Stable isotope (13C) analyses of vegetation across Australia

Derek EamusRizwana RummanTomek Wyczesany

with the co-operation of many Supersite Managers across Australia

The Australian Supersite Network

Site descriptionsVeg Rainfall

(mm)Temp (oC)

Litchfield NT Savanna 1700 23 - 32

Far N Qld Simple notophyll vine forest 2000 + 23 - 29

Alice Springs NT Mulga (Acacia anuera) 300 14 - 30

SE Qld (peri-urban) a mix of dry eucalypt forest and wet heath

1000 15 - 26

WA mosaic of temperate woodland, heathland and mallee vegetation

245 11 - 25

Tumburumba wet eucalypt forest 900 5 - 20

Victoria dry eucalypt forest 675 7 - 18

Tasmania tall closed eucalypt forest 600 12 - 27

SA Undulating mallee woodland ; Calperum Mallee

225 10 - 25

Aims of the study

• Examine seasonal and spatial variability in WUE across Australia

• Examine niche separation of co-occurring species• Determine the relative contributions of

differences in A and gs to differences in WUEi across species and sites (needs Δ18O data of cellulose)

• Determination of plant functional types based upon stable isotope analyses

Extracting water (for deuterium and 18O analyses) from soil and stem segments

using cryo-distillation

Picarro analysers for water and C stable isotope analyses

Carbon Isotope Discrimination• Why do plants contain less 13C in their leaves than the CO2 in

the air?

1. 13CO2 diffuses into leaves more slowly than 12CO2

2. Rubisco preferentially binds 12CO2

δ13Cplant = δ13Catm - (diffusion effect + enzyme effect)

Discrimination

Summary

• The δ13C of C3 plants reflects how much stomatal conductance limits photosynthesis.

δ13Cplant, ‰

C3 plants C4 plants

Source: Cerling et al., 1997

lessstomatal limitation

morestomatal limitation

ci ≈ ca; ci/ca=1

Less δ13CMore Δ

Smaller WUEi

ci << ca; ci/ca<1

More δ13CLess Δ

Larger WUEi

Source: Werner et al, 2012, Cerling et al., 1997

Carbon Isotope Discrimination• Farquhar, Ehleringer and Hubick (1989), proposed the

equation for carbon isotope discrimination:

a = Diffusion effect (the rate of diffusion of 13CO2 across stomatal pore from atmosphere to leaf is lower by a factor of ~4.4‰ than 12CO2)

a

i

c

caba )(

b = Isotope effect caused by preference of Rubisco for 12CO2 over 13CO2 ~27 ‰

Ca

CO2

Ci

H2O

wi

wa

gc gw

• Carbon isotope discrimination is a measure of intrinsic water-use-efficiency (WUEi)

Intrinsic Water-Use-Efficiency

WUEi is the ratio of carbon assimilation to stomatal conductance (A/gw)

Photosynthesis, A = gc (ca-ci)

WUEi = A/gw = gc (ca-ci)/gw

Source: Werner et al, 2012

• Environmental factors, such as water availability, cause variations of ci/ca, mainly through their effects on stomatal conductance and photosynthetic activity

• This effect is measurable as either an increase in ∂13Cleaf or as a decrease in Δ (= increased WUEi)

• Intrinsic WUE (WUEi) for C3 plants is given by:

NSW data (2 spp per site) + Alice Springs Supersite + Robson Creek + GDE River Red Gum

0 500 1000 1500 2000 2500

-34

-32

-30

-28

-26

-24

-22

-20

f(x) = − 0.00246231776649395 x − 25.7523421802913R² = 0.669935749125165

Annual rainfall (mm)

δ13C

Robson Creek (FNQ)

River Red Gum, Alice Springs - using GW – thinks it is receiving 1800 mm of rainfall

Alice Springs

New South Wales data

Comparing our data with Miller et al. 2001 (NT gradient) and Schulze et al. (1998; Qld gradient):

0 500 1000 1500 2000 250012

14

16

18

20

22

24

26

28

30

f(x) = 1.07920788410703 ln(x) + 12.6144822622165R² = 0.630528196413374

f(x) = 0.00203908242593683 x + 18.1725606055032R² = 0.701306236736437

f(x) = 0.00259110761070775 x + 18.213158684251R² = 0.670777187857475

Annual rainfall (mm)

Del

ta (%

o)

Comparing our data with Stewart et al. 1995 (S Qld)

200 400 600 800 1000 1200 1400 1600 1800

-32

-30

-28

-26

-24

-22

-20

f(x) = − 0.00243482644921668 x − 25.774638943141R² = 0.330022019446409

Annual rainfall (mm)

δ

13C

(%o)

What can we do with δ13C data?

