Soil viruses reduce greenhouse gas emissions and promote microbial necromass accrual

Viral-induced microbial mortality has been proposed as a major contributor in shaping microbial community structure and function, soil carbon (C) accrual and mobilization of plant available nutrients. Yet, how soil viruses influence soil organic C (SOC) turnover and sequestration remains unknown. Here, we performed microcosm experiments with two distinct soils from grassland (GL) and agricultural (AG) sites and interrogated the roles of soil viruses in driving microbial community succession, SOC transformation and sequestration. The results show that soil viruses affected microbial C use efficiency and reduced respiration in microbial communities obtained from both GL and AG soils. Soil viruses affected microbial successional trajectories (via predation of dominant populations) and functional gene profiles triggering a significant decrease in CO2 and N2O emissions. The impact of soil viruses on microbial community composition in GL microcosms was much less pronounced compared with that in AG microcosms, suggesting contrasting virus-host interaction patterns under different environmental settings. Viral infection significantly enhanced microbial necromass accumulation thereby increasing SOC and total nitrogen (TN) content. The results implicate viral-mediated microbial mortality as a key factor influencing the distribution of C between mineralization and soil C storage pathways. We proposed "viral loop" to explain the crucial function of soil viruses in SOC turnover and sequestration.