Improving stomatal optimization models for accurate prediction of photosynthesis under drought conditions.

Accurate estimation of stomatal regulation is crucial for understanding how plants respond to changing environmental conditions, particularly under climate change. While stomatal optimization models have made significant progress in predicting instantaneous plants' carbon and water exchange, they often do not account for biochemical acclimation to drought over long time scales. In this study, we investigated the impact of incorporating photosynthetic acclimation on the accuracy of six stomatal optimization models in predicting carbon and water exchange in terrestrial C3 plants. By introducing the cost of maintaining a certain level of photosynthetic capacity into the stomatal optimization process, we incorporated photosynthetic acclimation to the previous seven days of environmental conditions. Using experimental data from 37 plant species, we found that accounting for photosynthetic acclimation improved the prediction of carbon assimilation in most of the tested models. Additionally, we found that non-stomatal mechanisms significantly contributed to photosynthesis limitation under drought conditions compared to well-watered conditions in all tested models. The hydraulic impairment functions of the stomatal models were unable to accurately account for drought effects on photosynthesis, indicating the need to consider photosynthetic acclimation to improve estimates of carbon assimilation under drought conditions.