Soil organic matter (SOM) is the terrestrial biosphere's largest pool of organic carbon (C) and is an integral part of C cycling globally. Soil organic matter composition typically can be traced directly back to the type of detrital inputs; however, the stabilization of SOM results as a combination of chemical recalcitrance, protection from microbial decomposition within soil structure, and organo-mineral interactions. A long-term manipulative field experiment, the Detrital Input and Removal Treatment (DIRT) Project, was established to examine effects of altering detrital inputs (above- vs. below-ground source, C and nitrogen (N) quantity, and chemical quality) on the stabilization and retention of SOM. Surface mineral soil was collected from two DIRT sites, Bousson (a deciduous site in western Pennsylvania) and H.J. Andrews (a coniferous site in the Oregon Cascade Mountains), to examine the influence of altering detrital inputs on decomposability and mean residence time of soil organic matter and different organic matter fractions. Soil organic matter was physically separated into light fraction (LF) and heavy fraction (HF) organic matter, by density fractionation in 1.6 g mL−1 sodium polytungstate (SPT). Density fractionation in SPT resulted in the mobilization and loss of ~25% of total soil organic C and N during the physical separation and rinsing of fractions during recovery, which was also the most easily decomposed organic matter present in the bulk soil. At H.J. Andrews, this mobilized organic matter had a short mean residence time (MRT), indicating that it originated from fresh detrital inputs. In contrast, at Bousson, the organic matter mobilized had a long MRT, indicating that it originated from organic matter that had already been stabilized in the soil. Mean residence times of LF from Bousson varied widely, ~3 y from doubled litter and control plots and 78-185 y for litter removal plots, while MRT of HF was ~250 y and has not yet been affected by litter manipulations. Results from long term incubation of LF and HF material supported these estimates; respiration was greatest from LF of doubled litter and control plots and least from HF of litter removal plots. In contrast, MRT estimated for LF and HF organic matter from H.J. Andrews were similar to each other (~100 y) and were not affected by litter manipulation. These estimates were also supported by the incubation results; there was not a difference in cumulative respiration between detrital treatments or density fractions. The results from the coniferous site may be due to a legacy of historically large inputs of coarse woody debris on the LF and it may be decades before the signal of detrital manipulations can be measured. Alternatively, these highly andic soils may be accumulating C rapidly, yielding young HF ages and C that does not differ substantially in lability from coniferous litter-derived LF. The DIRT Project was intended to follow changes in soil organic matter over decades to centuries. As expected, manipulation of detrital inputs has influenced the lability and mean residence time of the light fraction before the heavy fraction organic matter; however, it will be on much more lengthy time scales that clear differences in organic matter stabilization in response to the alteration of detrital inputs will emerge. Soil CO2 efflux is a compilation of CO2 from many sources, including root respiration and the decomposition of different organic matter fractions, roots, and exudates. If the sources of CO2 have different isotopic signatures, the isotope analysis of CO2 efflux may reveal the dominant sources within the soil profile. In a short incubation experiment of density fractions from both sites, respired CO2 reflected the isotopic signature of the organic matter fraction after 30 days, but was more enriched in 13C. Initially CO2 was isotopically depleted in 13C relative to the organic matter fraction and the period of depletion related to the amount of easily degraded organic matter present at H.J. Andrews only.

Forest soil characteristics are not only unique but their interpretation also differs from cropland soils. Just as there are diverse forest types, there are many soil variants that need different management. Today, forest plantations are being intensively managed for profitable timber, pulpwood and energy production. Site selection, species selection, site productivity evaluation, silvicultural treatments, and soil amendments need crucial soil information. This book provides a comprehensive overview of the physical, chemical and biological properties of forest soils and their implications on forest vegetation. Topics discussed include: major forest types of the world and their associated soils; forest biomass and nutrient dynamics; organic matter turnover and nutrient recycling; forest soil disturbance; forest soil and climate change; and forest soil management and silvicultural treatments.

Litter Decomposition describes one of the most important processes in the biosphere - the decay of organic matter. It focuses on the decomposition process of foliar litter in the terrestrial systems of boreal and temperate forests due to the greater amount of data from those biomes. The availability of several long-term studies from these forest types allows a more in-depth approach to the later stages of decomposition and humus formation. Differences between the decay of woody matter and foliar litter is discussed in detail and a different pattern for decomposition is introduced. While teachers and students in more general subjects will find the most basic information on decomposition processes in this book, scientists and graduate students working on decomposition processes will be entirely satisfied with the more detailed information and the overview of the latest publications on the topic as well as the methodological chapter where practical information on methods useful in decomposition studies can be found. Abundant data sets will serve as an excellent aid in teaching process and will be also of interest to researchers specializing in this field as no thorough database exists at the moment. Provides over 60 tables and 90 figures Offers a conceptual 3-step model describing the different steps of the decomposition process, demonstrating changes in the organic-chemical structure and nutrient contents Includes a synthesis of the current state of knowledge on foliar litter decomposition in natural systems Integrates more traditional knowledge on organic matter decomposition with current problems of environmental pollution, global change, etc. Details contemporary knowledge on organic matter decomposition

Carbon stored in soils represents the largest terrestrial carbon pool and factors affecting this will be vital in the understanding of future atmospheric CO2 concentrations. This book provides an integrated view on measuring and modeling soil carbon dynamics. Based on a broad range of in-depth contributions by leading scientists it gives an overview of current research concepts, developments and outlooks and introduces cutting-edge methodologies, ranging from questions of appropriate measurement design to the potential application of stable isotopes and molecular tools. It includes a standardised soil CO2 efflux protocol, aimed at data consistency and inter-site comparability and thus underpins a regional and global understanding of soil carbon dynamics. This book provides an important reference work for students and scientists interested in many aspects of soil ecology and biogeochemical cycles, policy makers, carbon traders and others concerned with the global carbon cycle.

This open access book synthesizes leading-edge science and management information about forest and rangeland soils of the United States. It offers ways to better understand changing conditions and their impacts on soils, and explores directions that positively affect the future of forest and rangeland soil health. This book outlines soil processes and identifies the research needed to manage forest and rangeland soils in the United States. Chapters give an overview of the state of forest and rangeland soils research in the Nation, including multi-decadal programs (chapter 1), then summarizes various human-caused and natural impacts and their effects on soil carbon, hydrology, biogeochemistry, and biological diversity (chapters 2–5). Other chapters look at the effects of changing conditions on forest soils in wetland and urban settings (chapters 6–7). Impacts include: climate change, severe wildfires, invasive species, pests and diseases, pollution, and land use change. Chapter 8 considers approaches to maintaining or regaining forest and rangeland soil health in the face of these varied impacts. Mapping, monitoring, and data sharing are discussed in chapter 9 as ways to leverage scientific and human resources to address soil health at scales from the landscape to the individual parcel (monitoring networks, data sharing Web sites, and educational soils-centered programs are tabulated in appendix B). Chapter 10 highlights opportunities for deepening our understanding of soils and for sustaining long-term ecosystem health and appendix C summarizes research needs. Nine regional summaries (appendix A) offer a more detailed look at forest and rangeland soils in the United States and its Affiliates.