Doctoral Dissertations
Date of Award
8-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Plant, Soil and Environmental Sciences
Major Professor
Sindhu Jagadamma
Committee Members
Debasish Saha, Melissa Cregger, Jennifer M DeBruyn
Abstract
Soil is vital for agriculture, playing a crucial role in biogeochemical cycles by acting as the largest terrestrial carbon (C) pool, significantly impacting the global C cycle. Intensive agricultural practices have caused an extensive soil organic C (SOC) deficit. Conservation practices like no-tillage (NT) and winter cover cropping help mitigate these deficits by improving soil conditions and supporting active microbial traits associated with C cycling. This aids the crop residue conversion into microbial biomass and by-products, stabilizing them as a more persistent mineral-associated organic matter-C (MAOM-C) pool. Agricultural subsoils beneath the plow horizon, are emerging as potential C sinks due to their unique soil environment, lower management impacts, and a higher abundance of C-unsaturated mineral fraction, presenting an opportunity for secure SOC storage. This research aims to understand microbial functional trait-mediated SOC dynamics under conventional and conservation agricultural practices in both topsoil and subsoil. Utilizing a long-term continuous cotton field experiment in West Tennessee, the study examines the effects of soil depth and agricultural practices on microbial functional traits associated with C cycling and SOC accrual. We hypothesized that conservation practices, particularly NT combined with deep-rooted winter wheat (WW), would enhance microbial functional traits such as carbon use efficiency (CUE) and enzymatic efficiency (EE), leading to increased SOC storage. We found that NT increased topsoil SOC stock than conventional tillage. However, WW increased subsoil SOC stock. A short-term incubation experiment with 13C-glucose addition revealed significant increases in CUE and EE under NT topsoil. WW improved microbial CUE in both topsoil and subsoil layers. A long-term incubation study with 13C-labeled plant residue revealed increased residue-derived C allocation to SOC fraction under long-term cover crops. This increase in SOC was mediated by improved microbial functional traits, increased residue-derived C storage in the MAOM-C pool, and decreased C loss from native SOC. This research demonstrates how management practices and soil depth influence microbial functional traits, affecting SOC dynamics. Strategic implementation of long-term conservation agriculture promotes SOC storage and mitigates C loss, especially in the subsoil. Our results demonstrate the need for further research and policy support to implement agricultural subsoil-targeted SOC sequestration strategies.
Recommended Citation
Patra, Rounak, "Deciphering the Role of Microbial Functional Traits in Agricultural Subsoil Organic Carbon Dynamics. " PhD diss., University of Tennessee, 2024.
https://trace.tennessee.edu/utk_graddiss/10413