Browsing Master's Theses by Authors
Symbiosis in the Context of an Invasive, Non-Native Grass: Fungal Biodiversity and Student EngagementArnold, Anne E.; Lehr, Gavin Charles; Arnold, Anne E.; U'Ren, Jana M.; Rosenzweig, Michael L.; Elfring, Lisa K. (The University of Arizona., 2018)Grasslands in the western United States face severe environmental threats including those brought about by climate change, such as changes in precipitation regimes and altered fire cycles; land-use conversion and development; and the introduction, establishment, and spread of non-native species. Lehmann’s lovegrass (Eragrostis lehmanniana) was introduced to the southwestern United States in the early 1900s. Since its introduction, it has become the dominant grass in the mid-elevation grasslands of southern Arizona, including the Santa Rita Experimental Range (SRER), where it has displaced native grasses including Arizona cottontop, three awns, and gramas. Like all plants in terrestrial ecosystems, this grass harbors fungal symbionts that can be important for its establishment and persistence. This thesis focuses on fungal symbionts of Lehmann’s lovegrass and has two components. First, the diversity and distributions of endophytes in Lehmann’s lovegrass are evaluated in the context of biotic and abiotic factors in the SRER. Culturing from roots and shoots of Lehmann’s lovegrass at points beneath and outside the canopy of native mesquites, which are encroaching on grasslands over time, provides insight into how a single plant species can exhibit local variation in the composition of its symbionts. Second, the thesis is used as the basis for engagement of students in science, technology, engineering, and mathematics (STEM) through the development and implementation of classroom- and field activities centered on endophytes, which help high school students address core learning aims while also gaining real research experience. Engaging students in important questions relevant to their local environment can catalyze interest in science and help students cross the threshold into research. The contributions of such approaches with respect to learning not only fulfills key next-generation science standards and common core objectives, but provides students with a meaningful introduction to the excitement, importance, and accessibility of science.
The Composition and Diversity of Volatile Organic Compounds (VOCs) From Leaf Litter in the Biosphere 2 Tropical RainforestU'Ren, Jana M.; Crocker, Lia Noel; Meredith, Laura; Hurwitz, Bonnie (The University of Arizona., 2021)Background: Volatile Organic Compounds (VOCs) are organic compounds with high vapor pressure at room temperature released by plants, bacteria, archaea, fungi, and protists. Plants and microbes can produce VOCs as a means of communication (i.e., signaling and species interactions) or as a mechanism to ameliorate abiotic stress (e.g., isoprene with high temperatures). The majority of microbial VOC (mVOC) studies have focused on volatiles produced from soils, but recent evidence suggests that leaf litter can have greater VOC production, microbial biomass, and respiration rates adjacent soil. However, it is difficult to differentiate plant VOCs from mVOCs and identify the different mechanisms driving their release into the atmosphere. Thus, as part of an ecosystem-scale project at the Biosphere 2 Tropical Rainforest (B2 TRF) that addressed the impact of drought on VOCs from soil and living leaves (i.e., Biosphere 2 Water, Atmosphere, and Life Dynamics: B2 WALD), I performed a 10-day VOC experiment of leaf litter to: (i) quantify and identify VOCs produced by Clitoria leaf litter in B2TRF; (ii) examine the impact of moisture on litter VOC flux; and (iii) determine whether flux patterns can be used to distinguish plant VOCs and mVOCs. Methods: Leaf litter was collected from five individuals of Clitoria fairchildiana distributed across the B2 TRF. VOCs were continuously measured over a 10-day period from four replicate chambers and a control chamber using proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). To examine the impact of moisture on VOC fluxes, leaf litter was wet after seven days to simulate a rainfall event. VOCs were identified by comparing each mass to a reference database and flux calculations were performed to examine change in VOC abundance over time, after accounting for the control. Results: In total, 304 VOCs were identified across all four replicate chambers. Wetting altered the flux of 35% of litter VOCs. Among VOCs emitted after wetting, 72 decreased to pre-wetting levels within 24 hours, while 25 sustained higher production with increased moisture. Conclusions: Leaf litter represents a significant source of VOCs yet even with high resolution real-time data it is difficult to differentiate plant-derived VOCs from mVOCs due to shared metabolic pathways, as well as limited information on mVOCs. In addition, although I hypothesized that wetting would stimulate mVOC production, strong fluxes of VOCs after wetting were likely plant-derived VOCs whose release from the leaf surface was amplified by Henry’s law. Future work is needed to identify mVOCs from microbial cultures and link to leaf-level measurements.