Viral abundance and lysogenic fraction respond dynamically to cover-crop burn down and vary with conservation soil management practices

Viruses are ubiquitous and abundant in soil and play crucial roles in shaping the diversity and activity of microbial host communities. Viral lytic activity yields intracellular matter to the dissolved pool and produces macromolecular microbial necromass, which may be a critical pathway for carbon sequestration. For a complete understanding of the role viruses play in soil food webs, it is important to identify environmental factors that influence virus population dynamics and lytic reproduction in soil. In this study, we examined viral and bacterial abundance using epifluorescence microscopy, and calculated the lysogenic fraction in soils collected from a long-term experimental cotton production system under 12 different conservation management practices in Jackson, Tennessee. The results showed that cover cropping and no-till treatments significantly impacted soil physicochemical factors and increased dissolved organic carbon (DOC) and nitrogen contents. These variations in DOC and nitrogen status in turn had significant correlations with viral and bacterial abundance. However, the variation in viral abundance pre- and post-planting was greater than between imposed conservation management practices. Mean viral abundance across all treatments was highest after planting and following burn-down of winter cover crops (i.e., June 2019), which also had greater mean inorganic nitrogen concentration than the pre-planting samples. Conversely, bacterial abundance and lysogenic fraction were lower post-planting. Overall, this research suggests that viral abundance in field plots maybe affected more by the intra-annual cotton production cycle than by long term management practices. More intensive sampling for a greater duration, capturing seasonal variations, will be necessary to fully reveal the virus-host population dynamics under conservation management practices.