Date of Award
Doctor of Philosophy
Plant, Soil and Environmental Sciences
Mark Radosevich, Joe Zhuang
Yuji Arai, Steven Wilhelm
Soil viruses are ubiquitous in the environment and important for their influence on host community composition and function. Viral infection influences host evolution, metabolism, function, diversity, community evenness, and more. As host bacteria play critical roles in agricultural systems, including nutrient cycling and soil aggregate formation, the influence which soil viruses have on their hosts makes them key players in these systems. However, many important questions remain regarding virus abundance and distribution under human imposed and natural conditions in agricultural systems. Understanding how these conditions impact virus abundance, transport, and community structure is critical for a broader understanding of soil microbial functional diversity.
Here, we undertook two main studies aimed at understanding these conditions. First, we conducted a field-based study of virus and bacteria abundance, as well as viral reproductive strategy, under agricultural management practices including no-till, nitrogen fertilization, and cover crop fertilization. We determined that viral abundance and lysogenic fraction were most significantly influenced by sampling date, rather than by the imposed management practices. Additionally, we determined that increased concentrations of nitrogen elevated virus abundance while lowering bacteria abundance and lysogenic fraction, potentially indicating a community wide prophage induction event.
To explore additional factors which might have influenced virus abundance between sampling dates in our field experiment, we conducted our second main study, which was a lab-based column experiment to mimic natural rainfall or irrigation patterns to determine the influence of interrupted flow patterns on the transport and community composition of viruses in agricultural soils. Additionally, we added atmospheric nitrogen deposition levels of ammonium to our columns to determine if trace levels of nitrogen influenced viral transport and community composition. We determined that interrupted hydrologic flow has more influence on viral transport and abundance than the ammonium amendments. Additionally, we made novel discoveries regarding the differential transport of virus families with varying physiochemical (i.e. shape, size, and surface properties) properties.
In total, we filled important knowledge gaps about the abundance, diversity, and transport of native viruses in natural soil systems, which serves as a foundation for future studies in soil viral ecology in these economically important managed systems.
McDearis, Regan, "Native soil virus abundance, composition, and mobility under natural and managed agricultural conditions. " PhD diss., University of Tennessee, 2022.