg (verified 22 Jan 2010) Conservation Technology Information Center West Lafayette IN

Diaz-Zorita M GA Duarte and JH Grove 2002 A review of no-till sysshytems and soil management for sustainable crop production in the sub-humid and semiarid Pampas of Argentina Soil Tillage Res 651ndash18

Eamus D and PG Jarvis 1989 The direct effects of increase in the global atmospheric CO

2 concentration on natural and commercial temperate

trees and forests Adv Ecol Res 191ndash55

Edwards JH DL Thurlow and JT Eason 1988 Influence of tillage and crop rotation on yields of corn soybean and wheat Agron J 8076ndash80

Gebhardt MR TC Daniel EE Schweizer and RA Allmaras 1985 Conshyservation tillage Science 230625ndash630

Hunt PG DL Karlen TA Matheny and VL Quisenberry 1996 Changes in carbon content of a Norfolk loamy sand after 14 years of conservation and conventional tillage J Soil Water Conserv 51255ndash258

Iijima M S Morita W Zegada-Lizarazu and Y Izumi 2007 No-tillage enshyhanced the dependance on surface irrigation water in wheat and soybean Plant Prod Sci 10182ndash188

Izumi Y K Uchida and M Iijima 2004 Crop production in successive wheat-soybean rotation with no-tillage practice in relation to the root system development Plant Prod Sci 7329ndash336

Keeling CD and TP Whorf 2001 Atmospheric CO2 records from sites in

the SIO air sampling network p 14ndash21 In Trends A compendium of data on global change Carbon Dioxide Information Analysis Center Oak Ridge National Laboratory USDOE Oak Ridge TN

Kern JS and MG Johnson 1993 Conservation tillage impacts on national

608

soil and atmospheric carbon levels Soil Sci Soc Am J 57200ndash210

Kimball BA 1983 Carbon dioxide and agricultural yield An assemblage and analysis of 770 prior observations Rep 14 USDAndashARS Water Consershyvation Laboratory Phoenix AZ

Kimball BA K Kobayashi and M Bindi 2002 Responses of agricultural crops to free-air CO

2 enrichment Adv Agron 77293ndash368

Littell RC GA Milliken WW Stroup and RD Wolfinger 1996 SAS system for mixed models SAS Inst Cary NC

Long SP and BG Drake 1992 Photosynthetic CO2 assimilation and risshy

ing atmospheric CO2 concentrations p 69ndash107 In NR Baker and H

Thomas (ed) Crop photosynthesis Spatial and temporal determinants Elsevier New York

Norwood CA 1994 Profi le water distribution and grain yield as aff ected by cropping system and tillage Agron J 86558ndash563

Phillips RE RL Blevins GW Thomas WW Frye and SH Phillips 1980 No-tillage agriculture Science 2081108ndash1113

Poorter H 1993 Interspecific variation in the growth response of plants to an elevated ambient CO

2 concentration Vegetatio 10410577ndash97

Prior SA HH Rogers N Sionit and RP Patterson 1991 Effects of elshyevated atmospheric CO

2 on water relations of soya bean Agric Ecosyst

Environ 3513ndash25

Prior SA GB Runion HA Torbert HH Rogers and DW Reeves 2005 Elevated atmospheric CO

2 effects on biomass production and soil carbon

in conventional and conservation cropping systems Global Change Biol 11657ndash665

Prior SA HA Torbert GB Runion and HH Rogers 2003 Implications of elevated CO

2ndashinduced changes in agroecosystem productivity J Crop

Prod 8217ndash244

Pritchard SG SA Prior HH Rogers MA Davis GB Runion and TW Popham 2006 Effects of elevated atmospheric CO

2 on root dynamshy

ics and productivity of sorghum grown under conventional and conshyservation agricultural management practices Agric Ecosyst Environ 113175ndash183

Reicosky DC DW Reeves SA Prior GB Runion HH Rogers and RL Raper 1999 Effects of residue management and controlled traffi c on carbon dioxide and water loss Soil Tillage Res 52153ndash165

Ritchie SW JJ Hanway HE Thompson and GO Benson 1992 How a soyshybean plant develops Spec Rep 53 Iowa State Univ Coop Ext Serv Ames

