Phosphorus Availability Mediates Grazing Impacts on Resorption and Allocation of Foliar Nitrogen and Phosphorus by Dominant Species in Semiarid Grasslands

Nutrient resorption and relative allocation of nutrient to younger leaves are important mechanisms of resource conservation and utilization for perennial plants. However, it remains unclear how grazing and soil nutrient levels, particularly phosphorus (P) availability, affect nutrient resorption and allocation by perennial species. We investigated the impacts of long-term grazing (i.e., the legacy effect of grazing intensity) and soil P fertilization on nitrogen (N) and P resorption and allocation by two dominant perennial species, Stipa grandis and Carex korshinskyi, in a semiarid grassland. Foliar N and P concentrations of both species increased with grazing intensity under both low and high P availability, except P concentrations under high P conditions. For S. grandis, N and P resorption efficiencies (NRE, PRE) increased with grazing intensity under low P conditions, but PRE decreased with increasing grazing intensity under high P conditions. For C. korshinskyi, grazing decreased NRE under low P conditions but increased NRE under high P conditions. Relative P allocation to younger leaves by the two species increased with grazing intensity under low and high P conditions. For both species, the relationship between nutrient resorption and allocation shifted from synergistic under low P conditions to neutral or trade-off relationships under high P conditions. Our findings demonstrate that grazing has strong effects on foliar N and P concentrations and resorption and allocation, but these effects depend on soil P availability and species identity. High levels of grazing intensity exacerbate P limitation and alter N and P resorption and allocation in both dominant species, except P resorption of Carex korshinskyi. This study provides important insights into the mechanisms underlying grazing impacts on ecosystem N and P cycling.