Semester

Spring

Date of Graduation

2022

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Not Listed

Committee Chair

Ember Morrissey

Committee Co-Chair

Zachary Freedman

Committee Member

William Peterjohn

Committee Member

Louis McDonald

Committee Member

Edward Brzostek

Abstract

Human activities have led to profound changes in the climate and environment, fundamentally changing global carbon and nitrogen cycles. Ongoing conversion of wildland for human use and the intensification of agricultural systems have dire consequences for biodiversity and the ecosystem services that support society. While natural disturbance regimes are important for the long-term maintenance of native biodiversity and ecosystem function, many disturbances are becoming increasingly frequent due to anthropogenic activities. Increasing the frequency, intensity, or duration of disturbances can prevent ecosystems from returning to their previous equilibria. Disturbance-induced changes to the local environment shape microbial communities, which in turn govern ecosystem process rates, such as decomposition processes and nutrient cycling in soils and sediments. The composition and activities of these microbial communities are dependent upon the environment (moisture, pH, temperature, litter quality, etc.). Lastly, ecosystems rarely face individual disturbances, and the effects of multiple disturbances on biodiversity may be interactive and compounding. Therefore, it is imperative to understand the consequences of multiple disturbances on microbial habitats and communities. Thus, my research questions are: (1) How does land use in a mixed-use watershed shape stream chemistry and sediment microbial community composition?; (2) How does re-implementation of historical disturbances shape soil microbial community composition and nitrogen dynamics in a deciduous forest?; and (3) Do forest disturbance regimes affect the degree of physical protection conferred to soil carbon by aggregates? To address (1), I characterized stream water chemistry and sediment microbiomes along urbanization and agricultural gradients using an experimental mixed-use watershed in Morgantown, WV. I found that land use shaped stream water chemistry, sediment community composition and predicted function. I also found distinct microbial community thresholds along both urban and agricultural land use gradients. To address (2), I characterized the soil microbiome and key chemical parameters in the organic and mineral horizons of a long-term experiment re-implementing three historical disturbances (surface fire, herbivore exclusion, and canopy gap creation) in the Fernow Experimental Forest outside Parsons, WV. I found that all three disturbances shaped both soil chemistry and microbial community composition, with a legacy of fire being most influential. For example, a history of fire led to sustained increases in soil ammonium and nitrifying bacterial abundances. To address (3), I used size selective aggregate disruption of mineral soil from the same long-term experiment as above to test the importance of physical protection of soil carbon in aggregates under different forest disturbance regimes. I found that aggregate physical protection of soil carbon is significant, and that this protection may be more important in soils with a history of fire. Taken as a whole, this research provides consistent evidence that human activities are profoundly shaping the belowground chemical environment, microbial community composition and the cycling of carbon and nitrogen. These findings are increasingly relevant in the face of increasing human modifications to the environment and disruption of historical disturbance regimes.

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