Changes in the type and amount of plant inputs can occur gradually, as with succession, or rapidly, as with harvesting or wildfire. With global change it is anticipated that both gradual and immediate scenarios will occur at increasing frequency. Changes in vegetation inputs alter the quality and quantity of soil organic matter inputs, thus influencing the composition of soil microbial communities and the nutrient cycles they mediate. Understanding the relationship of soil organic matter inputs on soil microbial communities and nutrient cycles will be beneficial in predicting responses to changes in vegetation inputs. During the last 100-150 years, the vegetation of the Rio Grande Plains of the United States has been shifting from grasslands/savannas to woodlands as the result of encroachment of N2-fixing trees and their associated plant communities. The structure and diversity of soil microbial communities were examined under woody species and remnant grasslands. In addition, relationships between soil microbial communities and soil physical and chemical characteristics were explored. Soil microbial communities differed in soils under N2-fixing trees and associated vegetation compared to remnant grasslands. Differences in both fungal and bacterial communities were anticipated with vegetation shifts; however, only fungal communities correlated with vegetation, whereas bacterial communities were influenced by spatial heterogeneity. Soil microbial N cycling was investigated in long-term (>10 years) organic matter manipulations in an old-growth forest, dominated by large Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir). The objectives of this research were to: 1) determine if long-term organic matter manipulations in old-growth forests altered microbial N cycling, 2) determine the contribution of litter to N cycling, and 3) determine if litter quality (low C/N red alder and high C/N Douglas-fir) affected the contribution of litter-derived N to N transformations. Long-term organic matter manipulations were found to affect microbial C and N cycling, but to a lesser degree than anticipated. After 10 years of organic matter exclusions and additions, microbial communities in all treatments remained N limited, although N limitation was less severe in organic matter exclusion treatments. Adding leached litter to control and organic matter exclusion soils initially altered N processes but differences dissipated during a 151-day incubation. Litter quality had little impact on the N cycling and litter made modest contributions to N mineralization and nitrification. The exclusion of organic matter altered the functionality of the microbial community to access litter-derived N. Both the gradual establishment of woody clusters on grassland and abrupt manipulations of old-growth vegetation inputs elicited responses in microbial communities and N cycling. Although some responses were subtle, they nonetheless support the responsiveness and importance of microbial communities to soil processes. Understanding feedbacks among plant inputs, microbial communities and nutrient cycles will aid in predicting microbial, ecosystem, and global responses to vegetation changes.

Presenting the first continental-scale assessment of reactive nitrogen in the environment, this book sets the related environmental problems in context by providing a multidisciplinary introduction to the nitrogen cycle processes. Issues of upscaling from farm plot and city to national and continental scales are addressed in detail with emphasis on opportunities for better management at local to global levels. The five key societal threats posed by reactive nitrogen are assessed, providing a framework for joined-up management of the nitrogen cycle in Europe, including the first cost-benefit analysis for different reactive nitrogen forms and future scenarios. Incorporating comprehensive maps, a handy technical synopsis and a summary for policy makers, this landmark volume is an essential reference for academic researchers across a wide range of disciplines, as well as stakeholders and policy makers. It is also a valuable tool in communicating the key environmental issues and future challenges to the wider public.

History of abiontic soil ensyme research; Origin and range of enzymes in soil; kinetics and consecutive reactions of soil enzymes; Soil polysaccharidases: activity and agricultural importance; Urease activity in soils; Soil phosphatase and sulphatase; Interactions between agrochemicals and soil enzymes; Enzyme activity in soil: some theoretical and practical considerations; Methodology of soil enzyme measurement and extraction.

