New stable isotopic techniques to investigate links between terrestrial carbon and water cycles

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New stable isotopic techniques to investigate links between terrestrial carbon and water cycles

Margareth Barbour, Lisa Wingate, Jérôme Ogée

To cite this version:

Margareth Barbour, Lisa Wingate, Jérôme Ogée. New stable isotopic techniques to investigate links between terrestrial carbon and water cycles. Canopy processes in a changing climate, International Union of Forest Research Organisations (IUFRO). AUT., 2010, Victoria and Tasmania, Australia. 31 p. �hal-02819143�

Emerging Technologies

New stable isotopic techniques to investigate links between terrestrial carbon and water cycles

• *University of Cambridge, UK

• ⁺INRA, France

Margaret Barbour, Lisa Wingate* and Jérôme Ogée⁺

Outline

› Stable isotopes and plants

› New measurement techniques

› New understanding gained recently using lasers

- Mesophyll conductance

- The importance of leaf respiratory biochemistry to ecosystem δ¹³CO₂ - Tracing carbon through ecosystems using stable isotopes

- Disequilibria in C¹⁸O¹⁶O between leaf and soil isofluxes

› PrometheusWiki

2

Photosynthetic

C discrimination

› Rubisco discriminates against ¹³C during

photosynthesis

› Degree of discrimination depends on supply of and demand for CO₂

› δ¹³C of C3 plants depends on stomatal conductance and photosynthetic rate (WUE)

CO₂ Partial pressure (ca) Isotope ratio (δ¹³Ca)

Kinetic fractionation a (4.4‰)

CO₂ Partial pressure (ci)

Biochemical fractionation

b (27‰)

δ¹³Cp = δ¹³Ca – a – (b – a)ci/ca ci/ca

-28 δ¹³C -29

Oxygen isotope theory

› H₂¹⁸O evaporates and diffuses more slowly than H₂¹⁶O

› Leaf water becomes enriched in H₂¹⁸O

› Degree of enrichment depends on evaporative environment (humidity, temperature, stomatal conductance)

› Enrichment is passed on to organic molecules

› Enrichment also passed on to CO₂

4

H2O

Partial pressure (ea) Kinetic fractionation Isotope ratio (δ¹⁸Ov)

εk (28.5‰)

H2O

Partial pressure (ei)

Vapour pressure fractionation ε* (≈ 9‰)

δ¹⁸Oe = δ¹⁸Os + ε* + εk + (δ¹⁸Ov – δ¹⁸Os – εk)ea/ei

29 O in H2O (+27‰) O in CHO δ¹⁸Op

H2O 28

Soil water (δ¹⁸Os) ea/ei

Ecosystem isofluxes to partition net fluxes

Linking

biogeochemical

cycles

Tunable diode laser absorption spectrometer

› TDL is based on absorption of infrared (IR) energy following Beer’s law.

› A diode laser is tuned to

quantify two or three individual absorption lines

› Low temperature and pressure

› On-line, real-time

measurements, high temporal resolution

› Frequent calibration

› Can be used in field (liquid N₂!)

6

Wavelength-scanned cavity ring down spectrometer

› CRDS is based on absorption of near-infrared energy following Beer’s law

› Reflection within cavity provides 20km pathlength

› Wavelength monitor measures time-based decline in specific absorption features (¹²CO₂ and

13CO₂)

› Less frequent calibration

› Usually lower temporal resolution

› Portable

in out

concentration

δ¹³C δ¹⁸O

Real-time display

What difference do lasers make?

› 5 samples per night to construct 1 Keeling plot to give 1 ecosystem respiration value

› Whole study over 16 nights had 80 air samples

› Analysis on IRMS took 27 hours and cost

$4,000 (mates rates)

2005

What difference do lasers make?

Rapid changes in δ¹³C of ecosystem-respired CO₂ after sunset are consistent with transient ¹³C enrichment of leaf respired CO₂.

Barbour et al. in review

› 960 samples per night to construct 120 Keeling plots to give 120 ecosystem respiration values

› Whole study over 28 nights had 26,880 air samples

› Analysis on IRMS would have taken one year and cost $1.3M

› OR 2 years if include all daytime analyses (cost $2.6M)

› Lasers cost US$70,000 to US$150,000

10

2010

Linking C and H

O cycles using

13

CO

, C

O

O and H

O

•Do we have high enough temporal resolution?

YES

•Can we accurately model component isofluxes?

YES for leaves

YES (with CA activity) for soils

•Are the component isofluxes different enough to allow partitioning?

YES for C¹⁸O¹⁶O OFTEN for ¹³C

SOMETIMES for H₂¹⁸O

•Can we measure ecosystem isofluxes?

YES for ¹³CO₂ (especially short-stature canopies) YES for H₂¹⁸O

SOMETIMES for C¹⁸O¹⁶O

The full potential of isoflux interpretation is not yet realised,

But we have learned lots of cool things along the way...