Rogers HH and RC Dahlman 1993 Crop responses to CO2 enrichment

Vegetatio 104105117ndash131

Rogers HH WW Heck and AS Heagle 1983a A field technique for the study of plant responses to elevated carbon dioxide concentrations Air Pollut Control Assoc J 3342ndash44

Rogers HH GB Runion SV Krupa and SA Prior 1997 Plant responses to atmospheric CO

2 enrichment Implications in root-soil-microbe interacshy

tions p 1ndash34 In LH Allen Jr et al (ed) Advances in carbon dioxide efshyfects research ASA Spec Publ 61 ASA CSSA and SSSA Madison WI

Rogers HH GB Runion SA Prior and HA Torbert 1999 Response of plants to elevated atmospheric CO

2 Root growth mineral nutrition

and soil carbon p 215ndash244 In Y Luo and HA Mooney (ed) Carbon dioxide and environmental stress Academic Press San Diego CA

Rogers HH JF Thomas and GE Bingham 1983b Response of agroshynomic and forest species to elevated atmospheric carbon dioxide Science 220428ndash429

Tennakoon SB and NR Hulugalle 2006 Impact of crop rotation and minimum tillage on water use efficiency of irrigated cotton in a Vertisol Irrig Sci 2545ndash52

Torbert HA E Krueger D Kurtener and KN Potter 2009 Evaluation of tillage systems for grain sorghum and wheat yields and total nitrogen uptake in the Texas Blackland Prairie J Sustainable Agric 3396ndash106

Torbert HA KN Potter and JE Morrison Jr 2001 Tillage system fertilshyizer nitrogen rate and timing effect on corn yields in the Texas Blackland Prairie Agron J 931119ndash1124

Torbert HA SA Prior HH Rogers and CW Wood 2000 Review of elevated atmospheric CO

2 effects on agro-ecosystems Residue decomposhy

sition processes and soil carbon storage Plant Soil 22459ndash73

Triplett GB Jr and WA Dick 2008 No-tillage crop production A revolushytion in agriculture Agron J 100S153ndashS165

Unger PW 1984 Tillage and residue effects on wheat sorghum and sunshyflower grown in rotation Soil Sci Soc Am J 48885ndash891

Vanderlip RL 1979 How a sorghum plant develops Kansas State Univ Coop Ext Serv Manhattan

Woodward FI 1992 Predicting plant responses to global environmental change New Phytol 122239ndash251

