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Pennsylviana State University (2012)

Mitigation of drought-induced reductions in wild oat seed quality by elevated carbon dioxide

Granger, Kristen Louise

Titre : Mitigation of drought-induced reductions in wild oat seed quality by elevated carbon dioxide

Auteur : Granger, Kristen Louise

Université de soutenance  : Pennsylviana State University

Grade : Doctor of Philosophy (PhD) 2012

The goal of this dissertation was to elucidate the mechanisms contributing to seed persistence in the soil, and subsequent plant fitness, using wild oat (Avena fatua L.) as a model species. Experiments examined the effects of elevated carbon dioxide and drought during seed maturation on wild oat fecundity and seed quality (as measured by chemical composition, dormancy levels, and resistance to microbial decay and aging). It was hypothesized that elevated atmospheric carbon dioxide would mitigate drought-induced reductions in seed quality, increasing seed size and production, enhancing dormancy levels and conferring greater resistance to microbial attack and age-related deterioration. A related goal was to determine the accuracy and specificity of spectrophotometric methods of determining phenolic concentrations, by comparison to gas chromatography-mass spectrometry. It was hypothesized that the spectrophotometric assays would be less accurate in quantifying total phenolic concentration, depending on the specificity of the reagents. In addition, it was hypothesized that the different extraction procedures used in conjunction with the spectrophotometric assays would lead to differential extraction and measurement of phenolic compounds. For the methods comparison experiment, it was found that the spectrophotometric methods significantly overestimated phenolic concentrations compared with GC-MS analysis, with concentrations that were 0.005- 12% of the totals indicated by GC-MS. In addition, the simpler extraction procedures recommended for the spectrophotometric analysis did not extract bound compounds, thereby missing a major portion (up to 98%) of the phenolic constituents. Therefore, it was determined that GC-MS analysis and extraction of the bound phenolics was appropriate in order to study the chemical composition of seeds. Analysis of the organic acid constituents of wild oat revealed that elevated carbon dioxide appeared to affect the concentrations of phenolic, aliphatic and long-chain fatty acids in the 2009 SH430 line, but drought and carbon dioxide appeared to have little affect on concentrations in the 2010 experiment. As expected, carbon dioxide did mitigate the effects of drought on reproductive output and dormancy to some extent, causing a 49% increase in seed biomass per plant regardless of drought treatment and increasing the percentage of dormant seeds by 10% after 12 weeks of after-ripening. Contrary to the hypothesis, however, drought and elevated carbon dioxide did not appear to affect seedling vigor or susceptibility to aging. Aging had a consistent impact on seedling vigor and resistance to microbial decay, increasing the number of days to emergence, decreasing seedling biomass per treatment, and enhancing microbial decay (up to 118%). The results of these experiments show that elevated carbon dioxide and drought can have significant effects on seed quality characteristics and that future climatic conditions could allow weedy and invasive species to produce greater numbers of more dormant seeds, establishing more persistent seedbanks that could pose management issues for farmers


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