Response to reviewer#3

Abstract

Stomatal conductance (gs) of all co-existing species regulates transpiration in arid and semi-arid grasslands prone to droughts. However, the effect of drought stress on gs is debated, and the interaction effects of abiotic and biotic constraints on canopy gs remain poorly understood. Here, we used Abstract. Stomatal conductance (gs) of all co-existing species regulates transpiration in arid and semi-arid grasslands prone 18O enrichment of leaf organic matter above source water (△18O) as proxy for gs per leaf area to increase understanding of these effects. Three grassland transects were established along aridity gradients in Loess Plateau (LP), Inner Mongolian Plateau (MP), and Tibetan Plateau (TP) which differ in radiation and temperature conditions. Results showed that canopy gs consistently decreased with increasing aridity within transects. The order of gs at a given aridity index was LP>MP>TP, due to suppressed effects of excess radiation and low temperatures among transects. Primary determinant of drought stress on gs was soil moisture (SM) in LP and MP, and vapor pressure deficit (VPD) in TP. Radiation exhibited consistently negative effect on gs via drought stress within transects, while temperature had positive effects on gs in LP, no effects in MP, and negative effects in TP. Adding the interaction of leaf area and abiotic factors increases the percent of explained variability in gs by 17 and 36 % in LP and MP, respectively, but not in TP due to an overwhelming effect of climate. The results highlighted the need to integrate multiple stressors and plant properties to determine spatial variability in gs.