Laughing Gas, Forests, Coastal Regions and Global Warming

Forest ecosystems may produce large volumes of nitrous oxide (N2O), an important greenhouse gas, which affects the atmosphere's chemical and radiative properties. Yet, our understanding of controls on forest N2O emissions is insufficient. This study investigates the quantitative and qualitative relationships between nitrogen-cycling and N2O production in European forests.

The authors conclude that changes in forest composition in response to land use activities and global change may have serious implications for regional budgets of greenhouse gases. It also became clear that accelerated nitrogen inputs predicted for forest ecosystems in Europe may lead to increased greenhouse gas emissions from forest ecosystems.

Read article: http://www.biogeosciences.net/3/135/2006/bg-3-135-2006.html

Bacterial carbon sources in coastal sediments: a cross-system analysis based on stable isotope data of biomarkers.

Coastal ecosystems are among the most productive regions in the world ocean. Because of the ample nutrient supplies, the coastal zone accounts for about 20% of oceanic primary production — despite its small geographic extent. Local organic producers span from phytoplankton to bottom-dwelling algae to seagrasses and mangroves. Because of the high rates of sediment accumulation, among other factors, a comparatively large percentage of this new organic matter survives early decay and is buried into the geologic record. Coastal regions also receive large inputs of organic material reworked and transported from surrounding regions by strong currents, including contributions from rivers that drain adjacent land areas. Through the combined effects of high production, large inputs of reworked material, and efficient sequestration, a vast majority of the world’s organic carbon burial occurs in these marginal marine settings.

As the dominant site of oceanic organic carbon burial, the coastal zone factors prominently in most models for short- and long-term carbon cycling and, correspondingly, in scientists’ estimates for CO2 variation in the atmosphere on a variety of time scales. In this paper, Bouillon and Boschker explore this complex organic reservoir through carbon isotope analysis of the many constituents, including large plant fragments and lipid biomarkers that are chemically extracted from the sediments and fingerprint bacterial sources.

Using this approach the authors explored which of the organic components bacteria most easily degrade and thus which have the potential for burial and removal from at least the short-term carbon cycle. Importantly, the authors compared the carbon isotope properties of bacterial biomarkers from a wide range of coastal settings and concluded that the microbes are feeding on a diverse assortment of organic constituents. In fact, at most sites where organic matter is readily available, bacteria show little selectivity in the compounds they decompose.

In light of the previous consensus that such materials should show widely varying biodegradability, this result will certainly raise questions, fuel future work, and ultimately refine our understanding of how carbon flows through its global biogeochemical cycle and impacts the composition of the atmosphere.

Read article: http://www.biogeosciences.net/3/175/2006/bg-3-175-2006.html