Exogenous carbon-to-nitrogen imbalance drives soil viral roles in microbial carbon mineralization and necromass accrual

Viruses are integral components of soil microbial community dynamics and carbon cycling, yet their roles in modulating organic matter (OM) transformations under varying nutrient conditions remain poorly understood. This study investigates how exogenous substrate treatment carbon-to-nitrogen (C/N) ratios influence soil viral communities and their roles in microbial activities and necromass carbon accrual in soils differing in physicochemical properties, including native OM contents. A 28-day incubation experiment was conducted using glucose and NH₄Cl amendments at C/N ratios of 5, 10, and 35 in soils from the Songnen and Liaohe Plains. Viromic analyses revealed that both soil properties and amendment C/N ratios significantly shaped viral diversity and composition. Notably, viral species richness and diversity were higher in LH-soils than in SN-soils and were significantly increased upon exogenous substrate addition in both soil types. In SN-soils, viral species richness declined with increasing amendment C/N ratios, coupled with shifts in viral lifestyle balances, underscoring the importance of nitrogen availability in virus-bacterial interactions. The relative abundance of temperate and virulent viruses exhibited distinct patterns associated with multiple soil properties, influencing microbial community interactions and necromass carbon accrual. Structural equation modeling (SEM) indicated divergent effects of viral communities on SOC accumulation across soils. In LH-soils, viral activity negatively associated with bacterial diversity and microbial necromass accumulation (using amino sugar biomarkers as proxies). In contrast, viral dynamics appeared to facilitate necromass incorporation into SOC in SN-soils, suggesting context-dependent viral influences on carbon sequestration. These findings highlight the critical yet nuanced roles of soil viruses in nutrient cycling and carbon storage, providing novel insights into viral ecological functions under varying nutrient and soil context conditions.