Effects of short-term warming and grazing on soil microbial communities in saline-alkaline grasslands of northern China.

Introduction: Soil microbial communities play a central role in material cycling and energy transformation within grassland ecosystems. Alterations in their community structure, diversity, and function directly influence soil ecological functions and ecosystem stability. Global warming exerts persistent environmental pressure on soil microbial communities by modifying soil water and thermal conditions. As a widespread form of human disturbance, grazing interacts with warming to potentially exert complex effects on subterranean microbial processes. Methods: This study investigates the coupled effects of short-term warming and grazing on soil bacterial and fungal communities in saline-alkaline grasslands of northern China. A factorial experiment combining canopy warming (+ 2°C) with four grazing intensities (no grazing, light grazing, moderate grazing, heavy grazing) was conducted, using high-throughput sequencing and multivariate statistical analysis. Results: The research findings indicate that the bacterial community is dominated by Pseudomonadota and Actinomycetota, while the fungal community is primarily composed of Ascomycota and Basidiomycota. The interaction between warming and heavy grazing significantly increased the relative abundance of Pseudomonadota. Warming significantly enhanced the bacterial richness index, whereas fungal α-diversity indices showed an overall declining trend under warming. Grazing tended to increase the topological complexity of bacterial networks, while decreasing that of fungal networks. The impact of warming on network topological structure was relatively limited. Pearson correlation and Redundancy Analysis (RDA) confirmed that dissolved nitrogen (DN) and the ratio of dissolved organic carbon to dissolved nitrogen (DOC/DN) were the main environmental factors driving microbial community variation in this region. Soil microbial communities were primarily associated with nutrient factors, while also being influenced by soil water content. Conclusion: Overall, the effects of grazing on soil bacterial and fungal community structure and α-diversity were relatively minor. Bacterial and fungal α-diversity indices showed differentiated responses to warming, with warming significantly increasing bacterial richness while fungal diversity declined under warming. Available nutrients (DN and DOC/DN) were the primary drivers of microbial community variation. This study extends research on the impact of short-term warming pulses against a background of long-term grazing on soil microbial communities in saline-alkaline grasslands, revealing the critical role of available nutrients in regulating microbial communities in such ecosystems. It provides a scientific reference for the adaptive management of grasslands in ecologically fragile regions of northern China under climate change.