ORIGINAL PAPER Arthur Geßler Klaus Jung Rainer Gasche Hans Papen Anita Heidenfelder Eric Bo¨rner Berthold Metzler Sabine Augustin Ernst Hildebrand Heinz Rennenberg Climate and forest management influence nitrogen balance of European beech forests: microbial N transformations and inorganic N net uptake capacity of mycorrhizal roots Received: 29 July 2004 / Accepted: 8 November 2004 / Published online: 13 May 2005 Ó Springer-Verlag 2005 Abstract The effects of local climate and silvicultural treatment on the inorganic N availability, net N uptake capacity of mycorrhizal beech roots and microbial N conversion were assessed in order to characterise changes in the partitioning of inorganic N between adult beech and soil microorganisms. Fine root dynamics, inorganic N in the soil solution and in soil extracts, nitrate and ammonium uptake kinetics of beech as well as gross ammonification, nitrification and denitrification rates were determined in a beech stand consisting of paired sites that mainly differed in aspect (SW vs. NE) and stand density (controls and thinning treatments). Nitrate was the only inorganic N form detectable in the soil water. Its concentration was high in control plots of the NE aspect, but only in canopy gaps and not influenced by thinning. Neither thinning nor aspect affected the abundance of root tips in the soil. Maximum nitrate net uptake by mycorrhizal fine roots of beech, however, differed with aspect, showing significantly lower values at the SW as- pect with warm–dry local climate. There were no clear- cut significant effects of local climate or thinning on microbial N conversion, but a tendency towards higher ammonification and nitrification and lower denitrifica- tion rates on the untreated controls of the SW as com- pared to the NE aspect. Apparently, the observed sensitivity of beech towards reduced soil water avail- ability is at least partially due to impaired N acquisition. This seems to be mainly a consequence of reduced N uptake capacity rather than of limited microbial re-sup- ply of inorganic N or of changed patterns of inorganic N partitioning between soil bacteria and roots. Keywords Nitrification Denitrification Ammonification Nitrate net uptake Fine root abundance Desorption solution Introduction European beech is the most important tree species of the potential natural vegetation in Central Europe (Ellen- berg 1992). However, due to forest management prac- tices in the last decades, forests within the natural distribution area of European beech are often domi- nated by conifer plantations (Moosmayer 2002). One of the most important aims of current forest policy is to reverse this development by supporting natural regen- A. Geßler (&) H. Rennenberg Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, Albert Ludwigs University of Freiburg, Georges-Ko¨hler-Allee 053/054, 79085 Freiburg, Germany E-mail: arthur.gessler@sonne.uni-freiburg.de Tel.: + 61-3-53214151 Fax: +61-3-5321-4166 K. Jung UFZ Umweltforschungszentrum Leipzig-Halle GmbH, Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany R. Gasche H. Papen A. Heidenfelder Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstrasse 19, 82467 Garmisch-Partenkirchen, Germany E. Bo¨rner B. Metzler Department of Forest Protection, Forestry Research Institute Baden-Wuerttemberg (FVA), Wonnhaldestr. 4, 79100 Freiburg, Germany S. Augustin E. Hildebrand Institute of Soil Science and Forest Nutrition, University of Freiburg, Bertholdstraße 17, 79085 Freiburg, Germany Present address: S. Augustin Federal Research Centre for Forestry and Forest Products, Institute for Forest Ecology and Forest Inventory, Alfred-Mo¨ller Street 1, 16225 Eberswalde, Germany Present address: School of Forest and Ecosystem Sciences, University of Melbourne, Water Street, Creswick, VIC, 3363 Australia Eur J Forest Res (2005) 124: 95–111 DOI 10.1007/s10342-005-0055-9