Journal of Environmental Quality bull Volume 39 bull MarchndashApril 2010

in response could become important with regard to future manshy

agement decisions There have been no long-term studies comshy

paring conventional tillage (CT) with conservation tillage or

no-tillage (NT) systems under varying levels of atmospheric CO2

The objective of the current study was to examine the interactive

effects of management (CT and NT) and atmospheric CO2 conshy

centration (ambient and twice ambient) on leaf-level gas exchange

during row crop (soybean a N-fi xing C3 crop and grain sorghum

a C4 crop) reproductive growth over multiple seasons

Materials and Methods This study was conducted on an outdoor soil bin (7 m by 76

m) at the USDAndashARS National Soil Dynamics Laboratory in

Auburn Alabama (326deg N 855deg W) The bin was fi lled with

a Decatur silt loam soil (clayey kaolinitic thermic Rhodic

Paleudults) (Batchelor 1984) Open-top chambers comprised

of a structural aluminum frame (3 m in diameter by 24 m in

height) covered with a 02-mm PVC film panel (Rogers et al

1983a) were used for CO2 exposure Carbon dioxide was supshy

plied from a 127-Mg liquid CO2 receiver through a high-volume

dispensing manifold and the atmospheric CO2 concentration

was elevated by continuous injection of CO2 into plenum boxes

Air was introduced into each chamber through the bottom half

of each chamber cover which was double-walled the inside wall

was perforated with 25-cm-diameter holes to serve as ducts to

distribute air uniformly into the chamber Three chamber volshy

umes were exchanged every minute Carbon dioxide concentrashy

tions were continually monitored (24 h dminus1) using a time-shared

manifold with samples drawn through solenoids to an infrared

CO2 analyzer (Model 6252 LI-COR Inc Lincoln NE) Th e

target concentration for the elevated CO2 treatment was twice

ambient (~720 μL Lminus1) The mean (plusmn SE) daytime CO2 concenshy

trations across the six growing seasons of the study were 36635

plusmn 007 and 69180 plusmn 031 for the ambient and elevated CO2

treatments respectively (n = 58230) Plot locations were permashy

nently delineated using an anchored structural aluminum ring

(3 m in diameter) as a precaution to prevent lateral surface fl ow

of water into or out of plots

Two crop management systems (CT and NT) were estabshy

lished in the fall of 1997 In the CT system grain sorghum

[Sorghum bicolor (L) Moench lsquoPioneer 8282rsquo] and soybean

[Glycine max (L) Merr lsquoAsgrow 6101rsquo] were rotated each year

with spring tillage after winter fallow The NT system also used

a grain sorghum and soybean rotation with three cover crops

[crimson clover (Trifolium incarnatum L lsquoAU Robinrsquo) sunn

hemp (Crotalaria juncea L lsquoTropic Sunnrsquo) and wheat (Triticum aestivum L lsquoPioneer 2684rsquo)] grown using no-tillage practices In

both management systems row crop seeds were sown (20 per

meter of row) on 038-m row spacings Planting dates for soyshy

bean were 19 23 and 27 May for 1999 2001 and 2003 respecshy

tively dates for sorghum were 2 6 and 12 May for 2000 2002

and 2004 respectively Extension recommendations were used

in managing the crops fertilizer rates were based on standard soil

tests guidelines as recommended by the Auburn University Soil

Testing Laboratory (Adams et al 1994) Soybeans were grown

with no nitrogen fertilization but seeds were inoculated with

commercial Rhizobium (Nitragin Co Milwaukee WI) before

planting For grain sorghum fertilizer N (ammonium nitrate)

was hand-broadcast at a rate of 34 kg N haminus1 shortly after plantshy

ing and an additional 101 kg N haminus1 was similarly applied 30

d after planting Cover crops and sorghum (regrowth prevenshy

tion) were terminated with glyphosate (N-[phosphonomethyl]

glycine) 10 d before planting the following crop All crops were

harvested using standard procedures yield and biomass were

recorded as described in detail by Prior et al (2005) Harvest

dates for soybean were 25 22 and 20 October for 1999 2001

and 2003 respectively dates for sorghum were 14 14 and 17

August for 2000 2002 and 2004 respectively After harvest all

remaining residues were uniformly spread over their respective

study plot All operations described above were also conducted

on nonexperimental areas to ensure uniform treatment of areas

bordering the study plots

During reproductive growth for 6 yr leaf level measureshy

ments of photosynthesis (P n) stomatal conductance (g

s) and

transpiration (Tr) were made twice weekly using a LI-6400

Portable Photosynthesis System (LI-COR Inc Lincoln NE)

for soybean (C3 photosynthesis) and grain sorghum (C

4 phoshy

tosynthesis) Visual assessments of approximate growth stage

were also conducted during this period for soybean (Ritchie

et al 1992) and sorghum (Vanderlip 1979) Gas exchange

measurements were taken at midday on leaves (fully expanded

sun-exposed leaves at the canopy top) from three randomly

selected plants per plot and were initiated at the start of reproshy

ductive growth Water use effi ciency (μmol CO2 mmolminus1 H

2O)

was calculated by dividing P n by Tr (ie μmol CO

2 mminus2 sminus1

mmol H2O mminus2 sminus1) Rainfall was recorded on site throughout

each sampling period (Table 1)

The experiment was conducted using a split-plot design with

three replicate blocks Whole-plot treatments (tillage system)

were randomly assigned to half of each block Split-plot treatshy

ments (CO2 levels) were randomly assigned to two chambers

(3 m in diameter) within each whole plot There were a total of

12 chamber plot locations six were ambient CO2 treatments

(three for CT and three for NT) and six were elevated CO2

treatments (three for CT and three for NT) Data from each

chamber were averaged before statistical analysis Statistical

analyses of data were performed using the Mixed procedure of

the Statistical Analysis System (Littell et al 1996) A signifi shy

cance level of P le 010 was established a priori

Results

Soybean In 1999 elevated CO


n on 17 of 21

sampling dates (Table 2 Fig 1a) Days without a signifi cant

CO2 effect tended to occur later in the growing season when

Table 1 Rainfall recorded on site during each sampling period (the growshying season and sampling period for soybean is longer than for sorghum)

