The effects of short-term grazing on plant and soil carbon and nitrogen isotope composition in a temperate grassland

Abstract To clarify effects of short-term grazing on C and N contents and dynamics in temperate grasslands, we examined aboveground biomass, vegetation cover, plant and soil C, N, C:N ratio, δ13C, δ15N, Δδ13C and Δδ15N across five grazing intensities. Grazing had no effects on vegetation and soil C, but increased vegetation and soil N. As indicated by grazing increasing △δ13C and reducing soil δ15N, grazing accelerated soil organic carbon (SOC) decomposition but decelerated the rate of N production. Contrasting effects of increased SOC decomposition and allocation of more belowground biomass are suggested to be responsible for SOC not changing. The effects of grazing on plant δ13C differed among species, but for most species grazing increased plant δ13C. However, grazing reduced vegetation δ13C, the opposite trends of species and community levels indicating that grazing would change plant species composition. Reduced Δδ15N indicates that grazing would change the main N sources used by plants. The study emphasizes that measuring plant and soil δ13C, δ15N, △δ13C and △δ15N simultaneously is necessary to comprehensively understand how grazing influences C and N dynamics in plant-soil systems. We also raise the concern that grazing would eventually lead to loss of SOC with consequent decline in C sequestration.