EFFECTS OF A TEMPERATURE INCREASE IN A FI ELD EXPERIMENT ON THE NITROGEN RELEASE FROM SOIL CORES WITH DIFFERENT HUMUS FORMS

Global warming could have far-reaching consequences for the properties of soils. From the available knowledge it is postulated that an incre ase in temperature (ail other climatic conditions unchanged) will decr ease the nitrogen contents until a new equilibrium is reached. To test this hypothesis we established in the 'Tegernsee Alps' a field experi ment. In spruce-dominated montane forests 60 undisturbed soil cores (= monoliths) were carefully digged out at 1250 and 1320 m asl and reest ablished at 3 elevations (1250 m and 1010 m and at 740 m asl) correspo nding to a warming of around 1 and 2 degrees C. At each slope position we investigated a Dystric Cambisol with raw humus (RH) and another on e with moder (MO). Each of these 6 trial-variants therefore was repres ented by 10 monoliths. From August 1992 to December 1995 seepage water was sampled by suction cups every 2 or 4 weeks and analyzed for the c oncentrations of important bioelements including aluminum, pH and elec trical conductivity. After translocation to warmer climates additional nitrogen was released from both soil forms mainly as nitrate. The Cam bisol with the more active humus form moder reacted stronger than the one with raw humus (additional output > 40 vs. 34 kg ha(-1) a(-1); +2 degrees C). In both soil forms the N release was accelerated in summer , in RH by 55 to 92 and in MO by 37 to 86 ppm. The Cambisol with moder showed higher nitrate leaching also in winter and thus was superior w ith regard to the total annual N output. In all cases Al was the most important associated cation to NO3- with 75% (RH) and 54% (MO) of the cation equivalent sum respectively The experiment thus confirms a subs tantial increase of nitrification even by a temperature increase of on ly 1 and 2 degrees C, which in permeable, well aerated sails should le ad to increased nitrate leaching under conditions where no vegetation is interfering.