Browsing by Author "Duston, Stephanie Ann"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Capturing and Characterizing Soluble Organic Matter Dynamics in Soil Formation Processes
    Duston, Stephanie Ann (Virginia Tech, 2020-08-25)
    Dissolved organic matter (DOM) is a highly complex, heterogeneous mix of compounds with diverse functional groups that contribute to several environmental processes such as organo-mineral complexation, nutrient bioavailability, and mineral dissolution. Because of these contributions of DOM to important ecosystem processes, it is often of interest to quantify the flux of DOM moving through different parts of ecosystems. Unfortunately, the complexity and variability of DOM makes quantification and chemical analysis of fluxes challenging. This thesis has two components, the first examines the potential of using four different resins for the purpose of quantifying time-integrated DOM fluxes across two source (e.g. Douglas fir and Yellow poplar) and concentration (30 and 5 mg C/L) leaf-extracts. The second explores how water soluble organic matter (WSOM) changes along spatial gradients of podzolization in a northeast glaciated headwater catchment. Findings from the resin study suggest that quaternary amine Cl- resins with a cross-linked polyacrylamide matrix and gel structure have the best suitability for in-situ sampling of DOM over time. While these resins only captured and allowed for the analysis of ~ 30% of dissolved organic carbon (C) in a series of laboratory studies, it is recognized that only ~50% of natural DOM may be ionized and sorbed electrostatically. Thus, for mass balance approaches, the use of resins would require an adjustment factor to better estimate soluble loads. Though, the observed robustness across source and concentration suggests that resins may be appropriate for indexing DOM fluxes to compare across space, time, or treatments. The second portion of this study examined chemical characteristics of water-soluble organic matter (WSOM) extracted from soils and of DOM sampled from shallow groundwater wells. Quantification of WSOM carbon content and spectroscopic analyses were used to compare samples based on genetic horizon and to compare differences along gradients of lateral and vertical podzolization. Findings show that there were significant trends in WSOM characteristics along podzolization horizon sequences which are indicative of microbial processing along the hillslope. Comparing spatial development of podzols (e.g. lateral versus vertical) found that WSOM in laterally developed E horizons are more microbial in nature when compared to vertically developed E horizons. There were also significant trends between WSOM extractions and groundwater collected from zones of soil development along a hillslope transect, which suggests some homogenization of WSOM as it is processed and transported downslope. This is evidenced by corresponding trends in fluorescence index, freshness index, and protein percent that were indicative of biogeochemical changes due to microbial processing and complexation. Characterizing WSOM can help predict trends in podzolization, and can help identify hotspots of biogeochemical processing.
  • Thumbnail Image
    Relationships among Root Traits, Nitrogen Availability, and Mineral-Associated Organic Carbon
    Duston, Stephanie Ann (Virginia Tech, 2025-02-26)
    Mineral-associated organic carbon (MAOC) is a vital component of soil health and ecosystem productivity, playing a key role in carbon (C) sequestration and nutrient cycling. This dissertation investigates how plant root traits, nitrogen (N) fertilization, and cover cropping influence soil organic carbon (SOC) and MAOC. In the first chapter, a greenhouse experiment with 30 herbaceous plant species found that non-N-fixing plants exhibited stronger positive correlations with MAOC compared to N-fixing species, which were more closely linked to SOC. Root biomass contributed to decreases in MAOC, while specific root length (SRL), and coarse root traits were found to significantly contribute to increases in MAOC, highlighting the importance of plant root architecture in stabilizing C. In the second chapter which focused on relationships among N-fertilization, root traits, and MAOC, moderate N fertilization (56 and 112 kg N/ha) was found to enhance total SOC (∆SOC) and MAOC (∆MAOC) accumulation in the system, while higher N inputs (168 kg/ha) reduced C gains. Notably, the use of stable isotopes allowed for the quantification of fresh C additions, with results that indicate plant-added MAOC (PA-MAOC) was influenced more by plant species and root traits, such as coarse root length and aboveground biomass, rather than N fertilization. In the third chapter, a long-term field study demonstrated the effectiveness of cover cropping in increasing both SOC and MAOC by 43–59% and 27–36%, respectively, compared to conventional and no-till systems without cover crops. Despite triennial additions of N fertilizer over nine years, no significant increases in SOC or MAOC was observed. Additionally, root biomass exhibited positive trends with MAOC. These findings suggest that cover cropping, combined with no till practices, plays a pivotal role in enhancing MAOC by minimizing soil disturbance and promoting root-driven C inputs. This research highlights the importance of integrating plant species selection, root morphological traits, N management, and conservation practices to optimize long-term C storage (i.e., MAOC) and support sustainable soil management. Future studies should continue to include MAOC and particulate organic carbon fractions as these functional C sub pools may respond differently than bulk SOC pool. Including further studies on the interactions between root morphology, environmental factors, and C/N dynamics is necessary to develop more resilient agroecosystems capable of mitigating C losses and improving long-term soil health.