Species Year Rainfall No of events No gt10 mm

mm

Soybean 1999 16129 14 5

2001 15621 15 5

2003 26162 18 9

Sorghum 2000 8890 9 3

2002 6731 7 3

2004 18415 9 5




DOYdagger P n

gs

Tr WUE


196 0007 0578 0482 0507 0688 0611 0331 0910 0486 lt0001 0372 0711

200 0002 0720 0602 0007 0805 0239 0015 0584 0171 lt0001 0761 0004

202 lt0001 0692 0258 0007 0777 0394 0021 0364 0868 lt0001 0440 0874

207 0006 0880 0494 0356 0441 0990 0270 0612 0951 0007 0514 0976

210 0006 0168 0606 0633 0192 0820 0861 0170 0974 0003 0511 0287

214 0003 0158 0310 0430 0202 0386 0426 0192 0157 0005 0142 0052

218 0001 0353 0013 0781 0120 0058 0958 0372 0080 lt0001 0434 0107

221 0009 0165 0724 0339 0246 0418 0515 0227 0748 0002 0613 0825

224 0022 0257 0739 0813 0560 0600 0477 0763 0662 0004 0126 0223

228 0012 0220 0641 0545 0326 0522 0844 0398 0518 lt0001 0737 0958

231 0163 0242 0506 0420 0950 0498 0604 0607 0728 0013 0258 0185

238 lt0001 0309 0025 0098 0455 0241 0284 0110 0172 0001 0748 0935

242 lt0001 0156 0102 0005 0117 0017 0036 0312 0055 0001 0785 0956

246 0005 0367 0625 0085 0657 0610 0055 0653 0517 lt0001 0633 0384

250 0015 0766 0718 0109 0650 0610 0130 0297 0643 0003 0112 0682

253 0122 0876 0730 0050 0618 0737 0013 0977 0706 lt0001 0794 0976

257 0018 0324 0008 0010 0634 0021 0008 0899 0012 0003 0702 0883

260 0051 0283 0728 0213 0466 0948 0257 0280 0926 0004 0710 0929

264 0406 0837 0206 0021 0119 0126 0016 0306 0099 0003 0530 0545

267 0023 0854 0660 0412 0699 0536 0448 0706 0683 lt0001 0081 0555

273 0573 0979 0696 0006 0442 0712 0008 0577 0802 lt0001 0184 0422

Avg lt0001 0324 0620 0002 0649 0474 0005 0861 0400 lt0001 0125 0148



2O




2



n under NT



n under CT








2




n under NT


n on 17 of 19







2



n under




n






2 treatshy


















2 and




s in the NT



s under CT


s on 10 of





s (Table 4)


s in













average P = 0821)


























the NT treatment






















average P = 0611)











