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Pett, Lindsey Ann

Biology

2022

Ph. D.

For the past century, inputs of nitrogen, phosphorus, and other nutrients to aquatic ecosystems have been chronically elevated by human activities. Nutrient loading occurs at multiple spatial scales, from the discharge of wastewater into individual river drainages to atmospheric inputs at the continental scale caused by the burning of fossil fuels and use of synthetic fertilizers. Ecosystem components such as producer or consumer populations may respond stoichiometrically, either by actively regulating nutrient uptake or passively absorbing nutrients from their altered environment. Ecosystems may also respond to elevated nutrients through changes in species richness, species composition, abundance, or biomass, and these effects may cascade through food webs that are linked through consumption. Understanding these effects in natural systems is challenging because there are large-scale gradients in nutrient deposition across latitude, elevation, and growing season length.In this study, I first quantified the responses of the micro-ecosystem of the carnivorous pitcher plant Sarracenia purpurea to experimental manipulations of nutrients. At the small scale of a single bog in northern Vermont, I manipulated nitrogen and phosphorous inputs and nutrient ratios in a replicated ecological press experiment, and measured nutrient uptake, biomass, and abundance of the various components of the Sarracenia micro-ecosystem. I also measured the same ecosystem components in a snapshot survey of 28 bogs from Florida to Maine. This transect encompassed geographic gradients of latitude, elevation, and growing season length, as well as gradients of annual atmospheric N and P deposition rates. I then compared the small-scale experimental effects of nutrient additions on ecosystem components to the large-scale correlations of annual N and P deposition rates with the same ecosystem components. I found strong concordance in both direction and magnitude of effects of nutrient deposition on pathways of nutrient transfer, but weaker effects on the trophic transfer of biomass and abundance. Pitcher fluid, which is analogous to lake and stream water in large aquatic ecosystems, tracked experimental manipulations and depositional gradients in phosphorus, which is consistent with nutrient dynamics of surface waters in undisturbed watersheds. Experimental and natural nutrient additions also affected the growth and morphology of the leaves of S. purpurea. Carnivorous traits such as relative tube diameter responded readily to increasing N deposition at both small and large spatial scales, highlighting a new pathway for nutrient deposition to affect ecosystem processes by altering the habitat volume for the entire ecosystem. I also filled knowledge gaps of the model system S. purpurea. Algal, cyanobacteria, and rotifer community structure within S. purpurea has been greatly understudied within S. purpurea's native range. My research presents the first large-scale survey of algal inhabitants of S. purpurea, in which plants acted like larger aquatic ecosystems that support diverse phytoplankton assemblages of algae, cyanobacteria, and aquatic invertebrates. For algal abundance, pitchers of S. purpurea were dominated by Chlorophyta in abundance whereas Cyanobacteria were dominant in biovolume. My final research aim was to determine whether the specialized invertebrate associates of Sarracenia represent a closed community after initial colonization, or whether Metriocnemus knabi aquatic larvae are capable of migration to new pitchers. With a manipulative greenhouse experiment, I provide the first evidence that aquatic larvae of M. knabi are capable of emigrating from unsuitable desiccated pitchers to suitable fluid-filled pitchers. Collectively, this uses the Sarracenia model system to gives new insights into ecosystem processes, biodiversity patterns, and dispersal potential.