Comparative analysis of stomatal conductance in plants exposed to moderate and high relative humidity

Relative humidity (RH) plays a pivotal role in regulating plant transpiration by modulating stomatal conductance ( g_\texts ). Accurate modeling under varying RH conditions is essential for predicting plant water use and gas exchange, with important implications for both agricultural management and bionic applications. In this study, field experiments were conducted to measure g_\texts in plants exposed to moderate- and high-RH environments. The results demonstrated that g_\texts is greater and transpiration rates are lower in high-RH environments than in moderate-RH environments. The response functions of stomatal conductance to environmental factors were further developed via a boundary line technique. These functions elucidate how stomatal conductance is correlated with environmental conditions. Specifically, stomatal conductance reaches saturation at a photosynthetically active radiation (PAR) of approximately 300 and 500\,\, \mu \textmol/m^2\cdot \texts in both high- and moderate-RH environments. Furthermore, the VPD threshold triggering stomatal closure was shifted by ambient RH, occurring at approximately 1000 Pa under high RH and 2000 Pa under moderate RH. This RH-dependent adjustment highlights the indirect yet critical role of RH in modulating stomatal sensitivity to atmospheric dryness. On the basis of the established response functions, stomatal conductance models tailored for high- and moderate-RH environments were constructed by extending the Jarvis empirical framework. These models offer improved predictive capacity for simulating plant physiological responses under diverse humidity conditions and provide new insights into the stomatal regulation of plants in natural field settings.