Liming practice in temperate forest ecosystems and the effects on CO 2 , N 2 O and CH 4 fluxes

The effect of superficial liming of acidic forest soils on CO 2 and N 2 O emissions and CH 4 uptake was investigated with closed chambers in two deciduous and two spruce forests, by weekly to biweekly measurements over at least one year. The flux rates of untreated areas varied between 1.94 and 4.38 t CO 2 ‐C/ha per y, 0.28 and 2.15 kg/N 2 O‐N/ha per y and between 0.15 and 1.06 kg CH 4 ‐C/ha per y. Liming had no clear effect on CO 2 emissions which may change in the long‐term with decreasing root turnover and increasing C‐mineralization. Apart from one exception, liming resulted in a reduction of N 2 O emissions by 9 to 62% and in an increase of CH 4 uptake by 26 to 580%. The variability in N 2 O emissions between the forest sites could not be explained. In contrast, the variability of annual CH 4 uptake rates could be explained by N content ( r 2 = 0.82), C content ( r 2 = 0.77), bulk density ( r 2 = 60), pore space ( r 2 = 0.59) and pH ( r 2 = 0.40) of mineral soil at a depth of 0 to 10 cm, and by the quantity of material in the organic layer ( r 2 = 0.66). Experiments with undisturbed columns of the same soils showed that between 1 and 73% of the total N 2 O emissions came from the organic layer. However, atmospheric CH 4 was not oxidized in this layer, which represents a diffusion barrier for atmospheric CH 4 . When this barrier was removed, CH 4 uptake by the mineral soil increased by 25 to 171%. These results suggest that liming of acidic forest soils causes a reduction of the greenhouse gases N 2 O and CH 4 in the atmosphere, due to changes in the chemical, biological, and physical condition of the soils.