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Abstract: Studies in tropical and temperate regions and in the laboratory have shown that the addition of biochar into agricultural soils has potential to mitigate climate change by increasing crop yield per area, decreasing nitrous oxide (N2O) emissions and increasing soil carbon (C) storage. The impacts of biochar on plant productivity and soil processes are, however, highly variable depending on the properties of the biochar and the soil, plant species and environmental conditions. We studied the effects of biochar addition on soil moisture, yield of Phleum pratense (timothy), respiration and N2O emissions in mesocosms with a bare mineral soil or P. pratense stand. Biochar was made from spruce chips under rather low temperatures (400–450 °C) and was mixed into the whole soil layer of 45 cm during the preparation of the mesocosms. The mesocosms were fertilized with ammonium nitrate (NH4NO3;100 kg N ha−1) at the beginning of the experiment and after each harvest. Air temperature was maintained at 20 °C during the daytime and at 15 °C at night. Soil temperature was kept at a constant 15 °C. Biochar increased soil moisture increasing soil respiration and N2O emissions in the bare soil mesocosms, and yield, nitrogen (N) content and N uptake in P. pratense decreasing N2O efflux in the vegetated mesocosms under dry conditions (surface soil moisture 20–30%). Under wet conditions (surface soil moisture 40–50%), N2O emissions increased in the vegetated mesocosms simultaneously with the decreased N uptake in P. pratense harvest. Biochar could thus benefit agriculture, especially during the dry periods of the growing season, but might also increase N2O emissions. Biochar affected N2O efflux indirectly via soil moisture and plant N uptake. [Copyright &y& Elsevier]

This study was conducted to estimate annual CH4 efflux from wetlands and watercourses in Europe and some adjacent areas. Wet ecosystems were divided into seven categories: ombrotrophic mires, minerotrophic mires, freshwater marshes, saltwater marshes, small lakes, large lakes and rivers. The geographical distribution and total area coverage for each of these respective ecosystems were taken from CORINE 2000, Global Land Cover 2000 [JRC, 2003. Harmonisation, mosaicing and production of the Global Land Cover 2000 database (Beta Version). EUR 20849 EN, Joint Research Center, Ispra, Italy] and ESRI 2003 databases. CH4 release factors were obtained from an extensive overview of published literature. Less than 3% of the study area of 22,560,000km2 consisted of wetlands and watercourses. Large lakes (40%), minerotrophic mires (24%) and ombrotrophic mires (20%) covered almost 85% of the total area of wetlands and watercourses. The total CH4 release from European wetlands and watercourses was estimated to be 5.2Tga−1. CH4 release from minerotrophic mires (48%), large lakes (24%), and ombrotrophic mires (12%) composed most of the total CH4 efflux. High variation in the rate of CH4 release within the main ecosystem types, small number of studies in some ecosystems and ecologically inadequate land-cover classification are the main reasons for the uncertainties of the estimate. A better estimation of European CH4 effluxes from natural sources, now and future, would require: a much more detailed and ecologically relevant mapping of the area of different types of wetlands and watercourses, and long-term measurements of CH4 fluxes and their controlling environmental factors in poorly studied types of wetlands and watercourses. Finally, the data could be used for dynamic modelling of CH4 fluxes in the current and changing environmental conditions. [Copyright &y& Elsevier]