Date on Master's Thesis/Doctoral Dissertation

8-2024

Document Type

Master's Thesis

Degree Name

M.S.

Department

Biology

Degree Program

Biology, MS

Committee Chair

Mehring, Andrew

Committee Co-Chair (if applicable)

Yanoviak, Steve

Committee Member

Yanoviak, Steve

Committee Member

Thompson, Aaron

Author's Keywords

greenhouse gas; phosphorus fractionation; zoogeochemistry; soil fauna; carbon cycling; formicidae

Abstract

This thesis contains four individual chapters, two of which highlight studies assessing how arthropods contribute and drive geochemical transformations by directly and indirectly manipulating the availability of anoxic conditions. The first chapter serves as an introduction to the literature on the subject to contextualize the work carried out in later chapters. The second chapter is a field study conducted throughout the summer of 2023 in a lowland tropical rainforest in Costa Rica, where I characterized the temporal and environmental variation impacting greenhouse gas emissions from the nests of leaf-cutting ants (Atta cephalotes). From flux measurements taken across 29 individual nests, I found evidence that leaf-cutting ant nests appear to allow enhanced methane (CH4) oxidation under dry conditions, such as the drought, which impacted the area during most of the study period. However, I found that nests are capable of inverting to net CH4 sources within as little as four weeks if soil moisture is restored, suppressing oxidation within nest tunnels, and thus restoring more prevalent anoxic conditions. The third chapter complements the themes of the second through a lab study, where millipedes were placed within soil microcosms to measure their anoxic gut’s ability to liberate vii phosphorus (P) bound to iron (Fe). While I did not find evidence supporting the millipedes’ gut microbiome making Fe-bound P more available, they still managed to reduce other portions of non-apatite inorganic P in soil. Further, they reduced soil carbon and nitrogen levels, most likely through the consumption of organic matter. The final chapter highlights overlap between the previous two and provides commentary on improvements and further avenues of inquiry. Overall, the work presented here exemplifies a growing field of study surrounding animal-mediated biogeochemical cycles, with an emphasis on how soil arthropod ecology and physiology can help drive unique transformation under anoxic conditions.

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