From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N ha-1 6 months-1 in the spruce soil and to 44.3 kg N ha-1 6 months-1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil (1.5 kg N ha-1 6 months-1) was less than in the spruce soil (5.9 kg N ha-1 6 months-1).

In the range of soil temperatures observed in the field (0 – +4°C), the temperature dependency of N net mineralization was low in the spruce soil. In the beech soil, the apparent temperature dependency of N net mineralization was much larger than in spruce and more pronounced in laboratory incubations than in the in situ incubations.

In temperate forest soils N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q10 values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle especially in deciduous forests.