Data_Sheet_2_A Whole Leaf Comparative Study of Stomatal Conductance Models.PDF

We employed a detailed whole leaf hydraulic model to study the local operation of three stomatal conductance models distributed on the scale of a whole leaf. We quantified the behavior of these models by examining the leaf-area distributions of photosynthesis, transpiration, stomatal conductance, and guard cell turgor pressure. We gauged the models' local responses to changes in environmental conditions of carbon dioxide concentration, relative humidity, and light irradiance. We found that a stomatal conductance model that includes mechanical processes dependent on local variables predicts a spatial variation of physiological activity across the leaf: the leaf functions of photosynthesis and transpiration are not uniformly operative even when external conditions are uniform. The gradient pattern of hydraulic pressure which is needed to produce transpiration from the whole leaf is derived from the gradient patterns of turgor pressures of guard cells and epidermal cells and consequently leads to nonuniform spatial distribution patterns of transpiration and photosynthesis via the mechanical stomatal model. Our simulation experiments, comparing the predictions of two versions of a mechanical stomatal conductance model, suggest that leaves exhibit a more complex spatial distribution pattern of both photosynthesis and transpiration rate and more complex dependencies on environmental conditions when a non-linear relationship between the stomatal aperture and guard cell and epidermal cell turgor pressures is implemented. Our model studies offer a deeper understanding of the mechanism of stomatal conductance and point to possible future experimental measurements seeking to quantify the spatial distributions of several physiological activities taking place over a whole leaf.

本研究采用精细的全叶水力模型，针对分布于整片叶片尺度下的三类气孔导度（stomatal conductance）模型的局部运行机制展开探究。本研究通过分析光合速率、蒸腾速率、气孔导度以及保卫细胞膨压（guard cell turgor pressure）的叶面积分布特征，量化了这三类模型的运行特性，同时评估了模型对二氧化碳浓度、相对湿度及光照辐照度等环境条件变化的局部响应规律。研究发现，一类纳入依赖局部变量的机械过程的气孔导度模型，可预测叶片内生理活动的空间异质性：即便外部环境条件均一，叶片的光合与蒸腾功能也并非均匀发挥作用。为驱动整片叶片产生蒸腾作用所需的水力压力梯度，由保卫细胞与表皮细胞（epidermal cell）的膨压梯度衍生而来，并通过机械气孔模型进一步导致蒸腾与光合过程呈现非均匀的空间分布格局。本研究通过对比两类机械气孔导度模型版本的预测结果开展模拟实验，结果表明，当气孔开度与保卫细胞、表皮细胞膨压之间呈现非线性关系时，叶片的光合与蒸腾速率空间分布模式以及对环境条件的响应规律均更为复杂。本模型研究深化了对气孔导度调控机制的理解，并为未来通过实验量化整片叶片上多种生理活动的空间分布提供了可行的研究方向。