关键词: 温带森林, 土壤, 温室气体, 排放量, 变化特征

Abstract: Using the enclosed chamber technique, CO₂, CH₄ and N₂O soil fluxes were measured during one year in a forest near Darmstadt, Germany. Fluxes measurements were made before (undisturbed forest soil) and after the removing of soil litter (leaves and humus layer) form the forest floor (disturbed soil). Gas fluxes from the removed leaves and humus were also measured. CH₄ and N₂O soil air concentration and soil moisture profile were measured during the period July to December.The average Fluxes from undisturbed forest soils are: 2800gCO₂/(m².a),-0.64gCH₄/(m².a), and 0.05gN₂O/(m²a). With the exception of N₂O signific4nt seasonal variation were observed, with the higher fluxes during thesummer. In general, the fluxes obtained in Darmstadt are in agreement with values reported for similar temperateforests. CO₂ and CH₄ fluxes show a significant dependence to changes in ambient temperature, whereas N₂Onuxes increase with soil moisture ranging between 7% and 20%, with an abrupt decrease at 22%. A goodcorrelation between CO₂ production and CH₄ consumption was observed, suggesting that methane uptake by soilsis related with the soil respiration process. No relationship was found between N₂O emissions rates and CO₂ orCH₄ fluxes.Very similar profiles of CH₄ in soil air (exponential concentration decrease with depth) were observed in allmeasurements, whereas N₂O profiles were highly related to the changes in soil moisture, e.g. higher concentrationof N₂O were found at the 20 to 50cm layer, during periods when the layer 0 to 15cm had relatively high soilmoistures.when the leaves and the layer of humus were removed from the forest floor, significant changes in thefluxes were observed, indicating that the litter layer plays an important role in the soil-atmosphere interaction. Inthe disturbed soil, CO₂ and N₂O emissions decrease in average by 23% and 50%, respectively, and CH₄consumption increase by 17%. The decrease of CO₂ emission is likely related to the activity of the removed humuslayer, that emits CO₂, however, the reduction in N₂O emission should to be mainly related to changes in theconditions (e.g. increase of oxygen concentration) in the active soil layer. Leaves and humus neither emit norconsume significant amounts of CH₄ and the increase of CH₄ consumption in the disturbed soil should be mainlydue to an increase of the transport of atmospheric CH₄ (and O₂) to the region where methane is consumed. Adecrease of the humus layer during last decades, due to effects of air pollution, has likely produced an increase ofthe consumption of atmospheric CH₄ by forest soils.

Key words: temperate forest soil, green-house gases, fluxes, variation