Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Second Advisor

Dr. Rebecca Drenovsky

Abstract

Traits that increase mean nutrient retention times are essential to plant performance in low resource environments, where multiple stressors (low water and nutrients) are present. Although physiological responses to either water or nutrient stress are well understood, fewer studies have investigated the interaction of these stressors from a phylogenetically-controlled, whole-plant perspective. This research focused on three, phylogenetically-controlled pairs of shrubby evergreen species from the California chaparral that either grow on or off serpentine soils, which differ in nutrient availability. Using greenhouse and field studies, the responses of these plants to altered water and nutrient availability were evaluated. The greenhouse study addressed trade-offs among nutrient conservation traits, trait plasticity in response to resource availability, and instantaneous measures of plant stress to increased water and nutrients. The responses of the greenhouse-grown juvenile plants were then compared to juvenile plants growing in the field. I hypothesized that: 1) all species would respond positively to increased water and nutrients by increasing biomass production and having higher rates of gas exchange and nutrient use; 2) faster growing species would exhibit a larger degree of plasticity; and 3) there would be an effect of phylogeny among congener pairs. Juvenile species’ trait responses were negatively affected by increased water but not by increased nutrients, and faster growing species generally exhibited higher plasticity. Additionally, phylogeny constrained how these traits respond to environmental changes. Future research will be 6 crucial to the California chaparral and other low-resource ecosystems as anthropogenic environmental changes continue to accelerate their impact potential, especially near biodiversity hotspots.

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