12

New understanding of

mesophyll conductance

New understanding of mesophyll conductance

14

Several resistances to diffusion of CO₂ from the sub-

stomatal cavity to the sites of fixation

Gaseous and liquid phase Cell walls

Plasma membrane Cytosol

Chloroplastic membrane

Measuring g

using ∆

C

› Use standard gas exchange to calculate C_i/C_a

› Calculate ∆¹³C assuming infinite g_m (C_c = C_i)

› Compare with measured ∆¹³C

› Big difference = low g_m

› Small difference = high g_m

14 16 18 20 22

14 16 18 20 22

low g

m

high g

m

∆13 C observed (‰)

Genotypic variability in g

: Barley

16

Dash Omaka GP4 GP2 HB4 HB2

0.0 0.1 0.2 0.3 0.4 0.5

g m (mol CO 2 m-2 s-1 )

Genotype

Barbour et al. 2010, PC&E 33, 1176-1187

g

can respond rapidly and reversibly to changes in irradiance

0 5 10 15 20 25

0.0 0.2 0.4 0.6 0.8 1.0

0 50 100 150 200

0.0 0.1 0.2 0.3

PAR = 400 PAR = 1800

PAR = 1800

A

(µmol m^-2 s^-1)

g_s (mol m^-2 s^-1)

Time (minutes) g_m

(mol m^-2 s^-1) 0.219 +/- 0.005

0.137 +/- 0.003

0.201 +/- 0.004

Genetic variability in the degree of responsiveness of

to light and [CO

]

18 0.0

0.1 0.2 0.3 0.4

Responsive genotypes Less responsive genotypes

gm (mol m-2 s-1 )

PAR (_µmol m^-2 s^-1) 1980 1130 460

Dash HB4 HB2 Omaka Retriever

0.0 0.1 0.2 0.3

gm (mol m-2 s-1 )

Genotype

Ca (ppm) 320 650

5 cereal genotypes tested Response in

other species???

High g_m + low g_s = high WUE

Leaf respiratory

biochemistry is important in ecosystem

CO

flux

with

John Hunt and Johannes Laubach Landcare Research, New Zealand Guillaume Tcherkez, Uni Paris

δ¹³

C

reveals dynamics of leaf respiratory biochemistry

20 0.0

0.5 1.0 1.5 2.0 2.5

0 5 10 15 20 25 30

-30 -25 -20

Light-enhanced dark respiration

High light Low light

Respiration rate (µmol m-2 s-1 )

13C-enriched organic acids On-line, real-time leaf-respired CO

2

δ13 C R (‰)

Time since start of dark period (mins)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0 1 2 3 4 5 6 7 8

Light level Low Medium High r² = 0.83

13 C enrichment during LEDR (‰)

LEDR peak height (µmol m^-2 s^-1)

Highly enriched respiration during LEDR is likely due to organic acid substrates, including malate.

Barbour et al. 2007; Gessler et al. 2009

In a cereal model plant:

CO₂ respired at the beginning of the dark period is enriched in ¹³C

δ

C

is enriched just after sunset

...even when only above-canopy intakes are used

0.7 0.8 0.9 1.0 1.1 1.2 1.3

-30 -29 -28 -27 -26 -25 -24

δ13 C eco (‰)

Full profile

Above canopy only

Effect is more pronounced after sunny days

22

0.0 0.5 1.0 1.5 2.0

-30 -29 -28 -27 -26 -25 -24

*

*

**

**

*** **

δ13 C Reco (‰)

Time (hours after sunset)

Sunny Cloudy

Tracing carbon through ecosystems

Tracing carbon through ecosystems

› Photosynthetic ¹³CO₂ discrimination varies with environmental

conditions

› Natural tracer for carbon flux through ecosystems

› TDL has sufficient temporal

resolution to allow measurement of photosynthetic discrimination, δ¹³C of leaf, stem and below-ground respiration, and whole ecosystem isofluxes

› Mature maritime pine forest in France

› Wingate et al. 2010 (New Phytologist 188, 576-589)

24

Photosynthetic discrimination against

CO

Transport speed of recently fixed

δδδδ

C

Wingate et al. NP, 2010

Disequilibria in C

O

O between leaf and soil isofluxes

Seasonal C

O

O discrimination

28

soil moisture [m3 m-3 ]Gross flux signatures [‰VPDB-CO 2]

Day of 2007 relative humidity [%] δδδδ¹⁸O signals of leaf and soil gross fluxes over the season

leaf day

soil day/night

leaf night

Summary

›

New laser spectrometers have very high temporal resolution

›

Have allowed a number of advances including

Dynamic mesophyll conductance

-

Importance of rapid changes in leaf biochemistry to ecosystem flux

-

Evidence of variable speed of carbon flow through forest ecosystems

-

Proof of disequilibria between leaf and soil C

O

O isofluxes

›

Now poised to partition ecosystem fluxes and to link C and H

O cycles

30

http://prometheuswiki.publish.csiro.au/

http://prometheuswiki.publish.csiro.au/

Editorial board

• Margaret Barbour, University of Sydney

• Brendan Choat , The Australian National University

• Will Cornwell, University of California, Berkeley

• John Evans, The Australian National University

• Jen Funk, Chapman University

• Bob Furbank, CSIRO Plant Industry

• Hans Lambers, University of Western Australia

• Rana Munn, CSIRO Plant Industry

• Adrienne Nicotra (EiC), The Australian National University

• Lawren Sack, University of California, Los Angeles

• Lou Santiago, University of California, Riverside

• Frank Sterck, Wageningen University Editorial board

• Margaret Barbour, University of Sydney

• Brendan Choat , The Australian National University

• Will Cornwell, University of California, Berkeley

• John Evans, The Australian National University

• Jen Funk, Chapman University

• Bob Furbank, CSIRO Plant Industry

• Hans Lambers, University of Western Australia

• Rana Munn, CSIRO Plant Industry

• Adrienne Nicotra (EiC), The Australian National University

• Lawren Sack, University of California, Los Angeles

• Lou Santiago, University of California, Riverside

• Frank Sterck, Wageningen University