How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture. This dissertation consists of three studies that assess how variability in organic farms across an agricultural landscape may yield insights for improving N cycling and for evaluating novel indicators of N availability. Pulses of N are common in agricultural systems and often result in N losses if N is not quickly captured by plants or soil microbes. But understanding of how root behavioral responses and microbial N dynamics interact following soil N pulses remains limited, especially in soil under field conditions relevant to actual agroecosystem processes. The first study examined rhizosphere responses to a soil N pulse in an organic farm soil. A novel combination of molecular and 15N isotopic techniques was used to investigate the response of tomato (Solanum lycopersicum L.) roots and soil N cycling to a pulse of inorganic N in an undisturbed soil patch on an organic farm. Tomato roots rapidly responded to and exploited the N pulse via upregulation of key N metabolism genes that comprise the core physiological response of roots to patchy soil N availability. The transient root gene expression response underscored the sensitivity of root N uptake to local N availability. Strong root activity limited accumulation of soil nitrate (NO3−) despite high rates of gross nitrification and allowed roots to out-compete soil microbes for uptake of the inorganic N pulse, even on the short time scale of a few days. Root expression of genes such as cytosolic glutamine synthetase, a key gene in root N assimilation, could serve as a "plant's eye view" of N availability when plant-soil N cycling is rapid, complementing more typical measures of N availability like soil inorganic N pools and bioassays of N mineralization potential. Much of the research geared toward improving N cycling takes place at research stations with fixed management factors and limited variation in soil characteristics. Better understanding of how the plant-soil-microbe interactions that underpin N availability, potential for N loss, and yields vary across working farms would help reveal how to simultaneously achieve high provisioning (yields) and regulating (low potential for N loss) ecosystem services in heterogeneous landscapes. A landscape approach was thus used in the second and third studies to assess crop yields, plant-soil N cycling, root gene expression, and soil microbial community activity and composition over the course of a tomato growing season on working organic farms in Yolo County, California, USA. The 13 selected fields were representative of organic tomato production in the local landscape and spanned a three-fold range of soil carbon (C) and N but had similar soil types, texture, and pH. Yields ranged from 22.9 to 120.1 Mg ha−1 with a mean similar to the county average (86.1 Mg ha−1), which included mostly conventionally-grown tomatoes. Substantial variability in soil inorganic N concentrations, tomato N, and root gene expression indicated a range of possible tradeoffs between yields and potential for N losses across the fields. Soil enzyme activities reflected distinct metabolic capacity in each field, such that soil C-cycling enzyme potential activities increased with inorganic N availability while those of soil N-cycling enzymes increased with soil C availability. Compared to potential enzyme activity, there was less variation in soil microbial community composition, likely reflecting the history of high soil disturbance and low ecological complexity in this landscape. The variation in potential activity of soil enzymes across the organic fields thus may be due to high plasticity of the resident microbial community to environmental conditions. Those fields in the landscape that showed evidence of tightly-coupled plant-soil N cycling, a desirable scenario in which high crop yields are supported by adequate N availability but low potential for N loss, had the highest total and labile soil C and N and received diverse types of organic matter inputs with a range of N availability. In these fields, elevated expression of cytosolic glutamine synthetase in roots (as evaluated in the first study), confirmed that plant N assimilation was high even when soil inorganic N pools were low. The on-farm approach provided a wide range of farming practices and soil characteristics to reveal how microbially-derived ecosystem functions can be effectively manipulated to enhance nutrient cycling capacity. Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, and could overcome the uncertainty of managing N inputs accurately, especially when plant-soil N cycling is rapid.

