Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 3 2010 10.5194/bg-7-1031-2010 http://www.biogeosciences.net/7/1031/2010/ http://www.biogeosciences.net/7/1031/2010/bg-7-1031-2010.html http://www.biogeosciences.net/7/1031/2010/bg-7-1031-2010.pdf 1031 1041 2010-03-17 Summer drought reduces total and litter-derived soil CO₂ effluxes in temperate grassland – clues from a ¹³C litter addition experiment O. Joos F. Hagedorn hagedorn@wsl.ch A. Heim A. K. Gilgen M. W. I. Schmidt R. T. W. Siegwolf N. Buchmann University of Zurich, Department of Geography, Zurich, Switzerland Swiss Federal Institute for Forest, Snow and Landscape Research, WSL Birmensdorf, Switzerland ETH Zurich, Institute of Plant Sciences, Switzerland Paul Scherrer Institute, PSI Villigen, Switzerland University of Bern, Institute of Plant Sciences, Switzerland Current climate change models predict significant changes in rainfall patterns across Europe. To explore the effect of drought on soil CO₂ efflux (<i>F</i>_Soil) and on the contribution of litter to <i>F</i>_Soil we used rain shelters to simulate a summer drought (May to July 2007) in an intensively managed grassland in Switzerland by reducing annual precipitation by around 30% similar to the hot and dry year 2003 in Central Europe. We added ¹³C-depleted as well as unlabelled grass/clover litter to quantify the litter-derived CO₂ efflux (<i>F</i>_Litter). Soil CO₂ efflux and the ¹³C/¹²C isotope ratio (&delta;¹³C) of the respired CO₂ after litter addition were measured during the growing season 2007. Drought significantly decreased <i>F</i>_Soil in our litter addition experiment by 59% and <i>F</i>_Litter by 81% during the drought period itself (May to July), indicating that drought had a stronger effect on the CO₂ release from litter than on the belowground-derived CO₂ efflux (<i>F</i>_BG, i.e. soil organic matter (SOM) and root respiration). Despite large bursts in respired CO₂ induced by the rewetting after prolonged drought, drought also reduced <i>F</i>_Soil and <i>F</i>_Litter during the entire ¹³C measurement period (April to October) by 26% and 37%, respectively. Overall, our findings show that drought decreased <i>F</i>_Soil and altered its seasonality and its sources. Thus, the C balance of temperate grassland soils respond sensitively to changes in precipitation, a factor that needs to be considered in regional models predicting the impact of climate change on ecosystems C balance. % vor jede Referenz Amundson, R.: The carbon budget in soils, Annu. Rev. Earth Planet. Sci., 29, 535–562, 2001. 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