High soil bacterial diversity increases the stability of the community under grazing and nitrogen

Abstract

Grasslands are one of the major terrestrial ecosystems facing severe degradation due to climatic changes and anthropogenic activities. In northwest China, the Typical steppe and alpine meadows are the major grasslands with diverse ecosystems. These grasslands are facing degradation due to excessive livestock grazing and nitrogen (N) deposition that can alter the overall grassland ecosystem, along with the soil bacterial communities and their role in the ecosystem. The bacterial community is vital for the sustainability of grassland ecosystems as it plays a crucial role in decomposing the dead organic matter and nutrient cycling. This study conducted a grazing and N addition experiment in alpine meadows and typical steppe. The impact of short-term N application and grazing on both grasslands' soil, plant, and bacterial communities was explored. Alpine meadows had higher bacterial richness (OTUs>2000) and diversity (Shannon index>6) than the typical steppe (OTUs<900; Shannon index<5.5) due to changes in climate and ecosystem. The alpha diversity (Shannon index) of the bacterial community was observed to increase under low grazing without N addition while adding medium N (100 kg/ha) without grazing increased the diversity. The combination of medium N (100 kg/ha) addition and low grazing resulted in the highest bacterial diversity in both grasslands. In contrast, the combination of N and high grazing decreased bacterial richness and diversity. The N addition and grazing affected the bacterial community composition in the typical steppe. The co-occurrence networks revealed that the network complexity in bacterial communities of alpine meadows was higher than that of typical steppe. The rich bacterial community and high soil nutrients in alpine meadows might have led to diverse microbial functionality, which provided stability to the bacterial network. The low nutrients and water availability in typical steppe lead to a lower bacterial richness, making the bacterial community vulnerable to the changes due to grazing and N. Climate is a significant factor in shaping the grassland ecosystem and its bacterial community. The changes in the grassland’s ecosystem due to high grazing and N deposition would highly affect the distressed microbial communities in arid and semiarid regions. Further, in-depth studies are required to understand the fate of these vulnerable grasslands and design management strategies for their protection.