Microbial communities are ubiquitous in our world and play important roles in biogeochemical and ecosystems processes on Earth. The ability of these microbial communities to provide these different processes is frequently tied to their community structure, which can be thought of both in terms of membership (i.e. who is there) and the relative abundance of these members. Changes in environmental conditions often lead to changes in microbial community structure as well. Microbial communities are formed through the process of assembly, which in turn is driven by the four processes of 1) Selection 2) Dispersal 3) Drift and 4) Diversification. Understanding the relative importance of each of these processes in different systems is important for predicting how microbial communities will change in response to disturbances. This dissertation presents work that uses the coal fire in Centralia, PA as a model press disturbance for understanding soil microbial community responses to and recovery from disturbance. The experiments herein aim to shed light the relative roles of Selection, Dispersal, and Drift in governing these responses in soil microbial communities experience a temperature disturbance. An observation study of a chronosequence of fire disturbance in Centralia, PA is used to generate hypotheses as to the relative roles of Selection, Dispersal, and Drift in the assembly of soil microbial communities experiencing a temperature disturbance. Further, an in depth look at some of these communities using shotgun metagenomics is used to observe specific microbial traits and characteristics selected for by the temperature disturbance. Finally, a laboratory soil mesocosm warming experiment investigates the relative influence of Dispersal and dormancy in governing responses to and recovery from disturbance.

Soil microbial communities were examined in two chronosequences of reclaimed surface mine soil and in a chronosequence of previously burned sites to determine how these communities recover through time after disturbance. Phospholipid fatty acid (PLFA) methods for microbial community analysis were used to quantify microbial biomass, diversity, and abundance of specific microbial groups (gram positive bacteria, gram negative bacteria, fungi, arbuscular mycorrhizal fungi, and actinomycetes). Multivariate analysis of variance (MANOVA) and discriminant analysis (DA) were used to compare soil microbial communities and site environmental factors. The soil microbial community in sagebrush-grassland ecosystems disturbed by fire appeared to recover to similar levels of biomass and diversity as in unburned soil within 3 to 7 years. In the surface mine reclamation sites, microbial recovery was seen in 5 to 10 years after reclamation in sites dominated by sagebrush and within 14 years after reclamation in the sites dominated by cool season grasses. Plant community composition was found to have influences in soil microbial recovery. Microbial communities in soil under crested wheatgrass (Agropyron cristatum) recovered to greater biomass than did the communities associated with other plant species. Soil fungi appeared to be the most adversely affected by soil disturbance associated with surface mining than the other microbial groups examined, and they were also slow to recover after the initiation of reclamation. A general trend of recovery towards the undisturbed condition with reclamation age was found for all microbial groups after disturbance. Our data on microbial community recovery from fire and impacts of surface mining suggests that soil microbial communities are highly resilient to disturbances.

Understanding the response of soil microbial communities and decomposition to global environmental changes is central to our ability to accurately forecast future terrestrial carbon (C) storage and atmospheric CO2 levels. Increases in the frequency and severity of disturbance events are one element of global change in terrestrial ecosystems. The goal of this dissertation was to measure the response of soil microbial communities and decomposition to disturbance events and to examine the mechanisms underlying post-disturbance changes in decomposition. In the first part of my dissertation work I explored these questions within the context of wildfires in boreal forests. Chapter 1 characterized soil microbial communities and the rate of decomposition across a fire chronosequence in interior Alaska. I found that boreal forest fires reduced soil microbial abundance, altered fungal community composition, and suppressed litter decomposition. Chapter 2 investigated whether soil microbial responses to boreal forest fires differ as a function of fire severity. I demonstrated that higher severity fires elicited greater reductions in soil microbial biomass and larger shifts in fungal community composition than lower severity fires. Chapter 3 tested the mechanisms through which boreal forest fires alter decomposition processes. I discovered that decomposition rates were slower in recently burned forests because of post-fire reductions in soil moisture and C substrate quality. In the second part of my dissertation I expanded my findings to other types of disturbance events using meta-analysis. Chapter 4 reviewed the response of soil microbial biomass to fires. I found that soil microbial biomass was significantly lower in recently burned ecosystems, but the response of microbial biomass to fire differed by fire type and biome. Chapter 5 examined soil microbial responses to abiotic (fire, harvesting, storms) and biotic (insect infestation, pathogen outbreaks) disturbances in forests. I observed that abiotic disturbances significantly reduced soil microbial biomass, while changes in microbial biomass were non-significant following biotic disturbance events. Collectively, these findings suggest that reductions in soil microbial biomass and decomposition rates following abiotic disturbances are likely to slow the transfer of C from soils to the atmosphere and provide a negative feedback to rising atmospheric CO2 concentrations and global change.

As the threat of wildfires in the United States increases due to global warming, understanding their effects on the soil biological community becomes central to recovery efforts. Therefore, it is important to study microbial community dynamics in forest soils impacted by fires from the view of elucidating how the new state compares with the original state of the microbial community. For this study, wildfires were hypothesized to cause a shift in the microbial community structure with dominant microbes being those best capable of responding to changes in their environment caused by the perturbation. The objectives of this research were to examine the recovery of the forest soil microbial communities after a wildfire and to investigate the state of the communities more than two years post-fire. After a wildfire occurred in the New Jersey Pinelands in 2007, soil samples were collected from the organic and mineral layers of two severely burned sites and an unburned control site over the span of two years following the fire. Microbial community composition was evaluated by principal component analysis and multivariate analysis of variance of molecular fingerprint data for bacterial, archaeal, and fungal-specific amplicons from denaturing gradient gel electrophoresis. The bacterial communities in the samples collected from 2 and 5 months following the fire clustered separately from those collected 13 and 17 months post-fire in two-dimensional space, indicating that the soil bacterial community structure changed with time following the fire. Deeper evaluation of the bacterial, archaeal, and fungal community patterns revealed that even though there were common bands between the unburned and the severely burned samples, the community structure of the samples from the unburned site grouped separately from those of the severely burned sites collected 2, 13, and 25 months post-fire. Generally, the microbial community composition in the unburned samples did not change significantly over two years. These data support the hypothesis that the soil microbial community was selected by both the direct and indirect effects associated with the wildfire in the initial two years after the perturbation. Rather than return to the predisturbance state, the soil microbial communities may reflect an alternate state two years following the fire.

In this study of environmental risks in ten of the world's major cities, the contributors examine the hazard experiences of and analyze the future risks. They conclude that the natural disaster potential of the biggest cities is expanding at a pace which exceeds the rate of urbanization.

The population explosion that began in the 1960s has been accompanied by a decrease in the quality of the natural environment, e.g. pollution of the air, water and soil with essential and toxic trace elements. Numerous poisonings of people and animals with highly toxic anthropogenic Hg and Cd in the 20th century prompted the creation of the abiotic environment, mainly in developed countries. However, the system is insufficient for long-term exposure to low concentrations of various substances that are mainly ingested through food and water. This problem could be addressed by the monitoring of sentinels – organisms that accumulate trace elements and as such reflect the rate and degree of environmental pollution. Usually these are long-lived vertebrates – herbivorous, omnivorous and carnivorous birds and mammals, especially game species. This book describes the responses of the sentinels most commonly used in ecotoxicological studies to 17 trace elements.