Gottshall, C. B. 2015. Effects of different agricultural management systems on arbuscular mycorrhizal fungal diversity, community structure, and ecosystem services. Dissertation, University of Louisville, Louisville, Kentucky, USA.

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Disturbances associated with row-crop agricultural management systems include mechanical (tillage and cultivation) and chemical (fertilizer, pesticides, herbicides, fungicides) inputs and are often co-occurring. Many soil microbes are sensitive to these disturbances, including arbuscular mycorrhizal fungi (AMF), important plant mutualists in agricultural systems. AMF associate with many crop plants and provide direct benefits through root pathogen protection, drought resistance, nutrient acquisition and uptake, as well as contribute to ecosystem services by improving overall soil fertility. Examining how different row-crop management system disturbances affect the AMF community is important for understanding and enhancing benefits provided by these important mutualists, and key to developing sustainable agro-ecosystems.

For this work I surveyed AMF community composition, structure, and AMF related functions in no-till, biologically-based/organic, early succession, and conventional management plots at the Kellogg Biological Station-Long Term Ecological Study Main Cropping System Experiment. I examined the effects of tillage and chemical inputs on AMF through an intensive sampling from 2010 to 2012. I also examined the historicaleffects of these different row crop agricultural management systems on AMF community and function by surveying archived soil samples taken annually following establishment of this site in 1989. Finally, I examined effects of the different management systems on the functioning of whole soil microbial communities in a controlled greenhouse experiment.

Overall, I found that AMF communities respond differently to tillage and chemical input disturbances associated with management. Although long term trends indicate a reduction in both AMF richness and diversity for all row crop management systems, short term richness and diversity were higher in conventional, organic, and reduced input plots, as compared to the no-till and early succession systems. I found AMF community structure to be differently affected by tillage and chemical inputs. For example, AMF community composition and structure was most similar between the conventional and no-till row crop systems, and the reduced input and organic systems, when controlling for year/crop effects, indicating an effect of chemical input on the AMF community. I found measures of AMF function, specifically plant root colonization, to be robust to management system inputs. Under row-crop management, ecosystem services linked to soil carbon sequestration and water-stable aggregate formation and provided by AMF derived soil glomalin, were lower in conventional compared to the organic systems. All active agricultural systems had lower levels of soil glomalin as compared to old fields (agricultural abandonment). My results suggest AMF community composition, structure, and function are altered by these different row crop agricultural management systems, and ecosystem services currently provided by AMF are limited by both historical (+100 years) and continued management input disturbances. Following total abandonment of agricultural management, there is some restoration of AMF community structure and function and increased AMF contribution to ecosystem services, but these improvements in function are likely not similar to the functioning of the original soil microbial community.

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