Date of Award

5-2024

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Environmental Biology

First Advisor

Rick Kesseli

Second Advisor

Robert Chen

Third Advisor

Luis De Leon Reyna, Aaron M. Ellison

Abstract

Carnivorous plants are insectivorous plants that have reversed the evolutionary paradigm of “Insects eat plants'' to “Plants eat insects”. Carnivorous plants thrive in pristine, nutrient-poor wetlands and trap and digest small animal prey to compensate for the lack of nutrients in the environment. Such nutrient-deprived oligotrophic habitats where carnivorous plants occur are some of the most important ecosystems for human communities. However, these freshwater wetlands are increasingly under threat from eutrophication, an input of reactive nutrients, such as nitrogen (N) and phosphorus (P). The increased flux of available N and P caused by human activities is impacting biodiversity of wetlands at different scales, different groups of organisms, and different trophic levels. Therefore, it is imperative that the nutrient levels of these wetlands be monitored, and the ecosystem protected. Interestingly, carnivorous plants are known to change their "degree of carnivory" depending on the availability of nutrients in the environment, and thus can be a potential tool to monitor the nutrient changes in wetlands. The first chapter focusses on carnivory in Utricularia spp. (bladderwort) in Australia, aquatic carnivorous plants that use underwater bladder traps to capture and digest aquatic invertebrates. The work described in this chapter was carried out in collaboration with the Centre for Coastal Biogeochemistry (CCB) in New South Wales, Australia through the Limnology and Oceanography Research Exchange (LOREX) program of the National Science Foundation. We measured the relationship between carnivory in Utricularia spp. and the level of nutrients in its natural habitat using stable nitrogen abundance isotope ratios (δ15N). Carnivory provided 40 –100% of the plant’s nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon in the water. Our findings suggest that Utricularia populations may acclimate to high nutrient environments by shifting away from an energetically costly carnivory. This raises questions as to what drives the loss of Utricularia spp. commonly observed in eutrophic waterbodies. The second chapter focuses on three genera of local carnivorous plants, Sarracenia purpurea (American pitcher plant), Drosera intermedia (sundew), and Utricularia inflata (bladderwort). Little is known about the seasonal diet shifts between carnivory and the abiotic environment as sources of nutrients among co-occurring carnivorous plant species. Although studies reporting captured prey species by carnivorous plants are abundant, studies investigating the composition of assimilated prey species in their leaves are scarce. I investigated the spatiotemporal dynamics in carnivory vs. environmental nutrient acquisition and compositional analysis of prey species assimilated in carnivorous plants of New England (USA). I measured the natural abundance stable isotope ratios of the above species and their nutrient sources during their growing seasons in two oligotrophic ponds in New England. MixSIAR, a Bayesian stable isotope mixing model, was used to estimate the carnivory of each plant species and the composition of prey species assimilated in terrestrial carnivorous plants. Spatiotemporally, aquatic U. inflata acquired more nutrients from carnivory (70 to 100%) than did terrestrial carnivorous plant species (29% to 63%). S. purpurea acquired nutrients mainly from ants and flies. The sources of nutrients for D. intermedia varied spatiotemporally among arthropod species. The large contribution of carnivory to the nutrient budget of U. inflata could be a result of its lack of roots and high metabolic rate. S. purpurea and D. intermedia could effectively regulate the nutrient level in their habitat or benefit from environmental dissolved organic nitrogen. The results of the study of prey proportions can be used as the first available prior information for Bayesian approach in future studies. As anthropogenic driven nutrient influx continues to cause eutrophication globally, unique, and rich wetland biodiversity is altered and is diminishing rapidly. Thus, understanding the sources of nutrients in carnivorous plants can provide invaluable insight into the ecophysiology and conservation of carnivorous plants and their fragile wetland ecosystems.

Comments

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