Date of Award

Spring 1-1-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Jason Neff

Second Advisor

Eve-Lyn Hinckley

Third Advisor

Katharine Suding

Abstract

Mountainous ecosystems are expected to have longer, warmer and drier growing seasons in the future. In this thesis, I examine how climate change may differentially affect two plant community types in the alpine tundra: conservative plant species characteristic of the dry meadow and acquisitive plant species characteristic of the wet meadow. I develop and use a photosynthesis-stomatal conductance model to explore how abiotic conditions, i.e. air temperature and soil moisture, and leaf traits, e.g. the leaf nitrogen content and plant height, govern conservative and acquisitive species’ assimilation. The model is parameterized and validated with data obtained at the Niwot Ridge Long Term Ecological Research site. Model results produce realistic estimates of photosynthesis, nitrogen-use efficiency, water-use efficiency and other gas-exchange processes in the alpine tundra. Model simulations suggest that changes to soil moisture do not affect conservative and acquisitive species’ rate of assimilation. Instead, the two communities respond to variation in foliar nitrogen content and air temperature. However, conservative and acquisitive species do not equally respond to increased temperatures during a longer growing season because of differences in the leaf temperature which is, in turn, affected by the interaction of plant height and microclimate. If plant foliar nitrogen content varies similarly across the two communities, then differences in air temperature optima between conservative and acquisitive species may contribute to inter-specific competition. Simulations of potential future climates indicate that higher temperatures and a longer summer could favor acquisitive species and, thus, may contribute to changes in the relative abundance of conservative and acquisitive species in the alpine tundra.

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