Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China. Grazing exclusion (GE) is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services. Nevertheless, there are still significant controversies concerning GE's effects on grassland diversity as well as carbon (C) and nitrogen (N) storage. It remains poorly understood in the arid desert regions, whilst being essential for the sustainable use of grassland resources. To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions, we investigated the community structure and plant biomass, as well as C and N storage of plants and soil (0-100 cm depth) in short-term GE (three years) plots and adjacent long-term freely grazing (FG) plots in the areas of sagebrush desert in Northwest China, which are important both for spring-autumn seasonal pasture and for ecological conservation. Our findings indicated that GE was beneficial to the average height, coverage and aboveground biomass (including stems, leaves and inflorescences, and litter) of desert plant community, to the species richness and importance values of subshrubs and perennial herbs, and to the biomass C and N storage of aboveground parts (P<0.05). However, GE was not beneficial to the importance values of annual herbs, root/shoot ratio and total N concentration in the 0-5 and 5-10 cm soil layers (P<0.05). Additionally, the plant density, belowground biomass, and soil organic C concentration and C storage in the 0-100 cm soil layer could not be significantly changed by short-term GE (three years). The results suggest that, although GE was not beneficial for C sequestration in the sagebrush desert ecosystem, it is an effective strategy for improving productivity, diversity, and C and N storage of plants. As a result, GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.