lecture for ‘biogeochemistry and global change’ lowland ...aibrom/bggc/lecture veldkamp effects...
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Effects of N-deposition on tropicallowland and montane forests
Lecture for ‘Biogeochemistry and Global Change’
Edzo Veldkamp
Are tropical forests Nitrogen or Phosphoruslimited?
How is the internal N- Cycle affected by theabundance of Nitrogen in P-limited tropicallowland forests?
What will happen to tropical forests if the depositionof nitrogen-containing compounds will increase in thefuture?
Soil Scientist‘s view:
Trop. Lowland forest
Trop. Montane forest
Trop. Lowland 'Podzol'
Temperate forest
N in Litterfall (kg ha-1 yr-1)
0
40
80
120
160
200
0 50 100 150 200 250
Based on Vitousek (1984)
Are tropical forests N limited?D
ry m
ass/
N r
atio
0
2
4
6
8
10
12
14
16
18
0 0,5 1 1,5 2 2,5N Concentration in litterfall (% dry mass)
Trop. Lowland Forest
Trop. Montane Forest
Based on Vitousek (1984)
Does nitrogen control fine litter fall?Li
tter
dry
mas
s (M
g ha
-1 y
r-1 )
• Most lowland tropical forestsdo not have efficient within-stand nitrogen economiescompared to temperate forests.
• The few tropical forestswith an efficient within-standnitrogen use are eithermontane forests or arelocated on podzols
Indirect evidence shows that:
Also direct evidence startsto emerge with fertilizationexperiments
Trop. Lowland forest
Trop. Montane forest
Trop. Lowland 'Podzol'
Temperate forest
00 2 4 6 8 10 12 14 16
P in Litterfall (kg ha-1 yr-1)
2000
4000
6000
8000
Based on Vitousek (1984)
Are tropical forests P limited?D
ry m
ass/
P ra
tio
Trop. Montane Forest
0
2
4
6
8
10
12
14
16
18
0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08
P. concentration in litterfall (% dry mass)
Trop. Lowland Forest
Based on Vitousek (1984)
Does phosphorus control fine litter fall?Li
tter
dry
mas
s (M
g ha
-1 y
r-1 )
• Many (but not all!!) lowlandtropical forests have moreefficient within-standphosphorus economies thanmost temperate forests.
•The tropical forests withthe most efficient within-stand phosphoruseconomics include some ofthe montane forests
Why are within-stand P-economy of tropical lowlandforests more efficient than most temperate forests?
•Endproduct of chemical weatheringin humid tropics are sequioxides,which can bind Phosphorus almostirreversible
•Phosphorus content of a site cannotbe replenished by the fixation of anabundant gas like is the case forNitrogen
Source: UNEP
Source: ISRIC
How much tropical rainforest is situated on soils withsesquioxides?
•Most lowland tropical forests are P limitedbecause they are situated on old, heavily weatheredtropical soils which contain sesquioxides
•P-limited lowland tropical forests normally have anexcess of Nitrogen
•How is the internal N-Cycle affected by the relativeexcess of Nitrogen in P-limited tropical lowland forests?
N2O NOx
Gaseous losses
LeachingClay minerals
NO2- NH3
NH4+
NO3-
Soil Organic Matter
Organisms
Residues,Manures
N2
Nitrification Denitrification
N cycling in soils
NO3- N2NH4
+
NO N2ONO N2O
OrganicMatter
Firestone & Davidson, 1989
•The trace gasses NO and N2O are linked throughtheir common processes of microbial production.
•NO + N2O emissions are correlated with the rateat which Nitrogen cycles through the ecosystem.
NO + N2O emissions should covary with indexesof nitrogen availability.
NO + N2O emissions should be high in tropicallowland forests
--------------------Tg N y-1 -----------------•Natural sources
Ocean 3.0 (1-5)Tropical forest soils 3.0 (2.2-3.7)Tropical savanna soils 1.0 (0.5-2.0)Temperate forest soils 1.0 (0.1-2.0)Temperate grasslands 1.0 (0.5-2.0)
•Anthropogenic sourcesAgricultural soil 3.3 (0.6-14.8)Biomass burning 0.5 (0.2-1.0)Industrial Sources 1.3 (0.7-1.8)Cattle and feedlots 2.1 (0.6-3.1) Σ 16.2 (6.4-34.4)
•Sinks Atmospheric Increase 3.9 (3.1-4.7)Soils ?Stratospheric Sink 12.3 (9-16) Σ 16.2 (12.1-20.7)
Global N2O budget (IPCC, 1997)
Log Y = -0,0563X + 2,331
R2 = 0,70
Sum of annual estimates of NO + N2O emissions as afunction of litterfall C/N
-1,5
-1
-0,5
0
0,5
1
1,5
10 20 30 40 50 60 70
Litterfall C/N (Davidson et al, 2000)
Log(
NO
+ N
2O) f
lux
(kg
N h
a-1 y
r-1 )
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250
N in Litterfall (kg ha-1 yr-1)
Trop. Lowland Forest
Trop. Montane Forest
Trop. Lowland 'Podzol'
Possible relation between annual litterfall N and sum ofannual NO + N2O emission
Pred
icte
d N
O +
N2O
flu
x (k
g N
ha-
1 yr-
1 )
•The low efficiency of within-stand nitrogen economies oftropical lowland forests lead tohigh emissions of NO + N2O.
•I speculate that tropicalmontane forest will have lowNO + N2O emissions becauseof their relatively efficientwithin-stand nitrogeneconomy
•What will happen to tropical lowland forests ifthe deposition of nitrogen-containing compoundswill increase in the future?
Legume crops
Fossil fuel
N fertilizer
1970 1980 1990Year
19600
20
40
60
80
100
120
140
160
Terr
estr
ial N
-fixa
tion
Tg N
yr-1
Range of estimates ofnatural N fixation
Galloway et al., (1995)
Comparison of natural and human-drivenNitrogen sources
0
20
40
60
80
100
120
Tg N
yr-1
20
40
60
80
100
120
Present 20200
Present 2020
Tg N
yr-1
Temperate area
FertilizerEnergy
Tropical area
Present and future anthropogenic N production
Adapted from Galloway et al., 1995
Increasing N deposition is already happening!
0
1
2
3
4
5
6
7
8
9
Banana Plantation Agriculture in temperateareas
N2O NO
N2O
and
NO
loss
es (%
of
appl
ied
fert
ilize
r
Adapted from Veldkamp & Keller 1997
Hall & Matson, 1999
N2O & NO emissions from soil in N-limited and P-limitedtropical forests before and after N addition
•P-limited forest lostmore NO + N2O than N-limited forest
•P-limited forests seemto be less able to retainanthropogenic N as N-limited forests
0
5
10
15
20
25
-7 0 7 14
N limited
N2O
-N (n
g cm
-2 h
-1)
0
5
10
15
20
25
30
-7 0 7 14
N limited
NO
-N (n
g cm
-2 h
-1)
N a
dditi
onN
add
ition
0 7 14
P limited
0 7 14
P limited
N a
dditi
onN
add
ition
•Increasing N deposition in lowland tropicalforests will almost certainly lead to even higherN-trace gas (NO + N2O) emissions as theseecosystems seem to be less able to retainanthropogenic N than temperate forests
•Increasing energy production and fertilizeruse will lead to higher N deposition in thetropics in the near future