Composition of soil viral and bacterial communities after long-term tillage, fertilization, and cover cropping management

Soil bacterial communities are critical for stability and function of terrestrial ecosystems. Viruses are ubiquitous in soils and have significant impacts on the structure and functions of bacterial host communities. However, little is known concerning the impact of various land use management practices on bacterial and viral communities. This study aimed to estimate variations of composition and structure of bacterial and viral communities under long term management practices including inorganic N fertilization, cover cropping, and tillage treatments in a long-term conservation management experimental site in western Tennessee USA. We evaluated bacterial and DNA viral diversity using 16s rRNA sequencing and RAPD-PCR, respectively, and enumerated viral and bacterial abundance via epifluorescence microscopy. Structural equation modeling was applied on the dataset to reveal relationships among viruses, bacteria and soil properties. No significant differences in bacterial alpha-diversity were identified among inorganic N fertilization (ammonia nitrate), cover cropping, and tillage treatments. However, community structure (beta-diversity) differed significantly. Higher soil pH and water content favored greater bacterial abundances. Cover cropping, soil water content, and bacterial abundances were the main factors explaining the variation of viral abundances and community structure in soil. Structural equation modeling suggested that bacterial abundances positively influenced viral abundances, and in turn virus abundances and bacterial alpha diversity affected the level of extractable dissolved organic C, which exerted a feedback effect on the structure of bacterial communities. This feedback loop suggests that bacterial lysates resulting from viral infection might significantly contribute to the reshaping of bacterial community structure while indirectly influencing bacterial alpha diversity. This supports the theory of the ''viral shunt'' in soil ecosystems. This study suggests that the structure of soil bacteria and viruses can be reshaped by long-term management practices. Viruses may indirectly involve in C cycling through positively influencing microbial dissolved organic C under long-term conservation management practices.