DOYdagger P n

gs

Tr WUE


198 0092 0222 0765 0231 0091 0884 0169 0066 0784 lt0001 0119 0335

200 0008 0386 0397 0383 0355 0412 0348 0429 0145 0002 0567 0334

205 lt0001 0920 0867 0001 0595 0654 0002 0993 0787 0005 0993 0918

208 lt0001 0248 0105 0089 0674 0682 0280 0480 0632 lt0001 0060 0284

212 lt0001 0605 0944 0312 0678 0890 0551 0702 0941 lt0001 0813 0541

215 0130 0757 0129 0107 0944 0042 0022 0680 0029 0008 0325 0353

220 0003 0146 0320 0012 0012 0007 0139 0061 0051 0006 0738 0256

222 0094 0533 0724 0024 0353 0386 0018 0326 0402 lt0001 0256 0563

226 lt0001 0231 0002 lt0001 0003 0630 0001 0195 0421 lt0001 0535 0233

229 0008 0664 0929 0002 0390 0468 0024 0818 0567 lt0001 0727 0288

233 0006 0985 0365 0615 0853 0445 0871 0844 0526 0009 0520 0386

236 0002 0349 0009 0916 0718 0186 0711 0597 0206 0001 0830 0088

240 0177 0249 0103 lt0001 0902 0127 lt0001 0484 0255 lt0001 0636 0652

243 0041 0943 0636 0607 0644 0044 0575 0601 0114 0003 0092 0035

247 0018 0468 0270 0001 0529 0236 0003 0366 0237 lt0001 0338 0466

249 0012 0944 0111 0538 0324 0161 0748 0529 0196 0001 0505 0940

255 0015 0583 0627 0035 0598 0712 0023 0385 0924 lt0001 0746 0987

257 0013 0412 0519 0757 0240 0761 0752 0454 0458 0001 0423 0707

262 0835 0048 0859 0080 0116 0675 0078 0105 0957 0002 0540 0124

264 0031 0640 0451 0683 0669 0469 0798 0626 0481 lt0001 0611 0218

268 0254 0945 0458 0192 0750 0449 0217 0813 0525 0002 0931 0654

270 0638 0601 0136 0682 0419 0234 0703 0348 0258 lt0001 0157 0006

Avg lt0001 0849 0797 lt0001 0613 0987 0002 0959 0981 lt0001 0555 0081



2O









n on 6 of 13




2






2 with


2











n only under NT





n


































s only under


































(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy



























DOYdagger P n

gs

Tr WUE


196 0007 0578 0482 0507 0688 0611 0331 0910 0486 lt0001 0372 0711

200 0002 0720 0602 0007 0805 0239 0015 0584 0171 lt0001 0761 0004

202 lt0001 0692 0258 0007 0777 0394 0021 0364 0868 lt0001 0440 0874

207 0006 0880 0494 0356 0441 0990 0270 0612 0951 0007 0514 0976

210 0006 0168 0606 0633 0192 0820 0861 0170 0974 0003 0511 0287

214 0003 0158 0310 0430 0202 0386 0426 0192 0157 0005 0142 0052

218 0001 0353 0013 0781 0120 0058 0958 0372 0080 lt0001 0434 0107

221 0009 0165 0724 0339 0246 0418 0515 0227 0748 0002 0613 0825

224 0022 0257 0739 0813 0560 0600 0477 0763 0662 0004 0126 0223

228 0012 0220 0641 0545 0326 0522 0844 0398 0518 lt0001 0737 0958

231 0163 0242 0506 0420 0950 0498 0604 0607 0728 0013 0258 0185

238 lt0001 0309 0025 0098 0455 0241 0284 0110 0172 0001 0748 0935

242 lt0001 0156 0102 0005 0117 0017 0036 0312 0055 0001 0785 0956

246 0005 0367 0625 0085 0657 0610 0055 0653 0517 lt0001 0633 0384

250 0015 0766 0718 0109 0650 0610 0130 0297 0643 0003 0112 0682

253 0122 0876 0730 0050 0618 0737 0013 0977 0706 lt0001 0794 0976

257 0018 0324 0008 0010 0634 0021 0008 0899 0012 0003 0702 0883

260 0051 0283 0728 0213 0466 0948 0257 0280 0926 0004 0710 0929

264 0406 0837 0206 0021 0119 0126 0016 0306 0099 0003 0530 0545

267 0023 0854 0660 0412 0699 0536 0448 0706 0683 lt0001 0081 0555

273 0573 0979 0696 0006 0442 0712 0008 0577 0802 lt0001 0184 0422

Avg lt0001 0324 0620 0002 0649 0474 0005 0861 0400 lt0001 0125 0148



2O




2



n under NT



n under CT








2




n under NT


n on 17 of 19







2



n under




n






2 treatshy


















2 and




s in the NT



s under CT


s on 10 of





s (Table 4)


s in













average P = 0821)


























the NT treatment






















average P = 0611)











