Contrasting responses in leaf nutrient-use strategies of two dominant grass species along a 30-yr temperate steppe grazing exclusion chronosequence

Grazing exclusion practices can be promising restoration techniques where ecosystem degradation follows from rapidly increasing grazing pressure, as widely observed in northern Chinese grasslands. However, the mechanisms of plant-soil interactions responsible for nutrient cycling restoration remain unclear. We examined the functional response of the two most dominant grass species with contrasting nutrient economies to a grazing exclusion chronosequence varying greatly in soil moisture and extractable N and P. The relative biomass of the nutrient acquisitive species Leymus chinensis increased while that of the nutrient conservative Stipa grandis decreased across the chronosequence. Leymus chinensis displayed increasing leaf nutrient concentration and decreasing nutrient resorption with time since grazing exclusion for both N and P. In contrast, S. grandis showed decreasing leaf N and P concentrations and largely stable nutrient resorption. These differences in plasticity, with respect to nutrient stoichiometry and resorption, suggest contrasting abilities of these two dominant species to compete for soil resources and/or differences in their affinity to the changing forms of soil available N and P likely occurring along the restoration gradient. Ecosystem trajectory of change after grazing exclusion appears therefore largely dependent on the nutrient use strategies of co-occurring dominant grassland species.