Doctor of Philosophy (PhD)
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If one wishes to understand the ecological role, range, habitat preferences, selective pressures, reproduction, response to climate change, and the potential for survival under climactic change, range expansion and range contraction for species and populations of bryophytes, an understanding of their survival of the desiccated state, is essential. In order to further our understanding of desiccation tolerance in mosses, three projects were undertaken. The first of these investigated the nature of desiccation tolerance in mosses, specifically if desiccation tolerance can be induced; thereby providing a desiccation tolerant phenotype in a moss species generally considered desiccation sensitive (Physcomitrella patens, the model organism for mosses). This hypothesis supposes the traditional dogmatic assumption that mosses can be cleanly divided into two categories (desiccation tolerant or desiccation sensitive) is wrong. The second project expanded upon the first by investigating if a hardened desiccation tolerant phenotype is retained for a time following the cessation of stimuli (using P. patens as a study system). The third project was designed to disentangle the interacting factors of ecotypic variation in Bryum argenteum (both in mean trait values as well as phenotypic plasticity), rate of desiccation (time allotted for the induction of desiccation tolerance), and life history phase (five categories considered).
Inducible desiccation tolerance exists in mosses and the examined―desiccation sensitive species can survive desiccation if given proper stimuli, refuting the conventional dogma of desiccation tolerance existing as a binary state of tolerant or sensitive. Hardening toward desiccation tolerance was shown for P. patens, attenuating within eight days. All factors examined within the third study (rate of drying, phase, and ecotype) proved to significantly impact desiccation tolerance. Adult shoots and bulbils (lateral dispersal agents across a local landscape, vegetative propagules) were found to display a desiccation tolerant phenotype with either rapid or no required induction for all ecotypes examined. Juvenile and intermediate shoots displayed an inducibly desiccation tolerant phenotype in response to the rate of drying applied (longer times resulting in greater health upon rehydration), with variation in response detected between ecotypes examined. For some juvenile and shoot ecotypes a rather low inducible capacity was shown requiring long rates of drying to achieve a high degree of desiccation tolerance, other ecotypes however displayed either a strong inducible response requiring only a short rate of drying for induction. The protonemal phase (responsible for lateral growth across the substrate, and giving rise to shoots) showed a pattern similar to juveniles, but more pronounced with more damage apparent with rapid dries. Some protonemal ecotypes did not appear to respond to slower dries, apparently lacking an inducibly desiccation tolerant phenotype, while some ecotypes (typically from the Southwestern United States of America; CA, NM, NV) showed a high potential for rapid induction of a desiccation tolerant phenotype. These results are interesting as they show a wider breadth of capacity for desiccation tolerance in regards to desiccation tolerance as well as a varying capacity for the phenotypic plasticity in response to slow drying rates for induction.
Bryophyte; Bryum argenteum; Chlorophyll fluorescence; Desiccation; Physcomitrella patens; Stress Tolerance
Biology | Botany | Medical Physiology | Physiology
University of Nevada, Las Vegas
Greenwood, Joshua Lee, "Factors Influencing Induction of Desiccation Tolerance in Bryophytes: Redefining Fundamental Aspects of the Organism’s Relationship with the Environment in Xeric Habitats" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 2977.
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