DOYdagger P n

gs

Tr WUE


198 0092 0222 0765 0231 0091 0884 0169 0066 0784 lt0001 0119 0335

200 0008 0386 0397 0383 0355 0412 0348 0429 0145 0002 0567 0334

205 lt0001 0920 0867 0001 0595 0654 0002 0993 0787 0005 0993 0918

208 lt0001 0248 0105 0089 0674 0682 0280 0480 0632 lt0001 0060 0284

212 lt0001 0605 0944 0312 0678 0890 0551 0702 0941 lt0001 0813 0541

215 0130 0757 0129 0107 0944 0042 0022 0680 0029 0008 0325 0353

220 0003 0146 0320 0012 0012 0007 0139 0061 0051 0006 0738 0256

222 0094 0533 0724 0024 0353 0386 0018 0326 0402 lt0001 0256 0563

226 lt0001 0231 0002 lt0001 0003 0630 0001 0195 0421 lt0001 0535 0233

229 0008 0664 0929 0002 0390 0468 0024 0818 0567 lt0001 0727 0288

233 0006 0985 0365 0615 0853 0445 0871 0844 0526 0009 0520 0386

236 0002 0349 0009 0916 0718 0186 0711 0597 0206 0001 0830 0088

240 0177 0249 0103 lt0001 0902 0127 lt0001 0484 0255 lt0001 0636 0652

243 0041 0943 0636 0607 0644 0044 0575 0601 0114 0003 0092 0035

247 0018 0468 0270 0001 0529 0236 0003 0366 0237 lt0001 0338 0466

249 0012 0944 0111 0538 0324 0161 0748 0529 0196 0001 0505 0940

255 0015 0583 0627 0035 0598 0712 0023 0385 0924 lt0001 0746 0987

257 0013 0412 0519 0757 0240 0761 0752 0454 0458 0001 0423 0707

262 0835 0048 0859 0080 0116 0675 0078 0105 0957 0002 0540 0124

264 0031 0640 0451 0683 0669 0469 0798 0626 0481 lt0001 0611 0218

268 0254 0945 0458 0192 0750 0449 0217 0813 0525 0002 0931 0654

270 0638 0601 0136 0682 0419 0234 0703 0348 0258 lt0001 0157 0006

Avg lt0001 0849 0797 lt0001 0613 0987 0002 0959 0981 lt0001 0555 0081



2O









n on 6 of 13




2






2 with


2











n only under NT





n


































s only under


































(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy



































average P = 0821)


























the NT treatment






















average P = 0611)











