CH4 UPTAKE BY TEMPERATE FOREST SOIL - EFFECT OF N INPUT AND SOIL ACIDIFICATION

N fertilization and soil acidification effects on the uptake of atmospheric CH4 and soil CH4 concentrations were studied in lysimeter soil from a 100-y-old Scots pine forest in Norway. N fertilization with NH4NO3 significantly reduced the uptake of atmospheric CH4. Medium N application (30 kg N ha(-1) y(-1)) resulted in a CH4 uptake rate which was 85 +/- 3% of that in the control. while the uptake rate with high N (90 kg N ha(-1) y(-1)) was 62 +/- 2% of the control. The most acidic irrigation (pH = 3) increased CH4 uptake compared to pH 5.5 and 4 irrigations. This effect was the same at all N treatments (no interaction). The positive effect of acidification indicates that autotrophic NH4 oxidation is of minor importance for CH4 oxidation in soil. Increased soil moisture from 32 to 42% (v/v) significantly reduced CH4 uptake. CH4 uptake was observed during winter measurements, when the mean soil temperature was <1 degrees C.