A stomatal optimization model adopting a conservative strategy in response to soil moisture stress

Leaf stomata play a central role in mediating the exchange of water vapor and carbon dioxide between the atmosphere and the terrestrial ecosystems. Stomatal response to the environment presumably optimizes the trade-off between carbon uptake and water loss. Recently developed optimization models show their remarkable success in capturing empirical patterns of stomata. However, solutions of these models with different mathematical details should vary for the same environments, indicating that stomatal strategies implied in these models may differ and require further investigation. The present study proposed a novel stomatal optimization model, assuming that stomatal regulation aims to achieve a water-carbon balance shaped by a hydraulic-based weight factor (HBW model). In particular, we introduce the balancing point (BP) for analyzing the behavioral difference between models. We tested the HBW model based on set scenarios and leaf-level gas exchange data and compared it with two existing models. Results show that these models differ mainly in stomatal sensitivity to soil moisture. BP characteristics reveal the behavioral difference between models, and only the HBW model, which is more sensitive to soil moisture, captures the actual response patterns of BP to water stress well. This work emphasizes the differences in stomatal strategies among different optimization models, and provides an alternative modeling approach, which offers a more conservative stomatal strategy that can stand as a useful comparison with existing models.