Linking Leaf N:P Stoichiometry to Species Richness and Composition along a Slope Aspect Gradient in the Eastern Tibetan Meadows

Abstract

As an important topographical factor, slope aspect has an essential influence on plant community structure and leaf traits. Leaf nitrogen (N) and phosphorus (P) stoichiometry is an important leaf trait indicating plant growth. However, it has rarely been studied how leaf N:P stoichiometry correlates with plant community structure along the slope aspect gradient. To understand the variation of leaf N:P stoichiometry and community structure, as well as their correlation with each other, the species composition and leaf N and P in Tibetan meadows were investigated across three slope aspects: the south-, west-, and north-facing slope aspects (i.e., SFS, WFS, and NFS). In our results, leaf N:P ratio was significantly lower on the NFS than on the SFS, indicating N and P limitation on the NFS and SFS, respectively. Richness of forb species and all species was higher on the NFS than on the SFS and was negatively correlated with leaf N concentration, whereas graminoid richness was not statistically different among the slope aspects and showed a negative correlation with leaf P concentration. Thus, our results provide evidence for the functional significance of leaf N:P stoichiometry for species composition along a natural environmental gradient. Our findings could provide applicable guidance in the refinement of grassland management and biodiversity conservation based on topography.