THE NITROGEN BUDGET OF A UPPER MONTANE FOREST ECOSYSTEM IN THE TEGERNSEE ALPS IN DEPENDENCE ON THE SEASONAL WEATHER

The nitrogen budget of a montane forest ecosystem in the Bavarian Alps was investigated from summer 1993 to winter 1995/96 in dependence on seasonal weather in the project ''The influence of climate change on t he nitrogen budget of forest soils''. The N-budgets were calculated by the nitrogen input via throughfall and the nitrogen output by seepage water, that has been sampled using suction cups. The hypothesis of a more positiv nitrogen budget of the ecosystem in warmer summers - nitr ogen input is greater than nitrogen output - could neither be confirme d nor rejected, because there were no two summers differing solely in temperature. Rather, the variable precipitation regime during the summ er season predominates a potentially changed nitrogen uptake by vegeta tion In the investigated ecosystem, the nitrogen budget is less positi ve if the precipitation is higher and/or the average temperature of th e air is lower. Also, for winter periods with higher precipitation we calculated a lower rate of nitrogen accumulation or even a nitrogen lo ss. On the other hand, higher temperatures will cause accelerated nitr ogen accumulation This is explained by the importance of high nitrogen inputs via throughfall in winter. The sequestration of potentially mo bile nitrate-N in organic matter, and thus its retention in the ecosys tem, demands a certain degree of humus activity. This activity is dimi nished at low temperatures.