Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Ecology and Evolutionary Biology

Major Professor

James A. Fordyce

Committee Members

Susan Kalisz, Jen A. Schweitzer, Sarah L. Lebeis


With the development of next generation sequencing technology, ecologists have recently been able to describe microbial communities across a wide array of niches at an accelerated pace. De-novo-based patterns in richness and relative abundance have been described for bacterial and fungal communities in terrestrial, aquatic, and host-associated microhabitats. A recent synthesis has shown that these communities exhibit similar geographical patterns that have been traditionally described for plant and animals. Yet, there is a lack of hypothesis-based research for host-associated microbial communities. Throughout this dissertation, I will address how spatial scale, sequencing resolution, and manipulative rainfall exclusion govern host-associated microbial communities in the rhizosphere microhabitat. Further, I will show how ecological niche modeling predicts the most important climatic variables that circumscribe the distribution of an obligate ectomycorrhizal (EM) fungus and its host. First, rhizosphere bacterial communities are spatially distinct in terms of composition and alpha diversity along the root length. In this microhabitat, the data shows a positive Species-Area Relationship. Second, combining discrete, fine grain samples in silico can capture greater richness estimates across a spatial scale within a host specific environment. Third, dominant and rare bacterial taxa respond to both rainfall exclusion and the log of phosphorous and ammonium throughout the monsoon season in the Sonoran Desert. Dominant bacterial taxa might be responsible for observed variation in beta diversity among rainfall exclusion treatments. Arbuscular mycorrhizal fungal communities are temporally dependent and respond to rainfall exclusion throughout the monsoon season. Moderate rainfall exclusion hosts more ecologically diverse communities than no exclusion or extreme exclusion to rainfall. Lastly, in current climate conditions, I showed that like plants and animals, temperature and precipitation can be the most important predictors of fungal distributions. Across all future climate scenarios, predicted habitat of EM fungi was seen to decrease more than that of its host. Results shown throughout these studies illustrate the importance spatial scale, sequencing grain, and abiotic conditions have on microbial community richness, as well as microbial persistence under changing soil moisture and future climate scenarios.

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