towards flux-based ozone risk assessment – linking leaf gas exchange with biochemistry markus löw...

Towards flux-based ozone risk assessment

– linking leaf gas exchange with biochemistry

Markus Löw1, Manuela Blumenröther2, Karl-Heinz Häberle1, Wolfgang Oßwald2 and Rainer Matyssek1

1Ökophysiologie der Pflanzen2Fachgebiet Krankheiten der Waldbäume

Technische Universität München, Am Hochanger 13, 85354 Freising, Germany

O3 flux model at „Kranzberger Forst“

• Based on Emberson et al. (2000)

• Extended for drought conditions

• Validated for adult beech under site conditions

• Working (2002, 2003, 2004)

• Nunn et al. (2005) Env. Poll. 137(3): 494-506


• COU: cumulative stomatal ozone uptake (AFst0)

• gmax measured individually per tree and crown position

• growing season determined individually per tree and crown position

• modelled on a 10 minute basis• soil moisture function

implemented


Linear relationship in 2002 and 2004 = years without drought

End of July 2003: drought became a limiting factor

No linear relationship in 2003, so AOT40 predicts misleading high risk


Assessment of gas exchange

• Light saturated rate of photosynthesis (Amax)

• Measured during CASIROZ sampling campaigns

• Diagnostic test under „steady state“ conditions

• Licor 6400

Annual course of photosynthesis

Overall O3 effect on net CO2 uptake rate:

p = 0.04 (GLM, rep. meas.)

2004

means ± SDn = 4-5 trees


No statistically significant O3 effects in 2003

20042003

*

* *

*

Significant drought effects in 2003: 1xO3 p < 0.001; 2xO3 p = 0.02

*

*



Unusual annual course

2003 (drought year)


Error bars indicate standard errorsun crown

***

ozone effect disappeared during drought

conductance was minimal in both treatments in 2003

stomatal conductance gH2O 2003 - 2004


Unusual annual course

2003 (drought year)



„normal“ annual course

r2 = 0.57p < 0.05

2004


Ozone effect on photosynthesis




(drought year)


p < 0.05

senescencein October

(drought year)

Drought overrules ozone effect, linear correlation only during summer months

Linear correlation only in summer months (June to September)

n.s.leaf expansionin May

senescencein October


Pause

Pause

– linking leaf gas exchange with biochemistry

Measured parameters

• Phosphoenolpyruvate-carboxylase activity (PEPc)[nkat/mg protein] in sun and shade leaves

• Starch content [mg glucose equivalent/g dw] in sun and shade leaves

CO2-fixing enzyme, contributing to anaplerotic pathways, stress induced

Ambivalent results for O3 effects on carbohydrates

Activity is said to increase under O3/stress impact(Luethy-Krause et al. 1990 (Norway spruce, Scots pine);Landolt et al. 1994, 1997 (poplar, birch); Saurer et al. 1995 (birch); Fontaine 1999 (Aleppo pine); Lütz et al. 2000 (beech); Inclam et al. 2005 (Aleppo pine)...)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

May. 03 Jun. 03 Jul. 03 Aug. 03 Sep. 03 Oct. 03

date

[nk

at

mg

pro

tein

-1]

Specific PEPc activity 2003

1xO3 sun 2003 2xO3 sun 2003 1xO3 shade 2003 2xO3 shade 2003

No significant annual effect of O3 on PEPc in sun & shade leaves 2003

mv ± se

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


date

[nk

at

mg

pro

tein

-1]

Significant correlations to COU in sun & shade leaves 2003

But activity in 2xO3 leaves always lower at any given flux

R2 = 0.9619 R2 = 0.9596

R2 = 0.8195

R2 = 0.9945

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35 40

COU [mmol m-2]

[nk

at

mg

pro

tein

-1]

R2 = 0.9619 R2 = 0.9596

R2 = 0.8195

R2 = 0.9945

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35 40

COU [mmol m-2]

[nk

at

mg

pro

tein

-1]

Specific PEPc activity vs. COU 2003 (dry year!)

p < 0.05each

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


date

[nk

at

mg

pro

tein

-1]

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


date

[nk

at

mg

pro

tein

-1]

