Emission Of Greenhouse Gas From Natural Broadleaved Forested Swamps And Its Response To Anthropogenic Disturbance In XiaoXing' An Mountains Of China

CO₂,CH₄ and N₂O are three most important atmospheric greenhouse gases,so study of their sources and sinks is one of the main areas of the terrestrial ecosystems and global change.Wetlands in Xiaoxing'an Mountains,which is one of the main distribution areas of mountains wetlands with the diversity types,play an important role in the wetlands study in China,therefore carrying out experimental research about sources and sink,affecting factors of greenhouse gases emission from the forested wetlands has an important scientific significance.So spatial and temporal variations, sources and sink,and affecting factors of CO₂,CH₄ and N₂O emission fluxes from Alnus sibirica swamp and a Betula platyphylla swamp,which are both types of broad-leaved forests swamp,were studied by using Static opaque chamber and gas chromatography technique in the growing season of 2007 and 2008 in Xiaoxing'an Mountains,at the same time,the effects of cutting(clear cutting, selective cutting 45%) on greenhouse gases emission from the forested wetlands were also measured. The results showed that:(1) CO₂ fluxes from most of wetlands in Xiaoxing'an Mountains peaked in spring or summer, and the rates kept at a low level in autumn until the lowest emissions of the end of autumn.Seasonal variations were correlated with temperatures and herb aboveground biomass,seasonal variations were correlated well with temperatures.(2) Diurnal variation of CO₂ fluxes was with a certain regularity,most of them were unique peak,and they hade the same pattern of diurnal fluxes in different seasons at the stone swamp,which the peak all occurred at higher temperature in the sample period.And the average Diurnal fluxes of CO₂ all took on summer＞spring＞autumn.(3) Apparent temporal and spatial variations of CO₂ fluxes from broad-leaved forest wetlands were observed in Xiaoxing'an Mountains.In the time scale,two kinds of broad-leaved forest wetlands soils both were the source of CO₂ in growing season,and the CO₂ fluxe in 2007 was significantly higher than that in 2008.In the spatial scale,CO₂ fluxe from Betula platyphylla swamp soil was higher than that from Alnus hirsuta swamp soil in growing season.Annual variations of CO₂ fluxes were controlled by the annual water table and temperatures,and the spatial variations of CO₂ fluxes were controlled by water table.(4) Apparent seasonal variations were observed in CH₄ fluxes,CH₄ fluxes from most of wetlands peaked in summer and autumn in Xiaoxing'an Mountains,and the rates kept at a low level in spring or late autumn.Seasonal variations were mainly affected by water level and temperature. Its seasonal variations were correlated more remarkable with temperatures when water table reached a certain height and no longer was a limiting factor.(5) Diurnal variation of CH₄ fluxes had certain regularity,most of them were unique peaks,and its diurnal variation took on the same pattern with unique peaks at the same time in different seasons. CH₄ diurnal fluxes from two types of broad-leaved forest wetland.all took on autumn＞spring＞summer.(6) The two kinds of broad-leaved forested wetlands both were the sources of CH₄,but there were large differences in time and spatial variations.In the time scale,CH₄ fluxes in 2008 were significantly higher than in 2007.In the spatial scale,CH₄ fluxes from Alnus hirsuta swamp were higher than that from Betula plalyphylla swamp in the growing season.Annual variations of CH₄ fluxes were controlled by the annual water table and temperatures,but the spatial variations of CH₄ fluxes were controlled by temperatures,water table and herb aboveground biomass.(7) N₂O fluxes from most of wetlands in Xiaoxing'an Mountains in the growing season peaked in summer or autumn,and appeared absorbing phenomenon in spring or late autumn.Seasonal variations were correlated more remarkable with temperatures.(8) The larger differences of diurnal variations were found in broad-leaved forest swamp,but most of them had the unique peak.N₂O fluxe of the Alnus hirsuta swamp took on the fluctuations at a relatively high level,otherwise that of Betula platyphylla swamp had the same pattern at the same time in difference seasons,which appeared to absorption phenomenon at night.N₂O diurnal fluxes of the Alnus hirsuta swamp displaied the autumn＞the summer＞the spring,and that of Betula platyphylla swamp did the summer＞the spring＞the autumn.(9) The two broad-leaved forested wetlands both were the source of N₂O in Xiaoxing'an Mountains,but large differences in time and spatial variations.In the time scale,N₂O fluxe in 2007 was significantly higher than that in 2008.In the spatial scale,N₂O fluxe of Alnus hirsuta swamp was higher than that of the Betula platyphylla swamp in the growing season.Annual variations of N₂O fluxes were controlled by the annual water table and temperatures,but water table and plant unique nitrogen-fixing ability may controlled the spatial variations of N₂O fluxes.(10) Greenhouse gas fluxes have greater differences after human harvesting(clear cutting, selective cutting 45%) between two broad-leaved forested swamps.The CO₂ fluxes all were increased besides the selective cutting Betula platyphylla swamp,the CH₄ fluxes all were decreased besides the clear cutting Betula platyphylla swamp,N₂O fluxes from logging Alnus hirsuta swamp had significant increase,and that from logging Betula platyphylla swamp had significant reduction. Changes in temperature and water table after cutting together contributed to the changes of ges fluxes of broad-leaved forest wetlands.From reducing the greenhouse gas emissions and the environment ecology of view considered,If we would make use of trees in the forested swamps,.we should choose selective cutting rather than clear cutting to protect its storage capacity for nutrient and control greehouse gas emission.