Control of Nitrification by Tree Species in a Common-Garden Experiment Kasaina Sitraka Andrianarisoa, 1 * Bernd Zeller, 1 Frank Poly, 2 Henri Siegenfuhr, 1 Severine Bienaime ´, 1 Jacques Ranger, 1 and Etienne Dambrine 1 1 INRA, UR 1138 Bioge ´ ochimie des Ecosyste ` mes Forestiers, 54280 Champenoux, France; 2 INRA-CNRS, UMR 5557, USC 1193, Ecologie Microbienne Universite ´ de Lyon, bat. G. Mendel, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, France ABSTRACT We studied the effect of tree species on nitrification in five young plantations and an old native beech coppice forest at the Breuil experimental site in central France. The potential net nitrification (PNN) of soil was high in beech, Corsican pine, and Douglas fir plantations (high nitrifying stands denoted H) and low in spruce and Nordmann fir plantations as well as in native forest stands (low nitrifying stands denoted L). We hypothesized that tree species would stimulate or inhibit nitrification in transplanted soil cores within a few years after the cores were transplanted between stands. We first initiated a transplant experiment where soil cores were exchanged between all stands. The PNN remained high in soil cores from H transferred to H and low in soil cores from L transferred to L. The PNN increased considerably after 16 months in soil cores transferred from L to H, whereas the transfer of soil cores from H to L decreased the PNN only slightly after 28 months. In a second transplant experiment, forest floor material was exchanged between the Douglas fir (H) and the native forest (L) stand. Six months later, the forest floor from the native forest had increased the PNN of the Douglas fir soil considerably, whereas the forest floor from Douglas fir did not affect the PNN of the soil in the native forest stand. It was concluded that beech, Corsican pine, and Douglas fir rapidly stimulate soil nitrification by either activation of suppressed nitrifier communities and/or colonization by new nitrifier communities. Conversely, the slow and irregular reduction of nitrification in spruce, Nord- mann fir, and native forest was probably due to the low and heterogeneously distributed flux of inhib- iting substances per volume of soil. Our experi- ments suggest that the inhibition of nitrification is not tightly connected to forest floor leachates, but that the forest floor both reflects and maintains the major ongoing processes. In the long term, humus build up and the production of inhibiting substances may completely block the nitrification activity. Key words: forest ecosystems; potential net nitrification; tree species; soil core exchanges; forest floor exchanges; nitrate concentration. INTRODUCTION In most ecosystems, nitrogen (N) mineralization and nitrification supply mineral N to plants. Nitri- fication determines the form of N present in the soil and, therefore, how N is absorbed or dispersed into the environment. The assessment of nitrification is Received 11 June 2009; accepted 23 June 2010; published online 16 October 2010 Author Contributions: Kasaina Sitraka Andrianarisoa conceived of or designed study, performed research, analyzed data and wrote the paper. Bernd Zeller conceived of or designed study, performed research. Frank Poly conceived of or designed study. Henri Siegenfuhr performed research, analyzed data. Severine Bienaime ´ performed research. Jacques Ranger conceived of or designed study. Etienne Dambrine conceived of or designed study, analyzed data, and wrote the paper. *Corresponding author; e-mail: andrianarisoak@yahoo.fr Ecosystems (2010) 13: 1171–1187 DOI: 10.1007/s10021-010-9390-x Ó 2010 Springer Science+Business Media, LLC 1171