Specific PEPc activity 2004

1xO3 sun 2004 2xO3 sun 2004 1xO3 sha 2004 2xO3 sha 2004

p = 0.038

Significantly decreased PEPc activity in 2xO3 sun leaves throughout 2004

mv ± se

*

Rising activity in shade leaves is comparable to the pattern in 2003, but is not significantly

correlated to COU

2xO3 sun leaves are not responding to COU in 2004; 1xO3 sun leaves are significantly negative

correlated to flux

R2 = 0.0881

R2 = 0.9341

R2 = 0.626

R2 = 0.6573

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 10 20 30 40

COU [mmol m-2]

sp

ec

. ac

tiv

ity

[n

ka

t m

g p

rote

in-1

]

R2 = 0.0881

R2 = 0.9341

R2 = 0.626

R2 = 0.6573

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 10 20 30 40

COU [mmol m-2]

sp

ec

. ac

tiv

ity

[n

ka

t m

g p

rote

in-1

]

Specific PEPc activity vs. COU 2004

p < 0.01

Chronic effects of O3 result in decreased PEPc activity

0

5

10

15

20

25


date

[mg

glc

eq

uiv

ale

nt

g d

w-1

]

0

5

10

15

20

25


date

[mg

glc

eq

uiv

ale

nt

g d

w-1

]

Starch concentrations in leaves 2003 (dry year)

1xO3 sun 2003 2xO3 sun 2003 1xO3 shade 2003 2xO3 shade 2003

Significantly decreased starch contents in 2xO3 sun leaves throughout May, June & July

p = 0.023

mv ± se

*allocationprocesses

0

5

10

15

20

25


date

[mg

glc

eq

uiv

ale

nt

g d

w-1

]

Starch concentrations in leaves 2004

1xO3 sun 2004 2xO3 sun 2004 1xO3 sha 2004 2xO3 sha 2004

Higher starch levels in 2004Significantly reduced starch contents in 2xO3

sun

p = 0.009

Carbohydrates used for repair/detoxification processes in 2xO3 sun leaves?

Less photosynthetic products available under 2xO3?

**allocationprocesses

mv ± se

0

20

40

60

80

100

0 5 10 15 20 25 30COU [mmol m-2]

rela

tiv

e s

tarc

h, A

ma

x [

%]

0

20

40

60

80

100

0 5 10 15 20 25 30COU [mmol m-2]

rela

tiv

e s

tarc

h, A

ma

x [

%]

1xO3 = 100%

0

20

40

60

80

100

0 5 10 15 20 25 30COU [mmol m-2]

rela

tiv

e s

tarc

h, A

max

[%

]

Relative starch and Amax vs. COU in sun leaves 2004

r2 = 0.738p < 0.05

Annual response patterns of Amax and starch to O3 are significantly correlated

starch Amax

Conclusions I• O3 flux model for adult beech trees in

„Kranzberger Forst“ validated & ready to use

• Discrepancy between O3 exposure and uptake especially in dry year

• Significant O3 effect on photosynthesis only in 2004

• Significantly reduced starch concentrations in sun leaves 2003 and 2004; differences between O3 regimes more pronounced in 2004

• Significant correlation of PEPc activity and COU

• Biochemical parameters indicate a chronic O3 effect

• Controversial results for PEPc indicate the need for more studies on adult trees….

Conclusions II• Drought overrules O3 impact in 2003

• Different parameters (starch + Amax) show similar responses to O3

• Risk assessment does profit from the combination of several parameters from different scaling levels

• Thus, these parameters should be included in Flux modelling (Flux + defence)

Acknowledgements

The present study is part of the Project "CASIROZ – The carbon sink strength of beech in a changing environment: Experimental risk assessment by mitigation of chronic ozone impact", which is supported by European Commission - Research Directorate-General, Environment Programme, "Natural Resources Management and Services" (EVK2-2002-00165, Ecosystem Vulnerability).

Pierre Dizengremel, UHP Nancy, France

Frank FleischmannTina Schmidt

Angela NunnThorsten Grams

Thomas Feuerbach...

towards flux-based ozone risk assessment – linking leaf gas exchange with biochemistry markus löw...

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