Dung-Induced Soil Microbial Community Coalescence Driven by Different Dung Sources: Impacts on Community Shifts and Assembly Mechanisms in Grassland Soils

The overall influences of grazing practice on soil microbial community shifts have received considerable attention, but how dung-induced community coalescence affects soil microbial diversity, structure, interaction and the underlying assembly mechanism remains unclear. To address this, we investigated soil microbial community alterations in response to dung deposition, which included three different dung sources in a single grassland. The results indicated that dung deposition by different livestock species had varying impacts on soil microbial community diversity and structure, with cattle dung associated with the largest observed shifts in soil microbial diversity and community structure in this study. The structure of the soil microbial community was strongly associated with multiple edaphic properties (e.g., pH and nutrient content), but these correlations were reshaped by dung deposition in a dung-source-dependent manner. In addition, dung deposition consistently reduced the complexity and robustness of the co-occurrence network across different dung sources, and the strongest alterations in the network were found in shallow soils (0–20 cm). Null model analysis suggests that dung deposition improved the proportional contribution of the stochastic process in bacterial and fungal communities and conversely increased the deterministic process in the archaeal community, implying distinct assembly mechanisms of those microbial domains to the disturbance induced by dung deposition. These results highlight the source effect of dung deposition on the diversity and structure of soil microbial communities, as well as the domain-dependence of dung deposition on the assembly mechanism. The findings suggest that multispecies grazing is associated with distinct dung-induced microbial community shifts, highlighting the need for future research that explicitly incorporates dung source as a variable in grassland soil microbial assessments.