Wetlands are important sources and sinks of greenhouse gases. Fire is an important disturbance factor in forested wetlands, the forestry of fire disturbance were 1% per year on average in the global. Fire-related disturbance in forests are more frequent in mid-to high latitudes than elsewhere. In the present study, two kinds of forested wetlands; Carex schmidtii wetland and Betula ovalifolia-Carex schmidtii shrub wetland, were studied to reveal the emission variation of CH₄, CO₂, and N₂O under fire disturbance during the growing season. The study area is located in the Lesser Xing'an Mountains. We used a static opaque chamber and gas chromatography methods, and we monitored related environmental factors. The results were as follows: disturbance by fire increased air and soil temperature by 0.1-2.0℃, and lowered the water table by an average of 2.7 cm. Burning increased CH₄ emissions from marsh and shrub wetlands by 56% and 524.9%, respectively. Burning decreased the CO₂ and N₂O emissions by 27.1% and 64.9% respectively from the marsh, and 27.1% and 64.9% from the shrub wetland. Burning also changed the marsh wetland CO₂ and shrub wetland N₂O flux patterns in the growing season, but no marked variations were detected in the marsh wetland CH₄ and N₂O, and in the shrub wetland CO₂ flux patterns.
The CH₄ emissions and the seasonal change pattern were affected by fire disturbance. Before and after the fire disturbance, CH₄ emission flux remained unchanged during the growing season. The CH₄ was absorbed weakly by the wetland soil in spring and emitted in summer and autumn. The CH₄ emission flux in summer was less than that in autumn. However, the CO₂ and N₂O emission fluxes had changed. At the unburned site, the CO₂ flux had a seasonal variation where summer flux > spring > autumn; under fire disturbance, the CO₂ flux in summer > autumn> spring. The N₂O flux varied in the order of spring > summer > autumn under no fire disturbance, but under slight fire disturbance, the order was spring > summer >autumn. The CH₄ flux from the reference marsh wetland plot (unburned) was significantly correlated (P<0.05) with soil temperature at 5 cm depth, but it was not correlated with water table depth in the burned plot. No significant correlations were found between CH₄ flux and soil temperature in any soil horizons, or with water table depth in the shrub wetland. In the reference plots of shrub wetland and marsh wetland, the CO₂ flux had a significant positive correlation (P<0.05) with soil temperature at depths between 0-15 cm; at burned sites, the CO₂ flux had a highly positive correlation with soil temperature in the 0-30 cm depth. Fire disturbance enhanced CH₄ emission intensity, and reduced the CO₂ and N₂O emissions. Under such circumstances, the global warming potential at burned sites would be decreased by 23.3%. Therefore, fire disturbance could decrease the emission of greenhouse gases from the two types of forested wetlands. Statistically significant negative correlation (P<0.05) was found between CO₂ flux and water table depth within marsh, reference and burned plots of shrub wetlands. Burning increased CH₄ emission intensity, and reduced the CO₂ and N₂O emissions. The global warming potential at burned sites decreased by 23.3%. Therefore, fire disturbance could decrease the emission of greenhouse gases from the two types of forested wetlands.