Effects of rising CO2 concentration on water use efficiency of

Eucalyptus saligna

Craig Barton

M. Adams , J. Conroy, R. Duursma, D. Eamus, D. Ellsworth, S. Linder, B. Medlyn, D. Tissue, R. McMurtrie

CCRSPI Conference 2011, Melbourne

Hawkesbury Forest Experiment Established to investigate the impacts of climate change on Australian

trees. Integrated program of experimental research and modelling. Little known about the response of Eucalypts to elevated CO2.

Many Australian forest and woodland systems characterised by poor soils and frequent droughts.

Stomatal conductance response to elevated [CO2]

0

0.2

0.4

0.6

0.8

1

1.2

conifers deciduous eucalyptus

n = 12 n = 22 n = 4

g s(E

leva

ted)

: gs

(Am

bie

nt)

Medlyn et al unpublished

Whole Tree Chambers

Designed and first used in Northern Sweden.

They isolate trees in a controlled environment for CO2 exposure and whole-tree measurements.

Chambers track outdoor conditions.

Allows us look at interactive effects of elevated CO2 and drought.

Growing under local climate.

Eucalyptus saligna

Sydney Blue Gum Fast growing mainly coastal tree that has

commercial plantation use. Prefers warm humid climatic conditions Mean precip 900-1800mm p.a. Planted April 2007.

Experimental design

12 whole tree chambers 6 run at ambient [CO2] A (390 ppm)

6 run at elevated [CO2] E (630 ppm)

Half of each set subjected to periodic drought.

One year old

1.5 years old - Extended to 9m tall

2 years old – Harvested trees

Whole tree chambers

Fresh air inlet 1 air change per hour

Root barrier

Heat exchanger

floor

6 m

condensate

CO2 addition

Described in Medhurst et al 2006 PC&E and Barton et al 2010 Ag.For. Met

Whole-tree fluxes

-100

-50

0

50

100

150

200

29-Mar 29-Mar 29-Mar 29-Mar 29-Mar 30-Mar 30-Mar 30-Mar 30-Mar 30-Mar 31-Mar

CO

2 F

lux

(u

mo

l m-2

s-1

tre

e-1

)

0

500

1000

1500

2000

2500

3000

PA

R (

um

ol m

-2 s

-1)

wtc2-E

wtc7-A

PAR

-5

0

5

10

15

20

25

30

35

40

45

29-Mar 29-Mar 29-Mar 29-Mar 29-Mar 30-Mar 30-Mar 30-Mar 30-Mar 30-Mar 31-Mar

H2

O F

lux

(m

mo

l m-2

s-1

tre

e-1

)

0

1

2

3

4

5

6

7

8

9

10

VP

D (

kP

a)

wtc2-E

wtc7-A

VPD

A

B

The system can resolve responses to short term fluctuations in light.

Afternoon depression of carbon uptake present.

CO2 fluxes are very similar

Water loss is much lower in the elevated CO2 tree.

Barton et al 2010 Agricultural and Forest Meteorology 150:941-951

Whole canopy CO2 flux per unit leaf area

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Ave

rage

CO 2

Flu

x (

mo

l m-2

s-1)

0

2

4

6

8

10

A

EA

Whole canopy H2O flux per unit leaf area

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Ave

rage

H2O

Flu

x (m

mo

l m-2

s-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

AE

VPD in chambersApril 08 – March 09

0 1 2 3 4 5

01

23

45

Mean VPD (2-hourly) in AmbientCO2chamberskPa

Mea

n V

PD

(2-

hour

ly)

in E

leva

tedC

O2c

ham

bers

kP

a

Effect of CO2 on Instantaneous Transpiration Efficiency ITE = instantaneous transpiration efficiency

= A / E (mmol CO2 mol-1 H2O)

Carbon Assimilation / Water used

According to Ball-Berry model, A and E are related:

Implications

If we assume that stomatal conductance does not acclimate to [CO2] then the ratio of ITEelev / ITEamb will equal Ca-elev / Ca-amb

In our case 630/390 = 1.6 ITE should increase by 60%

11

ka

Dg

C

E

A

Leaf level ITE

y = 1.6127x

R2 = 0.7932

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12

Leaf level ITE (ambient)

Leaf

leve

l IT

E (

elev

ated

)

ITE

Linear (ITE)

Data from D.Ellsworth

Transpiration Efficiency

0 1 2 3 4 5

01

02

03

04

05

0

VPD in WTC (kPa)

AE

mo

lCO

2m

mo

lH2O

Ambient 2hr meanElevated 2hr mean

1.14 1.49 1.59 1.68 1.6 1.55 1.51 1.26 1.71 1.52Treatment ratios:

0 1 2 3 4 5

01

02

03

04

05

0

VPD in WTC (kPa)

AE

mo

lCO

2m

mo

lH2O

Ambient 2hr meanElevated 2hr meanAmbient VPD bin meanElevated VPD bin mean

1.14 1.49 1.59 1.68 1.6 1.55 1.51 1.26 1.71 1.52Treatment ratios:

Transpiration Efficiency

Assimilation

0 1 2 3 4 5

05

10

15

VPD in WTC (kPa)

Ass

imila

tion

m

olC

O2

m2 le

af

sAmbient 2hr meanElevated 2hr meanAmbient VPD bin meanElevated VPD bin mean

1.04 1.09 1.08 1.22 1.33 1.42 1.46 1.46 1.73 1.85Treatment ratios:

Transpiration

0 1 2 3 4 5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

VPD in WTC (kPa)

Tra

nsp

ira

tion

mm

olH

2O

m2 le

af

sAmbient 2hr meanElevated 2hr meanAmbient VPD bin meanElevated VPD bin mean

0.98 0.79 0.73 0.76 0.84 0.91 0.95 1.09 1.05 1.12Treatment ratios:

Conclusions

Strong down-regulation of photosynthesis resulting in little if any “fertilisation effect” of elevated CO2

Data supports Ball-Berry model at leaf and canopy scale.

No acclimation of stomatal response to CO2

Implications for models used to predict forest growth (3PG, GDAY, Cabala)

VPD is important to results.

Investigating the Impacts of Climate Change on Australia’s Forests

Craig Barton

M.Adams, B. Amiji, J. Conroy, R. Duursma, D.Eamus, D. Ellsworth, S. Linder, M. Löw, B. Medlyn, J. Parsby, D. Tissue, R. McMurtrie, et al