DOYdagger P n

gs

Tr WUE


198 0092 0222 0765 0231 0091 0884 0169 0066 0784 lt0001 0119 0335

200 0008 0386 0397 0383 0355 0412 0348 0429 0145 0002 0567 0334

205 lt0001 0920 0867 0001 0595 0654 0002 0993 0787 0005 0993 0918

208 lt0001 0248 0105 0089 0674 0682 0280 0480 0632 lt0001 0060 0284

212 lt0001 0605 0944 0312 0678 0890 0551 0702 0941 lt0001 0813 0541

215 0130 0757 0129 0107 0944 0042 0022 0680 0029 0008 0325 0353

220 0003 0146 0320 0012 0012 0007 0139 0061 0051 0006 0738 0256

222 0094 0533 0724 0024 0353 0386 0018 0326 0402 lt0001 0256 0563

226 lt0001 0231 0002 lt0001 0003 0630 0001 0195 0421 lt0001 0535 0233

229 0008 0664 0929 0002 0390 0468 0024 0818 0567 lt0001 0727 0288

233 0006 0985 0365 0615 0853 0445 0871 0844 0526 0009 0520 0386

236 0002 0349 0009 0916 0718 0186 0711 0597 0206 0001 0830 0088

240 0177 0249 0103 lt0001 0902 0127 lt0001 0484 0255 lt0001 0636 0652

243 0041 0943 0636 0607 0644 0044 0575 0601 0114 0003 0092 0035

247 0018 0468 0270 0001 0529 0236 0003 0366 0237 lt0001 0338 0466

249 0012 0944 0111 0538 0324 0161 0748 0529 0196 0001 0505 0940

255 0015 0583 0627 0035 0598 0712 0023 0385 0924 lt0001 0746 0987

257 0013 0412 0519 0757 0240 0761 0752 0454 0458 0001 0423 0707

262 0835 0048 0859 0080 0116 0675 0078 0105 0957 0002 0540 0124

264 0031 0640 0451 0683 0669 0469 0798 0626 0481 lt0001 0611 0218

268 0254 0945 0458 0192 0750 0449 0217 0813 0525 0002 0931 0654

270 0638 0601 0136 0682 0419 0234 0703 0348 0258 lt0001 0157 0006

Avg lt0001 0849 0797 lt0001 0613 0987 0002 0959 0981 lt0001 0555 0081



2O









n on 6 of 13




2






2 with


2











n only under NT





n


































s only under


































(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy



























DOYdagger P n

gs

Tr WUE


198 0092 0222 0765 0231 0091 0884 0169 0066 0784 lt0001 0119 0335

200 0008 0386 0397 0383 0355 0412 0348 0429 0145 0002 0567 0334

205 lt0001 0920 0867 0001 0595 0654 0002 0993 0787 0005 0993 0918

208 lt0001 0248 0105 0089 0674 0682 0280 0480 0632 lt0001 0060 0284

212 lt0001 0605 0944 0312 0678 0890 0551 0702 0941 lt0001 0813 0541

215 0130 0757 0129 0107 0944 0042 0022 0680 0029 0008 0325 0353

220 0003 0146 0320 0012 0012 0007 0139 0061 0051 0006 0738 0256

222 0094 0533 0724 0024 0353 0386 0018 0326 0402 lt0001 0256 0563

226 lt0001 0231 0002 lt0001 0003 0630 0001 0195 0421 lt0001 0535 0233

229 0008 0664 0929 0002 0390 0468 0024 0818 0567 lt0001 0727 0288

233 0006 0985 0365 0615 0853 0445 0871 0844 0526 0009 0520 0386

236 0002 0349 0009 0916 0718 0186 0711 0597 0206 0001 0830 0088

240 0177 0249 0103 lt0001 0902 0127 lt0001 0484 0255 lt0001 0636 0652

243 0041 0943 0636 0607 0644 0044 0575 0601 0114 0003 0092 0035

247 0018 0468 0270 0001 0529 0236 0003 0366 0237 lt0001 0338 0466

249 0012 0944 0111 0538 0324 0161 0748 0529 0196 0001 0505 0940

255 0015 0583 0627 0035 0598 0712 0023 0385 0924 lt0001 0746 0987

257 0013 0412 0519 0757 0240 0761 0752 0454 0458 0001 0423 0707

262 0835 0048 0859 0080 0116 0675 0078 0105 0957 0002 0540 0124

264 0031 0640 0451 0683 0669 0469 0798 0626 0481 lt0001 0611 0218

268 0254 0945 0458 0192 0750 0449 0217 0813 0525 0002 0931 0654

270 0638 0601 0136 0682 0419 0234 0703 0348 0258 lt0001 0157 0006

Avg lt0001 0849 0797 lt0001 0613 0987 0002 0959 0981 lt0001 0555 0081



2O









n on 6 of 13




2






2 with


2











n only under NT





n


































s only under


































(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy























































s only under


































(Table 6)




DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy



























DOYdagger P n

gs

Tr WUE

CO2

Till C times T CO2

Till C times T CO2

Till C times T CO2

Till C times T

206 lt0001 0873 0784 0533 0388 0791 0410 0258 0453 0005 0235 0287

210 0004 0782 0434 0194 0714 0365 0194 0577 0227 0056 0347 0157

213 lt0001 0663 0069 0157 0641 0105 0411 0711 0198 lt0001 0811 0680

216 0001 0764 0325 0004 0920 0626 0072 0875 0431 lt0001 0838 0695

220 lt0001 0028 0607 0006 0521 0258 0022 0447 0350 0002 0614 0879

225 lt0001 0227 0984 0002 0205 0198 0036 0131 0425 lt0001 0186 0068

227 0007 0638 0251 0081 0454 0323 0222 0692 0415 0010 0824 0818

232 lt0001 0183 0400 0047 0534 0913 0182 0677 0419 lt0001 0576 0014

234 lt0001 0068 0955 0024 0565 0937 0004 0013 0335 lt0001 0853 0530

238 0001 0539 0546 0015 0782 0294 0064 0517 0945 0001 0781 0453

241 lt0001 0025 0154 0021 0010 0140 0215 0024 0966 0001 0223 0151

245 0006 0354 0892 0218 0515 0991 0487 0619 0717 0002 0825 0602

248 0039 0738 0325 0151 0727 0694 0122 0675 0647 lt0001 0489 0673

252 0045 0971 0578 0039 0860 0252 0101 0988 0417 lt0001 0561 0493

255 0001 0016 0087 0305 0013 0150 0171 0040 0099 0001 0944 0130

259 0037 0158 0581 0316 0105 0846 0519 0114 0423 lt0001 0098 0002

262 0347 0439 0834 0215 0302 0568 0215 0276 0921 0013 0542 0138

267 0125 0883 0525 0024 0884 0857 0006 0784 0921 0009 0667 0353

269 0025 0125 0979 0430 0229 0341 0498 0114 0816 0008 0980 0321

Avg lt0001 0410 0604 lt0001 0259 0322 0012 0250 0995 lt0001 0171 0027



2O




2 mmolminus1 H

2O)



