Mixed Grazing Enhances Bacterial Diversity and Network Stability More Than Single Grazing in Both Nondegraded and Moderately Degraded Grasslands

Soil microbial communities are integral in supporting the sustainability of grassland ecosystems. Livestock grazing exerts varied impacts on soil microbial communities due to distinct grazing behaviors and feeding preferences. However, the effects of livestock diversification on the soil microbial community in moderately degraded grassland compared with nondegraded grassland are still uncertain. To narrow this gap, we carried out a grazing experiment in the eastern Eurasian steppe by altering livestock diversification (nongrazing [NG], cattle grazing alone [CG], sheep grazing alone [SG], and mixed cattle and sheep grazing [MG]) in both nondegraded [ND] and moderately degraded grasslands [MD] for 3 years. We applied high-throughput sequencing to investigate microbial diversity, community composition, co-occurrence network structure, and community assembly processes in the topsoil (0–10 cm). Our study revealed that MG significantly enhanced bacterial richness (144.6%, p = 0.005), fungal richness (30%, p = 0.003), network stability and topological properties (5.7% more nodes, and 7.1% higher positive connection ratios) compared to NG in nondegraded grassland. Furthermore, MG had relatively high stability of bacterial networks compared with single grazing in both nondegraded and moderately degraded grasslands. Additionally, the assembly of soil microbial communities in grassland was dominated by stochastic processes, whereas MG reduced the randomness in fungal community assembly. Moreover, bacterial communities exhibited a stronger association with soil characteristics in terms of diversity, composition, and stochastic processes, while fungal communities demonstrated a greater correlation with plant characteristics. Our findings indicated that MG promoted soil bacterial diversity and network stability while reducing the importance of stochastic processes compared to single grazing. However, the effect was largely dependent on the habitat condition of grassland. The results of this study highlight that diversifying livestock grazing can be an effective management practice to maintain the stability of grassland on the eastern edge of the Eurasian steppe belt from the perspective of the soil microbial community.