Physiological response of grassland species to variable water supply and demand

Rueda, Austin James (2019) Physiological response of grassland species to variable water supply and demand. Masters thesis, Northern Arizona University.

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Abstract

The US Southwest is predicted to experience longer periods of drought with more intensive monsoonal precipitation during the summer months in the near future. These changes in precipitation may drastically alter grassland ecosystems in terms of community composition, net primary production, and physiological performance of plants. Greater precipitation and increased soil moisture allow plants to uptake more water and open their stomates, allowing for gas exchange. Conversely, greater vapor pressure deficit (VPD) typically corresponds with the closure of stomates to protect xylem from cavitation due to excessively negative osmotic pressure. By experimentally altering summer precipitation in grassland ecosystems ranging from desert scrub to mixed conifer forest meadows, we provide lines of evidence that suggest that the interactive effects of soil moisture (water supply) and VPD (water demand) do affect the stomatal conductance (gs) and gas exchange strategy of dominant species. As expected, soil moisture was positively correlated with gs while VPD showed a negative correlation across all ecosystem types. Lower elevation ecosystems were typically more regulated by water demand, where grasses and displayed an avoidance strategy to increased water demand by closing their stomates to conserve water and avoid xylem cavitation. Grasses become less water limited with increasing elevation and do not regulate gas exchange as tightly with increasing VPD. In the systems where the interactive effect of water supply and demand was a significant predictor of gs variance, higher elevations switched from an avoidance strategy with increasing VPD, to a tolerance strategy, increasing gs when both water supply and demand are high. The results of this study indicate that the interactive effects of water supply and demand will be crucial predictors of ecosystem response to changing climates, and the strategies employed by plants will vary with elevation and ecosystem type.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	elevational gradient; Gas exchange; precipitation; stomatal conductance; vapor pressure deficit; Grassland; Southwest; Ecosystem management
Subjects:	Q Science > QK Botany
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Biological Sciences
Date Deposited:	28 Jan 2022 23:41
Last Modified:	28 Jan 2022 23:41
URI:	https://openknowledge.nau.edu/id/eprint/5601

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