DISSERTATION RESEARCH: Interactive Effects of Fern and Microbial Stoichiometry on Decomposition

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Plants and the microorganisms that decompose them innately contain different amounts of elements such as carbon, nitrogen and calcium. The time it takes for the microbial community to break down plant material is often correlated with plant nutrient concentrations; plants with nutrient concentrations closer to that of fungi and bacteria decompose faster. Because decomposition ultimately controls nutrient availability to plants, understanding why different types of plants decompose differently is important. Distinct plant groups can have different nutrient concentrations that may contribute to differences in decomposition rates. Ferns are a significant component of many terrestrial forests, and often decompose more slowly than angiosperms. Ferns also appear to be nutrient-poor in comparison to angiosperms, and those ferns species that evolved longer ago are nutrient-poor in comparison to evolutionarily younger fern species.In order to test the importance of nutrient content for fern decomposition, we will explore decomposition dynamics of ferns and angiosperms in the laboratory, where we will manipulate the nutrient content of both leaves and soil. Measurements of microbial community composition and leaf elemental content over time will clarify the interactions between nutrient content, fungal/bacterial ratios, and nutrient release and decomposition rates. Stable isotopes of elements such as nitrogen and calcium can be used to trace the movement of nutrients; we will add stable isotopes to the soil in a subset of the experiment, thereby tracking microbial movement of nutrients into decomposing leaves. Additionally, we plant to directly analyze microbial nutrient content using an x-ray attached to a scanning electron microscope. These techniques will further illuminate the fates of nutrients and the influence of plant and soil nutrient content on microbial nutrients.