Understanding the effects climate change will have on the structure and function of global ecosystems is a pressing ecological and social issue. Global change driven changes in atmospheric warming and precipitation régimes have begun to alter the distribution of plants and animals in, as well as the function of, ecosystems. Using two large-scale climate change manipulations, I assessed the effect of changing precipitation and temperature regimes on soil microbial community structure and function. Soil microbial communities regulate decomposition and nutrient cycling rates in ecosystems, thus understanding their response to climatic changes will enable scientists to better predict carbon feedbacks to the atmosphere as well as functional shifts within ecosystems. My first two chapters took advantage of a large-scale precipitation manipulation in a semi-arid woodland. My first chapter aimed to understand how changing precipitation amounts altered the structure and abundance of soil bacteria and fungi; while my second chapter measured how changing precipitation altered soil nitrogen cycling. Overall, I found that soil microbial community composition and function were responsive to changes in precipitation, but these responses were contingent upon seasonal variability in precipitation and the aboveground plant community. My final experiment examined how changing temperature altered soil microbial community structure and function in two temperate forests. Using a large scale warming experiment at two locations, I examined how changes in temperature altered microbial composition, abundance, potential enzyme activity, and decomposition. I found that the effects of warming were contingent upon location; microbial community composition responded to alterations in soil temperature and soil moisture at the warmer site, but not at the cooler site. Unexpectedly, the change in microbial community composition did not result in changes in the rate of decomposition. I conclude that the soil is relatively buffered from atmospheric warming thus changes in microbial community structure and function may take longer than a few years to develop. Taken together, my research demonstrates that understanding the effects of climate change on microbial community structure and function is complex and contingent upon the background abiotic and biotic variability within an ecosystem.

Microbes in Land Use Change Management details the various roles of microbial resources in management of land uses and how the microbes can be used for the source of income due to their cultivation for the purpose of biomass and bioenergy production. Using various techniques, the disturbed and marginal lands may also be restored eco-friendly in present era to fulfil the feeding needs of mankind around the globe. Microbes in Land Use Change Management provides standard and up to date information towards the land use change management using various microbial technologies to enhance the productivity of agriculture. Needless to say that Microbes in Land Use Change Management also considers the areas including generation of alternative energy sources, restoration of degraded and marginal lands, mitigation of global warming gases and next generation -omics technique etc. Land use change affects environment conditions and soil microbial community. Microbial population and its species diversity have influence in maintaining ecosystem balance. The study of changes of microbial population provides an idea about the variation occurring in a specific area and possibilities of restoration. Meant for a multidisciplinary audience Microbes in Land Use Change Management shows the need of next-generation omics technologies to explore microbial diversity. Describes the role of microbes in generation of alternative source of energy Gives recent information related to various microbial technology and their diversified applications Provides thorough insight in the problems related to landscape dynamics, restoration of soil, reclamation of lands mitigation of global warming gases etc. eco-friendly way using versatility of microbes Includes microbial tools and technology in reclamation of degraded, disturbed and marginal lands, mitigation of global warming gases

Tropical ecosystems are different in important ways from those of temperate regions. They are a major reservoir of plant and animal biodiversity and play important roles in global climate regulation and biogeochemical cycling. They are also under great threat due to the conversion of tropical ecosystems to other uses. Thus, in the context of global change, it is crucial to understand how environmental factors, biogeographic patterns, and land use changes interact to influence the structure and function of microbial communities in these ecosystems. The contributions to this Research Topic showcase the current knowledge regarding microbial ecology in tropical ecosystems, identify many challenges and questions that remain to be addressed and open up new horizons in our understanding of the environmental and anthropological factors controlling microbial communities in these important ecosystems.

In this study, microorganisms are vital in mediating the earth's biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: 'When do we need to understand microbial community structure to accurately predict function?' We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.

