Wetlands are important sources and sinks of greenhouse gases. Fire disturbance plays an important role in wetland ecosystems. it commonly is a important carbon sink of the land ecosystems, the Lesser xing'an Mountains of China's northeast is the frequent area of the fire disturbance as well as a major distribution area of China's wetlands. Fire-related disturbance in forests are more frequent in mid-to high latitudes than elsewhere. In the present study, Alnus sibirica 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 2.5-5.0℃, and lowered the water table by an average of 0.24-6.36 cm. Burning increased CH₄ emissions from Alnus sibirica wetlands by 485.2. Burning decreased the CO₂ and N₂O emissions by 45.5% and 24.8% respectively from Alnus sibirica wetland. Burning also changed the Alnus sibirica wetland CO₂ and N₂O flux patterns in the growing season, but no marked variations were detected in the Alnus sibirica wetland CH₄.
Burning changed the Alnus sibirica wetland green-house gas flux patterns in the growing season.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(M₀,M₁) in spring and emitted in summer and autumn. The CH₄ emission flux in summer was less than that in autumn. 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 > autumn > summer 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 15 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 Alnus sibirica wetland. In the reference plots of Alnus sibirica 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 43.34%. Therefore, fire disturbance could decrease the emission of greenhouse gases from the Alnus sibirica 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 Alnus sibirica wetlands. Burning increased CH₄ emission intensity, and reduced the CO₂ and N₂O emissions. The global warming potential at burned sites decreased by 43.34%. Therefore, fire disturbance could decrease the emission of greenhouse gases from the Alnus sibirica of forested wetlands.