Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Environmental and Soil Sciences

Major Professor

Sean M. Schaeffer

Committee Members

Mark Radosevich, Jennifer M. DeBruyn, Margaret E. Staton


Soil microbial communities are a critical component for ecosystem stability and function. Viruses, as an important biotic controller, have the potential to regulate the abundance and diversity of bacterial communities through infection. Soil is known to harbor abundant and diverse viral assemblages but their ecological role and influence on microbial processes has not been fully elucidated. Microbes can be influenced by viruses not only from infection but though biogeochemical feedbacks of the “microbial (bacterium–phage–DOC) loop” or “viral shunt”. However, we know relatively little about the microbial community and function under the regulation of viruses in soil and how they respond to agricultural management under climate change. The objectives in this dissertation were (1) to estimate variability of soil viral and bacterial communities under a long-term conventional tillage, cover cropping and inorganic N fertilization management practices, and (2) to access the effect of seasonal change on soil bacteria community diversity and structure, and (3) identify the correlation between viruses and their host, and (4) reveal the response of microbial functional genes (C-degradation and N-cycling genes) on cover cropping and fertilization, and the potential roles of viruses on C-degradation. Soil treatments including two nitrogen rates (0, 67 kg N/ha -1), three levels of cover crop (no-cover, hairy vetch and winter wheat), and two tillage managements (conventional tillage and no tillage) from West Tennessee Agriculture Research and Education Center in Jackson were used. The soil bacterial diversity, functional gene and viral diversity was evaluated by 16S rRNA amplicon sequencing, RAPD-PCR, and bulk soil metagenomic sequencing. My findings highlight the importance of microbial on N fertilization and cover cropping in maintaining long-term C pool stability and N concentractions in agricultural soil, and the impact of viruses on C metabolism through regulating microbial metabolism using auxiliary metabolic genes. This study improves our understanding the ecological roles of soil viruses in influencing soil functions under long-term conservation agricultural management.

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