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Partitioning direct and indirect effects reveals the response of water-limited ecosystems to elevated CO2

Partitioning direct and indirect effects reveals the response of water-limited ecosystems to elevated CO2
Partitioning direct and indirect effects reveals the response of water-limited ecosystems to elevated CO2
Increasing concentrations of atmospheric carbon dioxide are expected to affect carbon assimilation and evapotranspiration (ET), ultimately driving changes in plant growth, hydrology and the global carbon balance. Direct leaf biochemical effects have been widely investigated, while indirect effects, although documented, elude explicit quantification in experiments. Here, we used a mechanistic model to investigate the relative contributions of direct (through carbon assimilation) and indirect (via soil moisture savings due to stomatal closure, and changes in leaf area index, LAI) effects of elevated CO2 across a variety of ecosystems. We specifically determined which ecosystems and climatic conditions maximise the indirect effects of elevated CO2. The simulations suggest that the indirect effects of elevated CO2 on net primary productivity are large and variable, ranging from less than 10% to more than 100% of the size of direct effects. For ET, indirect effects were on average 65% of the size of direct effects. Indirect effects tended to be considerably larger in water-limited ecosystems. As a consequence, the total CO2 effect had a significant, inverse relationship with the wetness index and was directly related to vapor pressure deficit. These results have major implications for our understanding of the CO2-response of ecosystems and for global projections of CO2 fertilization because, while direct effects are typically understood and easily reproducible in models, simulations of indirect effects are far more challenging and difficult to constrain. Our findings also provide an explanation for the discrepancies between experiments in the total CO2 effect on net primary productivity.
0027-8424
12757-12762
Fatichi, Simone
2a12468d-8094-495b-922d-4d00aa0afb11
Leuzinger, Sebastian
4ff6805a-918b-41aa-8136-f7391653efbd
Paschalis, Athanasios
e7626e9f-172b-4da2-882c-bddb219f3fb6
Langley, Adam J.
620b1d51-4532-4fb0-bc3d-a4de88e0bc74
Donnellan Barraclough, Alicia
4e03230c-ddeb-47bf-8b0c-ebb281fbc8e6
Hovenden, Mark J.
463ce290-2041-490b-b49a-89ed513d212f
Fatichi, Simone
2a12468d-8094-495b-922d-4d00aa0afb11
Leuzinger, Sebastian
4ff6805a-918b-41aa-8136-f7391653efbd
Paschalis, Athanasios
e7626e9f-172b-4da2-882c-bddb219f3fb6
Langley, Adam J.
620b1d51-4532-4fb0-bc3d-a4de88e0bc74
Donnellan Barraclough, Alicia
4e03230c-ddeb-47bf-8b0c-ebb281fbc8e6
Hovenden, Mark J.
463ce290-2041-490b-b49a-89ed513d212f

Fatichi, Simone, Leuzinger, Sebastian, Paschalis, Athanasios, Langley, Adam J., Donnellan Barraclough, Alicia and Hovenden, Mark J. (2016) Partitioning direct and indirect effects reveals the response of water-limited ecosystems to elevated CO2. Proceedings of the National Academy of Sciences, 113 (45), 12757-12762. (doi:10.1073/pnas.1605036113).

Record type: Article

Abstract

Increasing concentrations of atmospheric carbon dioxide are expected to affect carbon assimilation and evapotranspiration (ET), ultimately driving changes in plant growth, hydrology and the global carbon balance. Direct leaf biochemical effects have been widely investigated, while indirect effects, although documented, elude explicit quantification in experiments. Here, we used a mechanistic model to investigate the relative contributions of direct (through carbon assimilation) and indirect (via soil moisture savings due to stomatal closure, and changes in leaf area index, LAI) effects of elevated CO2 across a variety of ecosystems. We specifically determined which ecosystems and climatic conditions maximise the indirect effects of elevated CO2. The simulations suggest that the indirect effects of elevated CO2 on net primary productivity are large and variable, ranging from less than 10% to more than 100% of the size of direct effects. For ET, indirect effects were on average 65% of the size of direct effects. Indirect effects tended to be considerably larger in water-limited ecosystems. As a consequence, the total CO2 effect had a significant, inverse relationship with the wetness index and was directly related to vapor pressure deficit. These results have major implications for our understanding of the CO2-response of ecosystems and for global projections of CO2 fertilization because, while direct effects are typically understood and easily reproducible in models, simulations of indirect effects are far more challenging and difficult to constrain. Our findings also provide an explanation for the discrepancies between experiments in the total CO2 effect on net primary productivity.

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More information

Accepted/In Press date: 23 September 2016
e-pub ahead of print date: 24 October 2016
Published date: 8 November 2016
Organisations: Water & Environmental Engineering Group

Identifiers

Local EPrints ID: 401962
URI: https://eprints.soton.ac.uk/id/eprint/401962
ISSN: 0027-8424
PURE UUID: c24249a0-b25b-4c62-90fe-2d55d4cf0f41
ORCID for Athanasios Paschalis: ORCID iD orcid.org/0000-0003-4833-9962

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Date deposited: 26 Oct 2016 08:55
Last modified: 02 Dec 2019 19:53

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