Opposite responses in leaf N and P concentrations and resorption of two dominant grass species along a 30-yr temperate steppe restoration chronosequence

Background/Question/Methods

Because rapidly increasing grazing pressure is the main factor of ecosystem degradation observed in more than 90% of northern Chinese grasslands, grazing exclusion practices are regarded as promising restoration techniques. However, the role of plant-soil interactions in driving trajectories of changes in nutrient cycles in these restored grasslands is still unclear. Here we hypothesize that positive changes in soil moisture and nutrient availability associated with grazing exclusion would impact differentially on two dominant grass species with contrasting nutrient economics with respect to plant nutrient content and recycling, therefore reinforcing positive plant-soil feedbacks on nutrient cycling.

Results/Conclusions

Whereas soil inorganic N and water availability increased across the restoration chronosequence, soil P availability decreased slightly. Despite these opposite gradient in soil nutrient availability, Leymus chinensis displayed increasing leaf N and P concentrations and decreasing nutrient resorption with time since grazing exclusion. In contrast, Stipa grandis showed decreasing leaf N and P concentrations and largely stable nutrient resorption. This decoupling between soil inorganic nutrients and plant nutrient status suggests contrasting abilities of Leymus chinensis and Stipa grandis 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. Our results suggest that species-specific interactions between plants and soil play a major role for nutrient cycling during grassland restoration.