A unified theory of optimal stomatal behaviors under Rubisco and RuBP-regeneration limitations

Xianhui Tang, Chao Yue, Xin Song, Han Wang, Zhenhong Hu, Qiang Yu, Liguo Zhou, Julien Lamour, Alistair Rogers
The Research Center of Soil and Water Conservation and Ecological Environment, Chinese Academy of Sciences and Ministry of Education, Yangling, Shaanxi 712100, China

Analytical solutions of optimized stomatal behavior predict an invariant scaling between stomatal conductance (gsw) and plant photosynthesis (A), formulating a linear gsw-A relationship with a constant slope parameter (known as stomatal sensitivity, g1). However, observed stomatal responses to environmental changes show a nonlinear relationship without a theoretical justification. We explored the hypothesis that the transition between the photosynthetic states of Rubisco and RuBP-regeneration limitations may account for the observed nonlinearity. To investigate this, we analytically solved both optimization schemes: the maximized water use efficiency hypothesis and the least cost hypothesis, for two photosynthetic limitation states. Both solutions of the two optimization schemes predict that the g1 of the Rubisco-limited state was about two to three times that of the RuBP-regeneration limited state, implying a more sensitive stomatal response to photosynthesis under Rubisco limitation compared to RuBP-regeneration limitation: a prediction which was validated using observations of steady-state gsw response to varied light levels. This work provides a unified theory to resolve ongoing debate surrounding optimal stomatal behavior under the two photosynthetic limitation states and the observed but unexplained nonlinear stomatal response. It hence contributes to improving modeling ecosystem carbon and water fluxes.