Gases with a mixing ratio of less than one percent in the lower atmosphere (i.e. the troposphere) are considered as trace gases. Numerous of these trace gases originate from biological processes in marine and terrestrial ecosystems. These gases are of relevance for the climate as they contribute to global warming or to the troposphere’s chemical reactive system that builds the ozone layer or they impact on the stability of aerosols, greenhouse, and pollutant gases. These reactive trace gases include methane, a multitude of volatile organic compounds of biogenic origin (bVOCs) and inorganic gases such as nitrogen oxides or ozone. The regulatory function of microorganisms for trace gas cycling has been intensively studied for the greenhouse gases nitrous oxide and methane, but is less well understood for microorganisms that metabolize molecular hydrogen, carbon monoxide, or bVOCs. The studies compiled this Research Topic reflect this very well. While a number of articles focus on nitrous oxide and methane or carbon monoxide oxidation, only a few articles address conversion processes of further bVOCs. The Research Topic is complemented by three review articles about the consumption of methane and monoterpenes, as well as the role of the phyllosphere as a particular habitat for trace gas-consuming microorganisms, and point out future research directions in the field. The presented scientific work illustrates that the field of microbial regulation of trace glas fluxes is still in its infancy when one broadens the view on gases beyond methane and nitrous oxide. However, there is a societal need to better predict global dynamics of trace gases that impact on the functionality and warming of the troposphere. Upcoming modelling approaches will need further information on process rates, features and distribution of the driving microorganisms to fullfill this demanding task.

Gases with a mixing ratio of less than one percent in the lower atmosphere (i.e. the troposphere) are considered as trace gases. Numerous of these trace gases originate from biological processes in marine and terrestrial ecosystems. These gases are of relevance for the climate as they contribute to global warming or to the troposphere's chemical reactive system that builds the ozone layer or they impact on the stability of aerosols, greenhouse, and pollutant gases. These reactive trace gases include methane, a multitude of volatile organic compounds of biogenic origin (bVOCs) and inorganic gases such as nitrogen oxides or ozone. The regulatory function of microorganisms for trace gas cycling has been intensively studied for the greenhouse gases nitrous oxide and methane, but is less well understood for microorganisms that metabolize molecular hydrogen, carbon monoxide, or bVOCs. The studies compiled in this Research Topic reflect this very well. While a number of articles focus on nitrous oxide and methane or carbon monoxide oxidation, only a few articles address conversion processes of further bVOCs. The Research Topic is complemented by three review articles about the consumption of methane and monoterpenes, as well as the role of the phyllosphere as a particular habitat for trace gas-consuming microorganisms, and point out future research directions in the field. The presented scientific work illustrates that the field of microbial regulation of trace glas fluxes is still in its infancy when one broadens the view on gases beyond methane and nitrous oxide. However, there is a societal need to better predict global dynamics of trace gases that impact on the functionality and warming of the troposphere. Upcoming modelling approaches will need further information on process rates, features and distribution of the driving microorganisms to fulfill this demanding task.

The chapters making up this volume are based on the presentations given by their authors at the NATO Advanced Research Workshop (ARW) , also entitled "The Microbiology of Atmospheric Trace Gases: Sources, Sinks and Global Change Processes", held between 13-18 May 1995 at II Ciocco, Castelvecchio Pascoli, Tuscany, Italy. Four reports of Working Group discussions on aspects of trace gas microbiology and climate change are also included in the volume, prepared by rapporteurs designated at the ARW. All the papers here presented have been subjected to peer review by at least two referees and corrections and amendments made where necessary before their acceptance for pUblication in this volume. The ARW was set up to address a wide range of issues relating to atmospheric trace gas microbiology and the organizing group was aware of the burgeoning of studies on gas metabolism and on global effects of atmospheric trace gases over the past two decades. This research effort has led to a number of specialist and generalist meetings including the triennial series of symposia on the metabolism of one-carbon compounds, colloquia concerned with dimethyl sulfide and its precursor, DMSP, through to the Intergovernmental Panels on Climate Change, which have addressed the impact of increasing levels of atmospheric carbon dioxide, methane, nitrous oxide and chlorofluorocarbons on global climate. Over recent years methane and nitrous oxide showed rates of increase in the atmosphere of 40-48 and 3-4. 5 Tg/year, respectively.

This volume reviews current data on the relationship between microbial processes and the synthesis and degradation of methane, nitrogen oxides and halomethanes in the environment.

Microbiological basic of NO and N2O production and consumption in soil; Factors controlling NOx emissions from soils; Control of methane production in terrestrial ecosystems; Biological sinks of methane; What regulates production and consumption of trace gases in ecosystems: biology or physicochemistry?; Regional extrapolation of trace gas flux based on soil and ecosystems; Regional extrapolation: Vegetation-atmosphere approach; Global-scale extrapolation: a critical assessment; Aircraft-based measurements of trace gas fluxes; Extrapolation of flux measurements to regional and global scales; Chamber and isotop techniques; Micrometeorological techniques for the measurement of trace gas exchange; Methane flux measurements: methods and results; Fluxes of NOx abovesoil and vegetation; What are the relative roles of biological production, micrometeorology, and photochemistry in controlling the flux of trace gases between terrestrial ecosystems and the atmosphere?; Atmospheric deposition and nutrient cycling; Global climate and trace gas composition: from atmospheric history to the century; Experimental design for studying atmosphere interactions; Trace gas exchange and phsical climate: Critical interactions; Research priorities for studies on trace gas exchange.

Certain trace gases in the atmosphere are able to absorb electromagnetic energy from the reflection of solar radiation from the Earth's surface. These gases have been increasing steadily and there is concern that they will change global climatic conditions by warming the atmosphere--the so-called ``greenhouse effect.'' Many of these gases originate from biological systems. The Biogeochemistry of Global Change discusses the role of radiative trace gases in this process. The disciplines covered in the book include microbiology, geochemistry, atmospheric chemistry, plant physiology, oceanography and limnology, and soil science. This diversity allows for cross-fertilization, achieving a better understanding of the complex mechanisms for biological and chemical formation, the destruction of trace gases, and the manipulation of ecosystems. Some of the topics covered include: biological mechanisms of formation and destruction of various ``greenhouse'' gases (such as methane, nitrous oxide, carbon dioxide, dimethylsulfide, and chlorofluorocarbons); the outward and consumptive flux of trace gases from marine and terrestrial systems (including anthropogenic sources); global trace gas modeling studies; the atmospheric physical and chemical reactions of trace gases; and the environmental significance of various trace gases in ancient and current atmospheres. The Biogeochemistry of Global Change provides both reviews and primary source material for active researchers in this field and for microbiologists and atmospheric chemists.