Global biogeochemical cycles of carbon and nutrients are increasingly affected by human activities. So far, modeling has been central for our understanding of how this will affect ecosystem functioning and the biogeochemical cycling of carbon and nutrients. These models have been forced to adopt a reductive approach built on the flow of carbon and nutrients between pools that are difficult or even impossible to verify with empirical evidence. Furthermore, while some of these models include the response in physiology, ecology and biogeography of primary producers to environmental change, the microbial part of the ecosystem is generally poorly represented or lacking altogether. The principal pool of carbon and nutrients in soil is the organic matter. The turnover of this reservoir is governed by microorganisms that act as catalytic converters of environmental conditions into biogeochemical cycling of carbon and nutrients. The dependency of this conversion activity on individual environmental conditions such as pH, moisture and temperature has been frequently studied. On the contrary, only rarely have the microorganisms involved in carrying out the processes been identified, and one of the biggest challenges for advancing our understanding of biogeochemical processes is to identify the microorganisms carrying out a specific set of metabolic processes and how they partition their carbon and nutrient use. We also need to identify the factors governing these activities and if they result in feedback mechanisms that alter the growth, activity and interaction between primary producers and microorganisms. By determining how different groups of microorganisms respond to individual environmental conditions by allocating carbon and nutrients to production of biomass, CO2 and other products, a mechanistic as well as quantitative understanding of formation and decomposition of organic matter, and the production and consumption of greenhouse gases, can be achieved. In this Research Topic, supported by the Swedish research councils' programme "Biodiversity and Ecosystem Services in a Changing Landscape" (BECC), we intend to promote this alternative framework to address how cycling of carbon and nutrients will be altered in a changing environment from the first-principle mechanisms that drive them – namely the ecology, physiology and biogeography of microorganisms – and on up to emerging global biogeochemical patterns. This novel and unconventional approach has the potential to generate fresh insights that can open up new horizons and stimulate rapid conceptual development in our basic understanding of the regulating factors for global biogeochemical cycles. The vision for the research topic is to facilitate such progress by bringing together leading scientists as proponents of several disciplines. By bridging Microbial Ecology and Biogeochemistry, connecting microbial activities at the micro-scale to carbon fluxes at the ecosystem-scale, and linking above- and belowground ecosystem functioning, we can leap forward from the current understanding of the global biogeochemical cycles.

Several textbooks and edited volumes are currently available on general soil fertility but‚ to date‚ none have been dedicated to the study of “Sustainable Carbon and Nitrogen Cycling in Soil.” Yet this aspect is extremely important, considering the fact that the soil, as the ‘epidermis of the Earth’ (geodermis)‚ is a major component of the terrestrial biosphere. This book addresses virtually every aspect of C and N cycling, including: general concepts on the diversity of microorganisms and management practices for soil, the function of soil’s structure-function-ecosystem, the evolving role of C and N, cutting-edge methods used in soil microbial ecological studies, rhizosphere microflora, the role of organic matter (OM) in agricultural productivity, C and N transformation in soil, biological nitrogen fixation (BNF) and its genetics, plant-growth-promoting rhizobacteria (PGPRs), PGPRs and their role in sustainable agriculture, organic agriculture, etc. The book’s main objectives are: (1) to explain in detail the role of C and N cycling in sustaining agricultural productivity and its importance to sustainable soil management; (2) to show readers how to restore soil health with C and N; and (3) to help them understand the matching of C and N cycling rules from a climatic perspective. Given its scope, the book offers a valuable resource for educators, researchers, and policymakers, as well as undergraduate and graduate students of soil science, soil microbiology, agronomy, ecology, and the environmental sciences. Gathering cutting-edge contributions from internationally respected researchers, it offers authoritative content on a broad range of topics, which is supplemented by a wealth of data, tables, figures, and photographs. Moreover, it provides a roadmap for sustainable approaches to food and nutritional security, and to soil sustainability in agricultural systems, based on C and N cycling in soil systems.

Microbial Biomass informs readers of the ongoing global revolution in understanding soil and ecosystem microbial processes. The first paper on the subject was written by David Jenkinson in 1966, and here new insights and expansions are given on the fascinating world of soil microbial processes. In terms of contemporary issues, it also serves to support urgent efforts to sustainably manage land to feed a growing world population without compromising the environment. It presents new methods of investigation which are leading to more sustainable management of ecosystems, and improved understanding of ecosystem changes in an increasingly warmer world.The book approaches the topic by looking at the emergence of our understanding of soil biological processes, and begins by tracing the conception and first measurement of soil microbial biomass. Following this, changes in ecosystems, and in natural ecosystem processes are discussed in relation to land management issues and global change. Microbial biomass and its diversity are recognized as key factors in finding solutions for more sustainable land and ecosystem management, aided by new molecular and other tools. Information from the use of these tools is now being incorporated into emerging microbial-explicit predictive models, to help us study changes in earth system processes.Perfect for use in research and practice, this book is written for undergraduate and graduate students, researchers and professionals of agronomy, chemistry, geology, physical geography, ecology, biology, microbiology, silviculture and soil science.