Abstract: Soil viruses are increasingly recognized as important biotic components influencing microbial community dynamics and soil carbon cycling. However, how altered precipitation affects the accumulation of microbial necromass carbon (MNC), a major contributor to stable soil organic carbon (SOC), remains unclear, particularly with respect to the role of virus–microbe interactions. Using a multi-year precipitation-manipulation experiment in a typical temperate steppe on the Loess Plateau, we integrated viral and microbial sequencing, amino sugar biomarkers, and structural equation modeling to examine how altered precipitation affects MNC accumulation through changes in viral and microbial communities. Altered precipitation significantly affected the diversity and composition of soil viral and microbial communities, with particularly pronounced effects on viral and fungal α diversity. Decreased precipitation significantly reduced bacterial necromass carbon (BNC), total MNC, and their respective contributions to SOC, whereas increased precipitation also reduced MNC, primarily through reductions in BNC, with comparatively weaker effects on fungal necromass carbon. Structural equation modeling further suggested that soil moisture mediated the relationships between altered precipitation, viral and microbial community attributes, and MNC accumulation. In addition, virus–microbe network complexity was positively associated with MNC accumulation and the contribution of MNC to SOC. These findings highlight virus–microbe interactions as a potentially important biotic pathway linking altered precipitation to MNC accumulation and suggest that incorporating virus–microbe associations may improve predictions of soil carbon sequestration in water-limited grasslands.

Key words: Microbial necromass carbon, Network interactions, Precipitation, Semi-arid typical steppe, Soil microbes, Soil viruse