Comparison of leaf stomatal conductance models for typical desert riparian phreatophytes in northwestern China

Stomatal regulation plays a vital role related to plant functioning, especially with a limited water supply. Estimating the leaf stomatal conductance (g _s) is pivotal for further estimation of transpiration as well as energy and mass balances between air and plant in arid regions. Based on successive measurements of leaf gas exchange of two typical desert riparian phreatophytes, Tamarix ramosissima Ledeb., and Populus euphratica Oliv., we estimated g _s using the empirical, optimal, and mechanistic models. Measurements were conducted on T. ramosissima during the growing seasons in 2011 and 2012 and P. euphratica in 2013 and 2014. Estimated values were compared with those measured by the portable open-path gas exchange measurement system. Results indicated that Ye’s mechanistic model always performed best among all the g _s models tested here with R ² values of 0.878 and 0.723 for T. ramosissima in 2011 and 2012, and 0.625 and 0.867 for P. euphratica in 2013 and 2014, respectively. Meanwhile, Medlyn’s optimal model exhibited the least reliable performance with R ² at values of 0.514 and 0.398 for T. ramosissima in 2011 and 2012, and 0.385 and 0.101 for P. euphratica in 2013 and 2014, respectively. Empirical models may not be suitable for application in novel situations because they have been developed from experimental observations rather than from any mechanistic understanding or theory of stomatal behavior. Consequently, the application of Ye’s mechanistic model will be of great significance for the modeling and up-scaling of g _s in extremely arid regions in the future.