Four years continuous record of CH(4)-exchange between the atmosphere and untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany

In order to gain information about seasonal and interannual variations of CH(4)-fluxes at a spruce control site, a limed spruce site and a beech site of the Hoglwald Forest, Bavaria, Germany, complete annual cycles of CH(4)-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH(4) fluxes observed for the different sites were: +12.4 to -69.4 mug CH(4) m(-2) h(-1) (spruce control site), +11.7 to -51.4 mug CH(4) m(-2) h(-1) (limed spruce site), and -4.4 to -167.3 mug CH(4) m(-2) h(-1) (beech site). Lowest rates of atmospheric CH(4)-uptake or even a weak net-emission of CH(4) by the soils were observed during winter/spring times, whereas highest rates of CH(4)-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH(4)-uptake rates were -1.82 kg CH(4)-C ha(-1) yr(-1) at the spruce control site, -1.31 kg CH(4)-C ha(-1) yr(-1) at the limed spruce site, and - 4.84 kg CH(4)-C ha(-1) yr(-1) at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH(4)-fluxes of approx. 1 kg CH(4)-C ha(-1) yr(-1), multiple year measurements of CH(4)-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH(4). By comparison of CH(4)-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH(4)-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH(4)-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH(4)-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH(4) fluxes were soil moisture and soil temperature. Field measurements of CH(4) concentrations in the soil profile and laboratory measurements of CH(4)-oxidation and CH(4)-production activity on soil samples taken from different soil depths showed that the CH(4)-flux at the Hoglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH(4) within the soil. Highest CH(4)-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH(4)-production activity was found in the organic layer.