Dams or barriers are among the most significant anthropogenic threats to global freshwater ecosystems, although they provide invaluable services for shipping, hydropower generation, flood protection, and storage of drinking and irrigation water. River fragmentations due to dams and barriers lead the aquatic landscape into isolated river sections, resulting in hydromorphological discontinuities along longitudinal or lateral gradients. Fragmented river habitats are unstable. They experience uncertain disturbances in both time and space with random and complex hydrological and environmental processes, such as water flow, particulate matter sedimentation, reservoir regulation, and terrestrial input. The diversity, composition, functionality, and activity of microbial communities are important indicators of river ecosystem functions and services. Yet, river fragmentations are likely to disrupt and reconstruct microbial communities, redirecting the patterns of biogeochemical cycles of biogenic elements. Methodology, such as mathematical models, is still limited to describing and elucidating microbial processes under changing hydrological environments in the fragmented rivers. Thus, how do the riverine microbial communities and ecosystem functions respond to the fragmentation in rivers? This Research Topic represents a collective focus on microbial ecology, functional diversity, and new microbial modeling in fragmented rivers. We wish to present new findings in community assembly mechanisms, biotic interactions, functional diversity, and ecosystem functioning responses to the river fragmentations. New perspectives will also provide us with deep insights into the ecological effects of river fragmentation. This Research Topic aims to present the original research articles and reviews to provide new findings on microbial diversity and ecosystem functioning in fragmented rivers worldwide. We welcome original research, reviews, mini-reviews, opinions, methods, hypotheses and theories, and perspectives. The directions include but are not limited to the following aspects: - The continuum of the microbial community in responses to dams or barriers. - Novel microbial community assembly mechanisms, functional traits, and biotic interactions in fragmented rivers at local, regional, and global scales. - Functional genes, functional groups, and functional diversity in driving biogenic element cycles. - Mathematical modeling in aquatic microbial ecology.

Understanding the link between microbial diversity and ecosystem processes is a fundamental goal of microbial ecologists, yet we still have a rudimentary knowledge of how changes in diversity affect nutrient cycling and energy transfer in ecosystems. Due to the complexity of the problem, many published studies on this topic have been conducted in artificial or manipulated systems. Although researchers have begun to expose some possible mechanisms using these approaches, most have not yet been able to produce conclusive results that relate directly to natural systems. The few studies that have explored the link between diversity and activity in natural systems have typically focused on specific nutrient cycles or processes, such as nitrification, denitrification, and organic carbon degradation pathways, and the microbes that mediate them. What we have learned from these studies is that there are often strong associations between the physical and chemical features of the environment, the composition of the microbial communities, and their activities, but the rules that govern these associations have not been fully elucidated. These earlier studies of microbial diversity and processes in natural systems provide a framework for additional studies to broaden our understanding of the role of microbial diversity in ecosystem function. The problem is complex, but with recent advances in sequencing technology, -omics, and in-situ measurements of ecosystem processes and their applications to microbial communities, making direct connections between ecosystem function and microbial diversity seems more tractable than ever.

Beginning with the germ theory of disease in the 19th century and extending through most of the 20th century, microbes were believed to live their lives as solitary, unicellular, disease-causing organisms . This perception stemmed from the focus of most investigators on organisms that could be grown in the laboratory as cellular monocultures, often dispersed in liquid, and under ambient conditions of temperature, lighting, and humidity. Most such inquiries were designed to identify microbial pathogens by satisfying Koch's postulates.3 This pathogen-centric approach to the study of microorganisms produced a metaphorical "war" against these microbial invaders waged with antibiotic therapies, while simultaneously obscuring the dynamic relationships that exist among and between host organisms and their associated microorganisms-only a tiny fraction of which act as pathogens. Despite their obvious importance, very little is actually known about the processes and factors that influence the assembly, function, and stability of microbial communities. Gaining this knowledge will require a seismic shift away from the study of individual microbes in isolation to inquiries into the nature of diverse and often complex microbial communities, the forces that shape them, and their relationships with other communities and organisms, including their multicellular hosts. On March 6 and 7, 2012, the Institute of Medicine's (IOM's) Forum on Microbial Threats hosted a public workshop to explore the emerging science of the "social biology" of microbial communities. Workshop presentations and discussions embraced a wide spectrum of topics, experimental systems, and theoretical perspectives representative of the current, multifaceted exploration of the microbial frontier. Participants discussed ecological, evolutionary, and genetic factors contributing to the assembly, function, and stability of microbial communities; how microbial communities adapt and respond to environmental stimuli; theoretical and experimental approaches to advance this nascent field; and potential applications of knowledge gained from the study of microbial communities for the improvement of human, animal, plant, and ecosystem health and toward a deeper understanding of microbial diversity and evolution. The Social Biology of Microbial Communities: Workshop Summary further explains the happenings of the workshop.