Grazing exclusion effects on above- and below-ground C and N pools of typical grassland on the Loess Plateau (China)

Fencing with grazing exclusion is an effective grassland restoration and management practice used to achieve sustainability of grassland ecosystems worldwide. However, how the fencing with grazing exclusion affects ecosystem services related to carbon and nitrogen dynamics in grassland ecosystems has remained controversial over the past two decades. We investigated plant biomass, diversity and function groups, as well as soil bulk density, pH, soil carbon and nitrogen contents and the carbon/nitrogen ratio within the upper 0–1 m soil layer in fenced grassland with grazing exclusion and in grazed grassland on the Loess Plateau (China) in 2012 and 2013. We estimated the carbon and nitrogen pools of the plants and soils to determine how the grazing exclusion affected them. Results showed that soil carbon content in the topsoil, plant biomass and diversity, and grasses increased, while bulk density, pH and forbs decreased after grazing exclusion. The increases in soil carbon content, the cumulative organic carbon pool and the rate of change in the cumulative organic carbon pool mainly occurred in the upper 20 cm soil layer after 8 years of grazing exclusion. Our study suggested that the 8-year grazing exclusion had a great influence on the carbon pools, but there were no changes in the soil nitrogen pool. Identifying the main factors that affect the carbon and nitrogen dynamics after grazing exclusion among the soil and plant properties should be given more attention in future studies.