Methane consumption in a frequently nitrogen-fertilized and limed spruce forest soil after clear-cutting

The effects of especially frequent nitrogen (N) additions (from 1959 to 1986, totalling 860 kg N ha(-1)) and liming (in 1958 and 1980, totalling 6000 kg CaCO3 ha(-1)) on CH4 uptake by a boreal forest soil were studied in a stand of Norway spruce. Except for a forested reference plot, the stand was clear-cut in January 1993 and the following year one-half of each clear-cut plot was prepared by mounding. Fluxes of CH4 were measured with static chambers in the autumn before clear-cutting and during the following four summers. The average CH4 uptake during 1993-96 in the forested reference plot was 82 mug CH4 m(-2) h(-1) (ranging from 10 to 147 units). In the first summer after clear-cutting, the cleared plot showed 42% lower CH4 uptake rate than the forested reference plot, but thereafter the difference became less pronounced. The short-term decrease in CH4 consumption after clear-cutting was associated with increases in soil NH4+ and NO3- concentrations. Mounding tended at first to stimulate CH4 uptake but later to inhibit it. Neither liming nor N-fertilization had significant effects on CH4 consumption. Our results suggest that over the long term, in N-limited upland boreal forest soils, N addition does not decrease CH4 uptake by the soil.