Measuring the influence of environmental conditions on dissolved organic matter biodegradability and optical properties: a combined field and laboratory study

Abstract

Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and can flux CO2 to the atmosphere when labile fractions are degraded, hence DOM degradation is increasingly studied. Some studies have suggested that fluorescence-derived substrate characteristics are useful metrics for estimating bioavailability (as prerequisite condition for biodegradability), however, recent findings on soil organic matter emphasize the importance of ecosystem scale factors such as physical separation of substrate from soil microbial communities and soil physiochemical cycles driving organic matter stability. I extend this principle to soil derived DOM and hypothesize that such environmental conditions, covariant with season, land use and landscape position, impact the composition of soil DOM and activity and abundance of the microbial community, which together govern DOM biodegradability. As a result, DOM bioavailability may not reliably be predicted using substrate characteristics alone. To test these hypotheses, I assessed aqueous soil extracts for water extractable organic carbon (WEOC) content, biodegradability, microbial biomass and fluorescence spectroscopy on water extractable organic matter (WEOM) across a range of environmental conditions in northern Vermont, USA. My results indicate that changes in environmental conditions affect composition, quantity, and biodegradability of DOM. WEOC concentrations were highest in the fall and lowest in the summer, while no significant differences were found between land covers or landscape position, however, DOM biodegradability was significantly higher in the agricultural (AG) site across seasons. Despite a shift in utilized substrate from less aromatic DOM in summer to more aromatic DOM in winter, biodegradability was similar for all seasons. The only exception were cold temperature incubations where microbial activity was depressed, and processing was halted. These results indicate that bioavailability cannot be reliably predicted based on fluorescence-based metric alone, rather, my core findings illustrate a complex picture of how environmental conditions, landscape characteristics, and substrate composition interact to drive the biodegradability of labile carbon pools in the soil environment. This thesis includes i) a background and comprehensive review of literature to inform the reader of any relevant topics, ii) a paper submitted for publication to Biogeochemistry (Chapter 2), and iii) supplemental information containing figures and tables pertinent to the paper.

Anthropogenic Inputs of Terrestrial Organic Matter Influence Carbon Loading and Methanogenesis in Coastal Baltic Sea Sediments

“…This is due to a combination of its refractory molecular composition, being dominated by lignin, cellulose and cutin (de Leeuw and Largeau, 1993) and physical association to protective minerogenic material prior to deposition (Mayer, 1994;Hedges and Keil, 1995). However, riverine fluxes, molecular composition and biological reactivity of OM terr have been shown to be sensitive to anthropogenic activities such as deforestation, ditching, agriculture and industry (e.g., Lambert et al, 2017;Asmala et al, 2019;Deininger and Frigstad, 2019;Landsman-Gerjoi et al, 2020). Rapid inputs of such "anthropogenic" OM terr.…”

Complex Drivers of Riparian Soil Oxygen Variability Revealed Using Self‐Organizing Maps

“…One transect is situated within the Champlain Valley (CV) physiographic province (hereafter referred to as “CV” site), a primarily agricultural catchment in Sheldon, VT. The other transect is located within a 95% forested catchment with minimal anthropogenic impact that is located within the Northern Green Mountain physiographic province (hereafter referred to as “GM” site), approximately 7 km north of the town of Montgomery, VT (Landsman‐Gerjoi et al., 2020).…”

“…Soils at the GM site are Inceptisols (i.e., Fluvaquentic Dystrudepts and Fluvaquentic Endoaquepts; Soil Survey Staff et al., 2019). Both study sites experience a temperate climate with four distinct seasons, including snow‐dominated winters (22% and 24% of annual precipitation at CV and GM site, respectively), a snow melt period, temperate summers with occasional rains, and a fall season with high litter input (Landsman‐Gerjoi et al., 2020). Differences in elevation result in contrasting meteorological conditions between the two sites (Table 1).…”

Woolly beech aphid infestation reduces soil organic carbon availability and alters phyllosphere and rhizosphere bacterial microbiomes

“…Dissolved OM levels in soil solutions and extracts are sensitive indicators for changes in such dynamics (Zsolnay 2003). For instance, cold-water soil extracts reflect nutrient and energy sources for soil microbes (Jandl and Sollins 1997) and contain other metabolites resulting from belowground plant and microbial processes (Gregorich et al 2003;Landsman-Gerjoi et al 2020). Impacts of aphid infestation on easily available OM and on secondary metabolites likely reflect changes in rhizodeposition and/or an altered microbial processing of available substrate, in particular, in the organic layer as an important part of the total soil OM pool.…”