Master of Science, University of Toledo, 2022, Biology (Ecology)

Atmospheric carbon dioxide (CO2) concentrations are increasing and may exceed 800 ppm by 2100. This is increasing global mean temperatures and the frequency and severity of heatwaves. Recently, it was shown for the first time that the combination of chronic warming and elevated carbon dioxide (eCO2) caused extreme upward bending during growth (i.e., hyponasty) of leaflets and leaf stems (petioles) in tomato (Solanum lycopersicum), which reduced growth. However, that study examined only two levels of CO2 (400, 700 ppm) and temperature (30, 37oC) at the young vegetative plant stage. Further, they did not investigate underlying mechanisms for this warming + eCO2-induced hyponasty, which is likely to involve the plant hormones auxin and ethylene, based on their role in thermal hyponasty. In this study, warming + eCO2 hyponasty was evaluated in tomato across a range of temperatures and CO2 concentrations, and at multiple life stages. Ethylene tomato mutants were examined to explore the potential role of these hormones in warming + eCO2 hyponasty. Lastly, other species were examined to test the hypothesis that warming + eCO2 hyponasty is restricted to compound-leaved species in this family. At eCO2 (800 ppm), petiole angle increased ca. linearly as temperature increased from 30-38oC. Under heat stress (HS, 38°C), petiole angle increased at all eCO2 concentrations compared to ambient (600/800/1000 vs. 400 ppm). All life stages examined (juvenile, pre-reproductive, and flowering) had increased petiole angle in leaves developed during warming + eCO2, such that most leaves exhibited hyponasty in juvenile plants but only young leaves did so in adults (previously fully-developed leaves were unaffected). Ethylene-insensitive (nr) and -constitutive (epi) mutants displayed similar changes in petiole angle with warming + eCO2 compared to the non-mutant reference (cv. Celebrity), indicating that ethylene is not a main component of the mechanism of this hyponastic response. (open full item for complete abstract)

Committee: Scott Heckathorn Dr. (Committee Chair); Heidi Appel Dr. (Committee Member); Jennifer Boldt Dr. (Committee Member) Subjects: Agriculture; Agronomy; Biology; Botany; Climate Change; Ecology; Environmental Science; Forestry; Morphology; Physiology; Plant Biology; Plant Sciences

Doctor of Philosophy, University of Toledo, 2020, Biology (Ecology)

Atmospheric carbon-dioxide (CO2) enrichment is largely the cause of current global warming. Hence, in the future, organisms will experience the interactive effects of elevated CO2 (eCO2) and chronic warming rather than their individual effects. Though individual effects of eCO2 or chronic warming on plant responses have been studied in some detail, interactive effects of eCO2 and chronic warming on plant responses such as nitrogen (N) relations (uptake, translocation, assimilation) and leaf hyponasty (upward bending of leaves) have been rarely studied. Therefore, the goals of my dissertation work included (1) investigation of eCO2 plus chronic warming on plant N relations, using tomato (Solanum lycopersicum L. cv. Big Boy) and wheat (Triticum aestivum L. cv. Glenn) followed by a meta-analytic review, and (2) investigation of eCO2 plus chronic warming on leaf hyponasty and subsequent effects of hyponasty on plant growth, using tomato and other economically-important species. These goals were achieved by growing plants in a full-factorial experimental design, using two levels of CO2 (ambient vs. elevated) and two temperature regimes (near-optimal vs. supra-optimal) in controlled-environment growth chambers. In all experimental trials conducted, eCO2 plus warming inhibited tomato vegetative growth, whereas warming alone inhibited growth to a smaller extent, and eCO2 alone increased growth. One potential reason for inhibition of plant growth at eCO2 plus warming could be the observed increase in leaf hyponasty. Warming or eCO2 alone caused modest leaf hyponasty, whereas eCO2 plus warming caused severe leaf hyponasty, which correlated with decreased leaf area and biomass. This could be explained by decreased light interception, and thus in situ photosynthesis, as leaves became more vertically-oriented. Severe hyponasty driven by eCO2 plus warming was observed only in the compound-leaved species tested, but not in the simple-leaved species tested. Tomato plants grown at e (open full item for complete abstract)

Committee: Scott Heckathorn (Committee Chair); Heidi Appel (Committee Member); Jennifer Boldt (Committee Member); Michael Weintraub (Committee Member); John Gray (Committee Member); Maria Bidart (Committee Member) Subjects: Agriculture; Biochemistry; Biology; Botany; Climate Change; Ecology; Environmental Science; Physiology; Plant Biology; Plant Sciences