Influence Of Elevated Carbon Dioxide On Soil Atmosphere Exchange Of Methane And Nitrous Oxide In A Coniferous Forest

The Carbon Balance of Forest Biomes provides an informed synthesis on the current status of forests and their future potential for carbon sequestration. This volume is timely, since convincing models which scale from local to regional carbon fluxes are needed to support these international agreements, whilst criticisms have been levelled at existing empirical approaches. One key question is to determine how well eddy-flux measurements at the stand-level represent regional-scale processes. This may be related to specific management practices (age, plantation, fertilisation) or simple bias in choosing representative sites (ease of access, roughness, proximity to physical barriers). The ecology and regeneration state of temperate, tropical and boreal forests under current climatic conditions are discussed, together with partitioning of photosynthetic and respiratory fluxes from soils and vegetation. The volume considers how to integrate contrasting methodologies, and the latest approaches for scaling from stand to the planetary boundary layer.

The Aspen free-air carbon dioxide (CO2) enrichment (FACE) experiment tested how three developing forest communities responded to elevated concentrations of CO2 and/or tropospheric ozone (O3). Throughout the 11-year experiment, elevated CO2 increased aboveground productivity, whereas the initial negative effects of elevated O3 on aboveground productivity became insignificant over time. During the first 2 years, fine root biomass and soil respiration responded positively to elevated CO2 and negatively to elevated O3. However, after 5 years, O3 effects on fine root biomass were weakly negative or positive and effects on soil respiration were positive. Despite altering litter inputs, neither elevated O3 nor elevated CO2 affected overall soil C storage at the end of the experiment, consistent with observations that elevated CO2 increased and elevated O3 tended to decrease the activity of litter-degrading extracellular enzymes. Overall, our understanding of belowground processes is still insufficient to predict how ecosystems will respond to global change.

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.

Nitrogen transformation processes; The nitrogen cycle in different systems; Advances in nitrogen methodology; 15N recovery techniques in the field.

This book provides a review, written by international forest scientists, of what is known about the impact of elevated CO2 and other greenhouse gases, on forest ecosystems.

Forest ecosystems are often disturbed by agents such as harvesting, fire, wind, insects and diseases, and acid deposition, with differing intensities and frequencies. Such disturbances can markedly affect the amount, form, and stability of soil organic carbon in, and the emission of greenhouse gases, including CO2, CH4, and N2O from, forest ecosystems. It is vitally important that we improve our understanding of the impact of different disturbance regimes on forest soil carbon dynamics and greenhouse gas emissions to guide our future research, forest management practices, and policy development. This Special Issue provides an important update on the disturbance effects on soil carbon and greenhouse gas emissions in forest ecosystems in different climate regions.

Cycles, water, carbon.