火干扰对小兴安岭落叶松-苔草沼泽温室气体排放的影响

Effects of fire disturbance on greanhouse gas emission from Larix gmelinii-Carex schmidtii forested wetlands in XiaoXing′an Mountains,Northeast China

利用静态箱-气相色谱法,研究火烧干扰(轻度、重度)对小兴安岭落叶松-苔草沼泽生长季CO2、CH4、N2O排放的影响.结果表明:火烧干扰使CO2排放通量提高24.0%—45.9%,CH4提高135.1%(轻度)或下降31.3%(重度),N2O由吸收转化为排放.重度火烧改变了CO2的季节排放规律,火干扰改变了CH4与N2O的季节排放规律.火烧与未火烧样地CO2排放与水位呈显著负相关,与空气温度、土壤温度呈显著正相关;未火烧样地CH4排放与水位呈显著负相关,与地表温度呈显著正相关,轻度火烧样地CH4排放与气温和个别土壤温度呈显著正相关,而重度火烧样地CH4排放、各样地的N2O排放与水位和温度相关性均不显著.火干扰使CO2排放源强度较未火烧提高,轻度火烧样地CH4排放源强度较未火烧提高、重度样地则下降;N2O则由吸收汇转化为排放源.火烧样地温室效应贡献潜力较未火烧样地提高了1/4—1/2,且呈现出随火干扰强度增大而递增的变化规律。

A static chamber and gas chromatography were employed to investigate the effects of low- and high-intensity burning on CH4,CO2 and N2O discharge by larch swamp of the Lesser Xing′an Mountains.The results show that the average seasonal CH4,CO2 and N2O fluxes were respectively 409.7,508.1,and 597.8 mg·m–2·h–1 at sites where there was no burning,0.057,0.134 and 0.043 mg·m–2·h–1 at sites with low-intensity burning,and-0.0063,0.0021 and 0.0059 mg·m–2·h–1 at sites with high-intensity burning.Fire disturbance increased CO2 fluxes by 24.0%—45.9% and increased CH4 fluxes by 135.1% in the case of light burning and decreased CH4 fluxes by 31.3% in the case of heavy burning,and shifted the burning site from a N2O sink to a N2O source.Severe fire disturbance greatly affected the seasonal dynamics of CO2 fluxes,and the fire intensity affected seasonal variations in CH4 and N2O fluxes.CO2 emissions at the study sites had significant negative correlation with the water level,and the temperature had significant positive correlation with the soil temperature.CH4 emissions from the site at which there was low-intensity burning had significant negative correlation with the level of the water table and significant positive correlation with the soil temperature at 0 cm.The flux of CH4 emissions from the site with low-intensity burning had positive correlation with air temperature and some individual soil temperatures,whereas that from the site with high-intensity burning and the flux of N2O emissions from sites with low-intensity,high-intensity and no burning had no relationship with soil temperature or the level of the water table.The CO2 emission intensity at burning sites and CH4 emitted from the lightly burning site were both higher than respective values for the site where there was no burning,but the CH4 emission intensity from the heavily burning site was less than that at the site where there was no burning.Fire disturbance converted a site from a weak sink of N2O into a weak source.The global warming potential of the fire-disturbance sites increased by 1/4—1/2 relative to that of the site with no burning,with the potential increasing with the increasing intensity of the fire disturbance.Therefore,wetland management should be strengthened in view of the effective control of greenhouse gas emissions in wetlands,especially in terms of avoiding intense fire.In addition,both before and after fire in the investigated forest swamp,the effect of greenhouse gases mainly depends on the potential of soil CO2 emissions（99%）,and the role of N2O CH4 emissions is very small（a contribution of less than 1%）.It is thus necessary to research the carbon cycle.