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Biogeosciences Discuss., 9, 4245-4283, 2012
www.biogeosciences-discuss.net/9/4245/2012/ doi:10.5194/bgd-9-4245-2012 © Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License. |
Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance
1Department of Ecology and Evolutionary Biology, Corson Hall, Cornell University, Ithaca, NY 14853, USA
2National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000, USA
Abstract. Plants exchange carbon dioxide and water, two key greenhouse gases, with the atmosphere through the processes of photosynthesis and transpiration, making them essential in climate regulation. Carbon dioxide and water exchange are typically coupled through the control of stomatal conductance, and the parameterization in many models often predict conductance based on photosynthesis values. Some environmental conditions, like exposure to high ozone (O3) concentrations, alter photosynthesis independent of stomatal conductance, so models cannot accurately predict both. The goals of this study were to test direct and indirect photosynthesis and stomatal conductance modifications based on O3 damage in a coupled Farquhar/Ball-Berry model. The same modifications were then tested in the Community Land Model (CLM) to determine the impacts on gross primary productivity (GPP) and transpiration. Modifying the Vcmax parameter and directly modifying stomatal conductance best predicts photosynthesis and stomatal conductance responses to chronic O3 over a range of environmental conditions. On a global scale, directly modifying conductance reduces the effect of O3 on both transpiration and GPP compared to indirectly modifying conductance, particularly in the tropics. The results of this study suggest that independently modifying stomatal conductance can improve the ability of models to predict hydrologic cycling, and therefore improve future climate predictions.
Citation: Lombardozzi, D., Levis, S., Bonan, G., and Sparks, J. P.: Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance, Biogeosciences Discuss., 9, 4245-4283, doi:10.5194/bgd-9-4245-2012, 2012.