Elevated air carbon dioxide concentrations increase dissolved carbon leaching from a cropland soil Jan Siemens • Andreas Pacholski • Katia Heiduk • Anette Giesemann • Ulrike Schulte • Rene ´ Dechow • Martin Kaupenjohann • Hans-Joachim Weigel Received: 19 April 2010 / Accepted: 14 February 2011 / Published online: 4 March 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Increasing leaching losses of carbon from soils due to accelerated weathering and increasing concentrations of dissolved carbon as a result of intensified soil respiration are suspected to provide a negative feedback on rising atmospheric CO 2 con- centrations. We tested this hypothesis by studying concentrations of dissolved carbon and groundwater recharge at the Braunschweig free air carbon dioxide enrichment (FACE) experiment under winter wheat and winter barley. Dissolved carbon concentrations under elevated atmospheric CO 2 and ambient condi- tions were rather similar and not consistently higher under FACE. An analysis of d 13 C signatures sug- gested that dissolved organic and inorganic carbon contained 9–29% (DOC) and 26–49% (DIC) of ‘‘new’’ carbon originating from CO 2 added to the FACE rings. Dissolved inorganic carbon additionally contained 15–42% of carbonate-derived C. A 15% reduction in evapotranspiration under elevated CO 2 increased groundwater recharge by 60 mm or 55%, which was the main driver for an observed 81% increase in dissolved carbon leaching from 2.7 to 4.9 g C m -2 year -1 at 90 cm depth. Our results suggest that future changes of dissolved carbon leaching losses will be mainly governed by changes in climate and groundwater recharge and to a lesser extent by increasing dissolved carbon concentrations. Keywords Free air carbon dioxide enrichment  Dissolved organic carbon  Dissolved inorganic carbon  Net biome productivity  Net ecosystem carbon balance  Carbon sequestration Introduction Photosynthetic carbon fixation by ecosystems drives the accumulation of organic matter and weathering of minerals in soils (e.g., Chadwick et al. 1994). The J. Siemens  M. Kaupenjohann Department of Soil Science, Technische Universita ¨t Berlin, Salzufer 12, 10587 Berlin, Germany J. Siemens (&) Institute of Crop Science and Resource Conservation, Soil Science, University of Bonn, Nussallee 13, 53115 Bonn, Germany e-mail: jan.siemens@uni-bonn.de A. Pacholski  K. Heiduk  A. Giesemann  R. Dechow  H.-J. Weigel Johann Heinrich von Thu ¨nen-Institut, Federal Research Institute for Rural Areas, Forestry and Fisheries, Bundesallee 50, 38116 Braunschweig, Germany Present Address: A. Pacholski Institute of Crop Science and Plant Breeding, Christian- Albrechts-Universita ¨t zu Kiel, Hermann-Rodewald-Str. 9, 24118 Kiel, Germany U. Schulte Institute of Geology, Mineralogy and Geophysics, Ruhr-Universita ¨t Bochum, Universita ¨tsstraße 150, 44801 Bochum, Germany 123 Biogeochemistry (2012) 108:135–148 DOI 10.1007/s10533-011-9584-0