• Can use δ13C to calculate Δ (discrimination) since:

Δ = (-8- δ13C )/(1+ δ13C /1000)

• Can calculate WUEi and Ci/Ca from this:

WUEi = (Ca*(27- Δ ))/(1.6*(27-4.4))

Ci/Ca = (Δ -4.4)/(27-4.4)

WUE gradient across TERN Supersites

Using eddy covariance data available in the Supersites to compare ecoWUE and stable isotope assessments of WUEi

Recent studies show that:

Ecosystem instantaneous water-use-efficiency ecoWUEinst and ecosystem intrinsic water-use-efficiency ecoWUEi are responsive to changes in soil moisture content and leaf-to-air VPD (Vickers et al. 2012)

an assessment at canopy-scales will enable the comparison across contrasting communities (Campos et al. 2013)

WUEi across multiple sites

0 500 1000 1500 2000 25000

10

20

30

40

50

60

70

80

90

100

f(x) = − 0.0257964253278425 x + 87.4796148691821R² = 0.670777187857474

Mean annual rainfall (mm)

Intr

insi

c w

ater

-use

-effi

cien

cy

Example of application of stable isotope analyses: Ecohydrological niche separation

Can we identify contrasting strategies for water-use among co-existing plant species?

– Moreno-Gutierrez et al 2012: δ13C used to disaggregate 10 co-occurring species along an ecophysiological gradient

– Combined δ13C and Δ18O revealed a wide spectrum of degree of stomatal regulation of A

– This correlated with WUEi and coexisting species maintained their species specific isotopic niches that reflect ecohydrological niche segregation

Niche separation ? Variation in δ13C within a site across species is as large as across sites across a

rainfall gradient – data from FNQ

Alphitonia whitei Litsea leefeana Unknown. Flindersia? Elaeocarpus grandis Flindersia pimenteliana Schefflera actinophylla

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

δ13C

%o

Example of application of stable isotope analyses: Plant Functional Type Analyses

Can we identify contrasting plant functional types using Δ13C ?

– Werner and Maguas 2010: Compared Δ13C of across 11 species of contrasting PFT

– Found pronounced and consistent variation in Δ13C across PFTs – correlated with phenology, leaf attributes (SLA, foliar N)

– Principal component analyses showed Δ13C to be as good a predictor of PFT as using multiple leaf traits.

Current data gaps

• Samples from different PFTs

• Wide selection of species across a site

• Δ18O of leaf cellulose to disaggregate effects of gs from A

The ENDThanks for listening and any

questions?

Conclusions

• Do species matter?

Brief site descriptions• Litchfield Savanna: tall open eucalypt savanna in a tropical wet-dry climate; mean

annual min/max temp of 23–32 oC; annual rainfall of 1700 mm

• FNQ Rainforest: a simple notophyll vine forest in a tropical wet climate; mean annual min/max temp of 23–29 oC ; annual rainfall of 2000+ mm

• Alice Mulga: open Mulga woodland savanna in a semi-arid climate; mean annual min/max temp of 14–30 oC; annual rainfall of 275 mm

• SEQ Peri-urban: a mix of dry eucalypt forest and wet heath in a subtropical climate; mean annual min/max temp of 15–26 oC; annual rainfall of 1000 mm

• Great Western Woodland: a mosaic of temperate woodland, heathland and mallee vegetation in a semi-arid climate; mean annual min/max temp of 11–25 oC; annual rainfall of 245 mm

• Tumbarumba Wet Eucalypt: wet eucalypt forest in a temperate climate; mean annual min/max temp of 5–20 oC; annual rainfall of 900 mm

• Victorian Dry Eucalypt: dry eucalypt forest is a temperate climate; mean annual min/max temp of 7–18 oC; annual rainfall of 675 mm

• Warra Tall Eucalypt: a tall closed eucalypt forest in a temperate climate; mean annual min/max temp of 12–27 oC; annual rainfall of 600 mm

• Cumberland Plain EucFace: remnant eucalypt woodland in a temperate climate; mean annual min/max temp of 11–24 oC; annual rainfall 700 mm

• Calperum Mallee: an undulating mallee woodland in a semi-arid climate; mean annual min/max temp of 10–25 oC; annual rainfall of 225 mm