Influence of aridity and salinity on plant nutrients scales up from species to community level in a desert ecosystem

Soil moisture and salt play key roles in regulating desert plant nutrient cycles on a local scale. However, information on the response of plant nutrient stoichiometric patterns to soil water and salt gradients is limited. Here, we assessed leaf N and P levels of 18 species of desert plants and measured the corresponding soil nutrient, water and salt concentrations, at four dry sites, five humid-saline sites and four humid-non-saline sites (reference sites) along a transect in a temperate desert in Xinjiang Province, northwest China. Our results indicated that the desert plants had lower N and P concentrations and higher N:P mass ratios in dry and humid-saline sites than in the humid-non-saline sites. Unlike the single-factor effect of salinity driving the plasticity of species N concentration, aridity and salinity interacted in their impact on the plasticity of plant P and the N:P ratio. Moreover, the plant community N and P concentrations and N:P ratio exhibited significant positive linear and nonlinear correlations with soil moisture in shallow and deep soil, respectively. Aridity reduced the N plasticity and increased P plasticity of the plant community. The results strongly supported the hypothesis that soil moisture and salt concentration were the dominant drivers of leaf N and P concentrations and their plasticity across species and community scales.