Biology ETDs

Publication Date

12-1-2015

Abstract

Arid ecosystems are home to approximately 35% of earth's human population, and approximately 40% of earth's terrestrial carbon. These systems are especially prone to releasing the stored carbon when under global climate change (GCC) related pressures. My goal for these studies was to expand on our already growing knowledge base of how the soil microbial communities in disturbed arid ecosystems undergo shifts in functional patterns, as they respond to a rapidly changing environment. In chapter two, I examined the overall functional activity levels and functional behaviors exhibited by both pinon and juniper supported RAM communities in the context of widespread, disproportionate pinon mortality. More specifically, I examined the rhizosphere level effects of various types of nearest neighbor competition and tree physiological status on RAM functional behaviors and activity rates, after all pinon trees >7cm diameter at breast height had been girdled. From our girdled site results, we observed higher plant cell wall related decomposition activities under live juniper canopies, compared to dead piñon trees. In contrast, at the control site, we observed higher plant cell wall decomposition rates under live piñon rather than juniper canopies, particularly with higher soil moisture availability. Additionally, the ordination plots for intact PJ woodlands show a decreasing trend in microbial cell wall decomposition activity as soil water availability and fungal biomass increased. We observed the opposite trend at the girdled site. For chapter three, I expanded analyses of the data presented in chapter two by performing three different multivariate statistical methods in an effort to explain how widespread pinon mortality events affect the interactions between numerous soil parameters and multiple aspects of RAM soil activity behaviors. I also used data from an additional study conducted at a nearby juniper savannah to serve as a reference for the directions the RAM activity trends at mortality affected pinon juniper woodland sites could take, as the dead pinons give way and junipers take over. In general, results from these two chapters suggest that widespread piñon mortality significantly affects the functional behavior of rhizosphere microorganisms at multiple scales, in part by shifting the focal substrates of microbial community decomposition. For chapter four, I sought to address questions regarding the effects of other types of GCC related disturbances, e.g., shrub encroachment and fire, on the RAM communities on three other types of arid biomes: grasslands, shrub-lands and shrub-grass ecotone. With this study, the results also show the ability of different types of disturbance events to disrupt the previously established relationships between soil parameters and RAM activity patterns. The results from this chapter suggest that observed changes in EEA profiles may be related to the dominant plant functional type and the mechanism of disturbance that each biome type has encountered.

Language

English

Keywords

piñon mortality, extracellular enzyme activity, root associated microbiota, disturbance, structural equation model

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Litvak, Marcy

Second Committee Member

Takacs-Vesbach, Cristina

Third Committee Member

Gehring, Catherine

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