Community characteristics and carbon and nitrogen storage in arid and semiarid sagebrush deserts in Xinjiang, China: effects of grazing exclusion

Grazing exclusion (GE) is one of the most common ways to restore degraded grasslands. However, the effects of GE on grassland community characteristics and carbon (C) and nitrogen (N) storage remain unclear, especially in deserts. To further assess the effects of GE on plant and soil properties in arid and semiarid deserts, the community biomass, diversity, and ecosystem C and N contents and storage were determined from GE (6 years) plots and adjacent freely grazed (FG) plots in sagebrush deserts, which are vital spring-autumn pastures in Xinjiang, China. The results revealed that GE had surprisingly dissimilar influences on the plant community and soil properties in both regions. In the semiarid desert, the richness index, diversity index, and evenness index in the GE plot decreased by 41.9, 70.1, and 54.9% compared to those in the FG plot. In the arid desert, the average height, total coverage, and above- and belowground biomass in the GE plot increased by 55.1, 157.1, 207.3, and 322.2% (p < 0.05), respectively, compared to those in the FG plot. However, GE had no significant effect on above- or belowground biomass in the semiarid desert. In addition, in the semiarid region, GE not only decreased the SOC (top 70 cm soil) and STN (top 100 cm soil) concentrations but also significantly decreased the total SOC and STN storage in the top 100 cm of soil by 43.5 and 39.1% (p < 0.05), respectively, and the ecosystem C and N storage in the GE plot decreased significantly, by 39.1 and 36.7%, respectively, compared to that in the FG plot. These findings indicate that GE is an effective approach to improving desert productivity in sagebrush desert ecosystems, especially in arid regions, but may not be beneficial for diversity maintenance or C and N sequestration.