| 摘 要： |
Stomatal conductance (g(s)) of all coexisting species regulates transpiration in arid and semiarid grass-lands prone to droughts. However, the effect of drought stress on canopy conductance (G(s)) is debated, and the interactive effects of abiotic and biotic constraints on G(s) remain poorly understood. Here, we used O-18 enrichment above the source water (Delta O-18) of leaf organic matter as a proxy for G(s) in order to increase the understanding of these effects. Three grassland transects were established along aridity gradients on the Loess Plateau (LP), the Inner Mongolian Plateau (MP), and the Tibetan Plateau (TP), which differ with respect to solar radiation and temperature conditions. Results showed that G(s) consistently decreased with increasing aridity within transects. G(s) on the TP was lower than that on the other two plateaus for a given level of aridity due to low temperature and high radiation. The primary determinant of drought stress on G(s) was soil moisture (SM) on the LP and MP, whereas it was the vapor pressure deficit (VPD) on the TP. Solar radiation exhibited a consistently negative effect on G(s) via drought stress within transects, while temperature had negative effects on G(s) on the TP but no effect on the LP or MR. Adding the interaction of leaf area and abiotic factors increases the percentage of explained variability in G(s) by 17 % and 36 % on the LP and MP, respectively, although this is not the case on the TP, where the climate exerts an overwhelming effect. These results highlight the need to integrate multiple stressors and plant properties to determine spatial variability in G(s). |
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