College of Agriculture & Natural Resources
Permanent URI for this communityhttp://hdl.handle.net/1903/1598
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
Browse
3 results
Search Results
Item Soil microbial processes and community structure in natural and restored tidal freshwater wetlands of the Chesapeake Bay, Maryland, USA(2017) Maietta, Christine E.; Yarwood, Stephane A.; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are integral to downstream water quality because they capture, store, and transform nutrients. Unfortunately, anthropogenic stressors are negatively impacting these habitats. While wetland restoration is helping to reinstate their presence in the landscape, restored wetlands frequently differ physically, chemically, and biologically from their natural counterparts. This research examined plant, soil, and microbe relationships and how their interactions affect soil carbon (C) storage and cycling in natural and restored tidal freshwater wetlands of the Chesapeake Bay, MD, USA. This research yielded important findings regarding differences between natural and restored habitats. First, we discovered soil microbial community composition of an urban tidal freshwater wetland retained similar composition as their less disturbed, suburban counterpart, and wetland sites constructed using similar restoration methodology produced similar microbial community structure and soil function. Additional research revealed that a natural and a restored wetland store soil C quite differently: A majority of soil C in the natural site was associated with large macroaggregates (> 2000 μm) whereas most soil C in the restored site was associated with smaller macroaggregates (> 250 to < 2000 μm). The distributions of six chemical compound classes (i.e., carboxylics, cyclics, aliphatics, lignin derivatives, carbohydrates derivatives, N-containing compounds) were relatively similar across the five soil fractions from both sites, however. In the final study, anaerobic laboratory mesocosms were used to evaluate the effects of clay content (%) and leaf litter quality on soil C cycling processes over time. This study found restored soils, regardless of clay content, mineralized more C as carbon dioxide (CO2) and methane (CH4) compared to natural wetland soils. Natural soils respired approximately half the volume of gas as restored soils, suggesting the addition of high- or low-quality C substrates to low C systems elicit a greater response from the heterotrophic microbial community. The results of these three studies suggest site history and edaphic features of restored wetlands are important drivers of microbial communities and their function. We propose that practitioners and researchers work together to identify practices that will enhance soil functions, particularly C storage, in tidal freshwater wetlands of the Chesapeake Bay region.Item Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation(2016) Allard, Sarah Michelle; Micallef, Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.Item Back to Earth: Molecular Approaches to Microbial Ecology Must Consider Soil Morphology and Physicochemical Properties(2015) Dlott, Glade; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This project studied the influence of different long-term agricultural management regimes on soil microbial communities, and compared survival strategies of individual prokaryotic OTUs in diverse soils subjected to long-term incubation. Together these would show whether alterations to microbial communities affect rates of soil carbon cycling. Agricultural soils were sampled at arbitrary depths above and below the plow layer, and relative abundances of microbes were measured using high-throughput sequencing. `Activity' (rRNA:rDNA) ratios were calculated for individual OTUs identified by high-throughput sequencing of tropical rainforest and temperate cornfield soils after incubation for one year with differing water and carbon availabilities. It was found that depth controls microbial communities to a greater degree than agricultural management, and that the characterization of microbial trophic strategies might be complicated by the often-ignored DNA preservation potential of soil. The study highlights the need for holistic approaches to testing hypotheses in modern microbial ecology.