Stomatal conductance, closely related to water flow in the soil-plant-atmosphere continuum, is an important parameter in the Penman-Monteith (P-M) model for estimating evapotranspiration (ET). In this study, a novel soil water stress index ω, considering intrinsic soil-plant water relations, was introduced into the Jarvis empirical estimation model of stomatal conductance to improve the representation of the effect of soil water stress on stomatal conductance. The index ω accounted not only for current water availability by combing the effects of relative distribution of soil water to roots and nonlinear stomatal response, but also for the hysteresis effect of water stress by means of the inclusion of a recovery coefficient. Combined plant and soil-based measurements from a greenhouse experiment provided the basis for investigating the relationship between leaf stomatal conductance g_s and root zone soil water stress represented by ω. The response of g_s to root-weighted soil matric potential was found to be nonlinear. The relationship between g_s and the extent of previous water stress (i.e. the water stress recovery coefficient curve) was generalized by a power function and was verified and confirmed using results obtained from the literature. The reliability of ω was tested by coupling it into the Jarvis model to estimate leaf (g_s) and canopy (g_c) stomatal conductance, and thereupon into the P-M model to estimate cumulative ET (CET) in the greenhouse experiment and two field experiments. The estimated g_s, g_c and CET agreed well with the measurements, with root mean squared error not more than 0.0006 m s⁻¹, 0.0020 m s⁻¹ and 8.2 mm, respectively, and determination coefficient (Nash-Sutcliffe efficiency coefficient) consistently greater than 65% (0.14). Therefore, ω should be feasible and reliable to delineate the response of stomatal physiological reaction to water stress, and hence helpful for accurate estimation of ET using Jarvis-based P-M models.

气孔导度与土壤－植物－大气连续体中的水流密切相关，是Penman-Monteith（PM）模型中估算蒸散量（ET）的重要参数。在这项研究中，考虑到内在的土壤-植物水分关系，将一种新颖的土壤水分胁迫指数ω引入到Jarvis气孔电导率的经验估计模型中，以改善土壤水分胁迫对气孔电导率的影响。指数ω通过结合土壤水相对于根的相对分布和非线性气孔响应，不仅解释了当前的水有效性，而且还通过包含恢复系数来解释了水分胁迫的滞后效应。温室试验中基于植物和土壤的联合测量为研究叶片气孔电导g _s与以ω表示的根区土壤水分胁迫之间的关系提供了基础。发现g _s对根系加权土壤基质势的响应是非线性的。g _s之间的关系先前的水压力程度（即水压力恢复系数曲线）通过幂函数进行了概括，并使用从文献中获得的结果进行了验证和确认。通过将其耦合到Jarvis模型中以估计叶片（g _s）和冠层（g _c）气孔导度来测试ω的可靠性，然后将其耦合到PM模型中以评估温室实验和两个田间实验中的累积ET（CET）。 。估计摹_小号，G _Ç和CET与实测值吻合较好，与均方根误差不超过0.0006毫秒^-1，0.0020毫秒^-1分别为8.2毫米和8.2毫米，测定系数（纳什-萨特克利夫效率系数）始终大于65％（0.14）。因此，ω描绘气孔生理反应对水分胁迫的响应应该是可行和可靠的，从而有助于使用基于Jarvis的PM模型准确估算ET。