Short-term grazing exclusions reduced soil organic carbon but not bacterial diversity in the sagebrush desert, Northwest China

Background and aims: In practice, a grazing exclusion (GE) is an effective management method that is used to restore degraded grasslands across the world. However, the effect of GEs on soil organic carbon (SOC) and soil microbial diversity is highly controversial and needs further research across different regions. Methods: We investigated the impacts of short-term GEs (4–7 years) on SOC and soil bacterial diversity in sagebrush desert pastures on the northern slopes of Mt. Tianshan, Northwest China, with a paired experimental design. Five sagebrush desert sites were selected, namely, the Xinyuan plot, Bole plot, Manas plot, Hutubi plot, and Qitai plot. The SOC content was determined by using the Walkley-Black method, and soil bacterial diversity was analyzed by high-throughput gene detection. Results: Compared with freely grazed plots, short-term GEs decreased the SOC content and SOC stock in the 0–10 cm layer. GEs significantly decreased the SOC in the 0–10 cm layer by 14.94% and 53.42% in the Xinyuan and Qitai plots, respectively, and significantly increased the SOC by 14.7% in the 0–5 cm layer of the Bole plot (P < 0.05). The dominant phyla of the soil bacterial community in the sagebrush desert were Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi, and GEs altered their relative abundances. GEs increased the relative abundance of Acidobacteria by 1.18–6.16% and decreased that of Bacteroidetes by 16.25–31.51% (P > 0.05). The relative abundances of Acidobacteria and Firmicutes in the 0–5 cm layer increased by 7.40% and 10.37% in the GE plots, while those in the 5–10 cm layer decreased by 5.08% and 69.62%, respectively (P > 0.05). GEs reduced the Chao1 index, Shannon index and Pielou index of the soil bacterial communities (P > 0.05). GEs reduced the effect of soil bacterial diversity on SOC content. Conclusion: The short-term GEs decreased the SOC content and SOC stock in the 0–10 cm layer in the sagebrush desert, and these values were even significantly reduced at some sites. Nevertheless, the short-term GEs had no significant effect on soil bacterial diversity or dominant bacteria such as Actinobacteria. Our results suggested that short-term GEs exhibited weak negative impacts on soil organic carbon and soil bacterial diversity in the sagebrush desert, and ecological restoration needs to be longer under grazing exclusions.