Diagnostics in beech exposed to chronic free-air O3 fumigation:

Ozone uptake and gas exchange responses of

adult trees

Markus Löw, A. J. Nunn, C. Heerdt, K.-H. Häberle and R. Matyssek

Climatic data

drought period of 2003

Pre dawn water potential (branches sun crown): -1.4 MPaC. Heerdt

Photosynthesis 2003 - 2004

Error bars indicate standard errorSun crown

Stomatal conductance gH2O 2003 - 2004

Error bars indicate standard errorSun crown

***

***

**

Ozone effect disappeared during drought

Stomatal conductance gH2O sun – sha 2004

Error bars indicate standard errorSun & Sha crown

***

***

**

Nighttime conductance gH2O

0.00

0.05

0.10

0.15

0.20

0.25

1xO3 sun 1xO3 sha 2xO3 sun 2xO3 sha

treatment + position

gH

2O [

mo

l m

-2 s

-1]

July 04 day

July 04 night

Sept 04 day

Sept 04 night

gH2O in % of daytime conductanceJuly September

1xO3 sun 13.97 20.641xO3 sha 11.52 14.382xO3 sun 6.63 14.472xO3 sha 26.04 19.47

Error bars indicate standard deviation

Risk of O3 injury during night is not to be neglected.

SUM0 [ppb h] 2002 20031xO3 126 1952xO3 234 358

AOT40 [ppb h] 2002 20031xO3 16 332xO3 67 117

Ozone data comparison 2002 - 2003

~50% increase

~100% increase

Calculation based on length of growing season!

Risk assessment:High „ozone threat“ in 2003?

SUM0 [ppb h] 2002 20031xO3 126 1952xO3 234 358

AOT40 [ppb h] 2002 20031xO3 16 332xO3 67 117

Ozone uptake [mmol m-2] 2002 20031xO3 18 102xO3 24 16

Ozone data comparison 2002 - 2003

~50% increase

~100% increase

~30 - 40% decrease

Due to low stomatal conductance leaves are protected from high ozone threat.

Ozone data 2003

?

?

Imaging PAM

• Portable - can be used in the tree crowns

• assess fluorescence parameters on an area basis

• non invasive stress response diagnosis

• visible leaf area 8,84 cm2 to 0,15 cm2

(max. Magnification 40x)

Area calculation and quantification

Histogram:

Image segmentation: 5 classesClass Nr of Pixels Area [cm^2] Area [%]

0-0.2 12327 0.15 4.00.21-0.4 116074 1.37 37.80.41-0.6 140635 1.66 45.80.61-0.8 35459 0.42 11.50.81-1 2705 0.03 0.9Sum 307200 3.63 100.0

Time courseMay 12, June 22, August 7, September 9

Time course IIMay 14, June 30, August 8, September 7

Overall 12 “incomplete” time lines, but 8 leaves could be followed

throughout the season

Validation by microscopy

Picture by P. Vollenweider, WSL (CH)Validated as ozone stipple

But – which stipple is it?

Microspcopy + IPAM

Conclusions I

• The high ozone regime in 2003 increased SUM0 and AOT40 strikingly.

• In 2003 stomatal conductance and photosynthesis were low because of the dry summer.

• Stomatal conductance showed a significant decrease under 2xO3 conditions in 2004.

Conclusions II

• trees were more affected by drought than by ozone in 2003

• Drought protected the leaves from severe damages by high ozone concentrations as stomata were closed.

• Ozone influx was significantly lower in 2003 than in humid years.

• High ozone concentrations per se do not cause injuries under dry conditions.

Thank You!

Black

Conductance gH2O

Error bars indicate standard error

Ozone effect decreases with prolonged drought

humid yeardrought period