DOYdagger P n

gs

Tr WUE


182 0171 0449 0532 0191 0823 0247 0236 0800 0486 0009 0428 0801

187 0079 0967 0893 0130 0753 0902 0175 0804 0915 lt0001 0103 0093

189 0933 0098 0871 0238 0232 0952 0397 0335 0931 0004 0534 0262

193 0404 0016 0511 0093 0021 0597 0110 0022 0974 0001 0848 0675

196 0034 0434 0114 0702 0991 0286 0534 0992 0003 0012 0631 0425

201 0075 0088 0474 0191 0275 0617 0362 0217 0732 0014 0928 0628

203 0018 0333 0466 0742 0511 0453 0857 0613 0466 0022 0619 0518

207 0899 0912 0378 lt0001 0480 0719 0002 0644 0421 lt0001 0120 0328

209 0082 0435 0090 0122 0844 0150 0137 0680 0212 0024 0756 0417

214 0575 0439 0223 0060 0239 0147 0073 0328 0223 0004 0796 0484

217 0794 0096 0195 0035 0395 0502 0015 0174 0549 0002 0525 0582

220 0334 0061 0985 0055 0286 0952 0121 0341 0996 0120 0444 0773

222 0034 0322 0878 0395 0407 0611 0590 0443 0729 0043 0669 0539

Avg 0003 0025 0550 lt0001 0197 0916 lt0001 0283 0794 lt0001 0996 0309



2O











2 signifi cantly
















NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy





































NT conditions


















WUE only under CT








2































































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy






























































































DOYdagger P n

gs

Tr WUE


191 0213 0857 0126 0081 0448 0445 0162 0656 0926 0071 0807 0506

196 0695 0310 0958 0008 0240 0350 0055 0335 0277 0063 0644 0310

199 0004 0253 0270 0792 0006 0655 0851 0134 0787 0028 0224 0267

203 0064 0313 0619 0008 0434 0221 0011 0417 0523 lt0001 0773 0656

206 0646 0542 0478 lt0001 0388 0302 lt0001 0491 0152 lt0001 0419 0073

210 0803 0264 0059 0014 0956 0606 0044 0810 0848 0023 0836 0620

213 0947 0356 0824 0031 0679 0940 0015 0325 0453 0002 0850 0170

217 0261 0624 0325 0039 0800 0988 0045 0818 0882 0016 0642 0524

220 0004 0862 0716 0360 0898 0530 0541 0872 0609 0001 0724 0418

Avg 0007 0944 0418 lt0001 0874 0589 lt0001 0999 0931 lt0001 0813 0556



2O




DOYdagger P n

gs

Tr WUE


196 0035 0991 0678 0942 0690 0580 0516 0720 0211 0040 0528 0336

198 lt0001 0315 0608 0229 0786 0361 0093 0433 0490 lt0001 0854 0706

202 0003 0725 0636 0851 0473 0725 0764 0394 0747 0002 0563 0159

205 0042 0839 0332 0477 0638 0220 0875 0672 0628 0001 0212 0110

210 0021 0818 0389 0002 0328 0145 0001 0123 0552 lt0001 0032 0368

212 0979 0034 0191 0032 0278 0047 0025 0516 0049 0010 0472 0088

217 0202 0036 0198 lt0001 0011 0915 0008 0256 0685 0002 0529 0437

219 0021 0627 0308 0057 0651 0858 0001 0354 0608 0001 0210 0141

224 0031 0372 0045 0001 0134 0129 0002 0557 0030 lt0001 0498 0118

226 0002 0513 0018 lt0001 0719 0006 0002 0974 0239 0006 0774 0455

Avg lt0001 0463 0424 lt0001 0467 0094 0001 0523 0424 lt0001 0929 0836



2O























2 concentrations







2 enrich-




























n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy



















































n by



























s and







4 crops





P n whereas in C















CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy


































CO2 eff ects on P

n and signifi cant














2




















In C3 plants P











































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy










































1243ndash274
























608















Environ 3513ndash25






Prod 8217ndash244


2 on root dynamshy

























elevated atmospheric carbon dioxide effects on soybean and ... · s. a. prior,* g. b. runion, h. h....

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