Nitrogen transformations in a forested catchment in southern Norway subjected to elevated temperature and CO2

Model predictions on the response of soil processes to global warming are mostly inferred from small-scale laboratory studies. In this study, a forested catchment in southern Norway was enclosed by a greenhouse and experimentally manipulated by increasing CO2 (+200 mu l l(-1) above ambient) and temperature (+3-5 degrees C). This paper reports on the effects of the climate manipulation on N mineralization and nitrification. We measured net N mineralization and nitrification in a control and treated part of the greenhouse as well as in an uncovered reference catchment in plots dominated by Calluna vulgaris (L.) Hull or Vaccinium myrtillus L. Net N mineralization in the 0-10 cm soil layer significantly increased, most likely as a result of increased temperature. The effect was largest in plots dominated by Calluna. Nitrification did not significantly increase. Soil moisture inside the incubated cores was not affected by the climate change treatment. Pre-treatment mineralization was similar inside and outside the enclosure whereas nitrification was higher inside the enclosure. The NH4+ content was significantly lower inside the chamber due to removal of acidifying components from the precipitation and lower inputs of dry deposition. We found however no differences in pH, %C and %N of the LF and H layer and total C and N in the soil cores between the two catchments. Mineralization was generally higher under Vaccinium than under Calluna even though measured soil chemical and physical characteristics were similar. Nitrification was higher under Calluna than under Vaccinium. (C) 2000 Elsevier Science B.V. All rights reserved.