Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Steven K. Schmidt

Second Advisor

William D. Bowman

Third Advisor

Noah Fierer

Abstract

Periglacial ecosystems can be found on every continent and represent life's coldest terrestrial foothold, yet their ecology is rarely studied. These areas are subject to the harsh environmental stressors of a short annual photosynthetically active period, high solar radiation, high temperature variability, low soil development, and low humidity. This research takes advantage of these environmental stressors to address one central thesis: sampling across multiple spatial scales and environmental gradients will quantify the relative strength of biological and environmental factors shaping periglacial ecosystems. The results demonstrate that periglacial soils harbor the lowest microbial biomass and dissolved nutrient levels of any terrestrial environment that supports life. In general, the abundance of microbes in these soils is positively correlated with soil water content and water holding capacity. However, tropical periglacial soils from Perú had higher average microbial biomass than temperate zone soils from Colorado, Nepal, Argentina, and Alaska despite the relatively dry soil conditions and high altitude of the Peruvian soils. Periglacial soil microorganisms also persist at a surprisingly high microbial biomass C:N ratio in spite of low soil dissolved C:N ratios, which is suggestive of a soil stoichiometry that is greatly divergent from that observed in vegetated systems. This divergence is likely due to microorganisms accumulating high concentrations of drying/freezing protection oligosaccharides in order to survive in the harsh periglacial environment. Soil bacterial communities in the periglacial soils of Green Lakes Valley, Colorado showed strong spatial autocorrelation in community composition up to a distance of 240 meters that was driven by changes in the relative abundance of specific bacterial clades across the landscape. Analysis of clade habitat distribution models and spatial co-correlation maps identified soil pH, plant abundance, and snow depth as major variables structuring bacterial community composition across this landscape and revealed an unexpected and important oligotrophic niche for the Rhodospirillales in soil. Furthermore, the global analysis of periglacial soils from Argentina, Colorado, Nepal and Alaska shows that habitat distribution models for bacteria have strong predictive power across the entire globe. This multi-scale approach yields important insights into the fundamentals soil microbiology and, ultimately, a greatly improved definition of periglacial ecology.

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