Graduate Thesis Or Dissertation
 

Determinants of microbial community structure and substrate utilization potential in soils of vegetable cropping systems

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7d278w33j

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  • The Oregon Long-Term Soil Quality Project was initiated to identify soil properties that respond rapidly to alternative management practices. Such practices included winter cover cropping, which was implemented at two experimental research stations and several grower fields throughout the Willamette Valley. The goal of this thesis was to identify the major impacts of cover cropping on soil microbial community structure, diversity, and substrate utilization potential. Microbial community structure was assessed by extracting fatty acids from soil and analyzing community fatty acid methyl ester (FAME) profiles. Two different methods for extracting fatty acids were tested; these were the ester linked method and the MIDI method developed by Microbial ID, Inc. (Newark, DE). Both methods discriminated among communities from different soils, but the types and relative amounts of fatty acids extracted differed by method. Microbial communities also were characterized by their potential to utilize a diverse range of carbon substrates using the Biolog assay. In a laboratory incubation study, the Biolog assay demonstrated that the types and overall diversity of substrates utilized were affected by the complexity of carbon substrate added to soil. In addition, Biolog diversity was significantly correlated with community FAME richness (r = 0.59). FAME and Biolog assays were applied to field soils of the Soil Quality Project. Changes occurred in microbial FAME structure and Biolog potential in response to winter cover cropping, but effects often were not observed until incorporation of cover crops to soil. In some soils containing cover crop residues, there were greater amounts of eukaryotic FAME markers compared to winter-fallow soils, suggesting greater fungal and protozoan populations in cover-cropped soil. Biolog diversity also was greater in cover-cropped soil compared to fallow soil, which may reflect the utilization of cover crop residues by soil microorganisms during the summer months. Community patterns across different sizes of soil aggregates also were assessed. Biolog diversity was heterogeneously distributed among aggregates, and winter cover cropping elevated FAME diversity across all but the largest (2.0-5.0 mm) aggregate size class. This thesis also identified season and soil type as strong determinants of microbial community structure.
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