co2drivenincreasesinvegetaon+ cover 2 - land talk 2... ·...

CO2-‐driven increases in vegeta1on cover Randall Donohue, Mike Roderick1,2, Tim McVicar, Graham Farquhar1. CSIRO Land and Water

1 Research School of Biology, The Australian National University 2 Research School of Earth Sciences, The Australian National University

Understanding CO2’s role in global greening •  Laboratory and plot-‐based studies have shown that elevated CO2 concentra>ons generally increase plant produc>vity and – under water-‐stressed condi>ons – foliage cover

•  Satellites have shown that foliage cover has been increasing globally over the past few decades

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•  Due to climate variability it has been difficult to quan>fy the role that elevated CO2 has played in this greening, especially over warm, dry environments

Relative change in foliage cover, 1982-2010

CO2 fer>lisa>on | Donohue Roderick McVicar Farquhar

Donohue, Roderick, McVicar, Farquhar (2013). The impact of CO2 ferBlisaBon on maximum foliage cover across the globe's warm, arid environments, GRL (40) 1-‐5.

CO2 fer1lisa1on

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d d d d1 d2

ph a l l

ph a l l

W C A EDW C D A E

= − = −

•  In rela>ve terms, the change in Wph is

Wph Al El Ca D

water use efficiency of photosynthesis carbon assimila>on rate [per unit leaf area] evapora>on (transpira>on) rate [per unit leaf area] atmospheric CO2 concentra>on water vapour pressure gradient between leaf and atmosphere; approximated as the Vapour Pressure Deficit

Al El

CO2 H2O

ph l lW A E=

•  Elevated CO2 increases the water use efficiency of photosynthesis, Wph


CO2 fer1lisa1on across our study region

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Warm, dry landscapes free from irriga>on and surface water features, and with high quality precipita>on data

Growth condi>ons P (m a-‐1)

dP/P (%)

D (kPa)

dD/D %

F dF/F (%)

Terrestrial globe 0.82 5.6 0.89 10.5 0.45 8.7

Water-‐limited 0.36 10.0 1.50 8.2 0.22 14.4

Analysis extent 0.36 10.4 1.51 8.2 0.21 14.1

d 114 8.2 10%2

ph

ph

WW

= − ≈d 14%a

a

CC

= +


Ca in 1982 ~ 340 Ca in 2010 ~ 389

Vegeta1on response to CO2 fer1lisa1on

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How vegeta>on responds to higher Wph will vary with growing condi>ons

d d d10%ph l l

ph l l

W A EW A E

≈ = −

Op>on 1. Response is only through Al: dAl/Al = 10% & dEl/El = 0% Op>on 2. Response is only through El: dAl/Al = 0% & dEl/El = -‐10% Op>on 3. A reasonable expecta>on is for a 5% to 10% drop in El in dry places.

To maintain maximum water use, water-‐stressed vegeta>on will increase leaf cover to counter the drop in El; therefore we expect a 5 – 10% rise in foliage

cover. This is our a priori es,mate of the CO2-‐induced change in foliage cover

Vegeta>on can respond via Al or El or both


Iden1fying the maximum foliage cover edge

•  A dis>nct, linear edge in P-‐F space that represents the maximum cover againable for a given precipita>on

•  At these loca>ons, all other growing condi>ons can be considered op>mum and we assume the limit to growth is water.

•  Therefore any observed rise in the maximum edge should be related to the rise in Wph, and ∴ CO2.

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The ‘maximum foliage edge’


Results •  Observed change in the maximum edge is +11.3%, close to the predicted +10%

•  Observed across all warm, dry regions of the globe

•  Infers the CO2 response is predominantly via El (leaf transpira>on) not Al (leaf assimila>on)

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1982 2010


Conclusions •  The CO2 fer>lisa>on effect is now large enough that it can be quan>fied from satellite

•  Whilst fer>lisa>on is a global phenomenon, these results only relate to warm, dry regions – other responses to elevated CO2 are expected in different environments

•  Fer>lisa>on may have poten>ally significant (but poorly understood) flow-‐on effects including changes in surface albedo, fire fuel loads, carbon storage, water supplies, tree/grass dynamics, erosion rates, na>ve habitat change...

8 | CO2 fer>lisa>on | Donohue Roderick McVicar Farquhar

LAND AND WATER

w www.csiro.au

Randall Donohue t +61 2 6246 5803 e [email protected]


Predicted change in Wph (1982-‐2010)

Predicted change in LAI (1982-‐2010)


Predicted change in gg (1982-‐2010)

Predicted change in Ag (1982-‐2010)

co2drivenincreasesinvegetaon+ cover 2 - land talk 2... ·...

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