Research On Fluxes Of Greenhouse Gas Of Temperate Forest Ecosystems In Northeastern China

Temporal dynamics of greenhouse gases fluxes and theirs controlling factors for three representative temperate forests in northeastern China were examined with a static closed chamber-gas chromatograph technique.These forests were Korean pine(Pinus koraiensis) plantation,Dahurian larch(Larix gmelinii) plantation and hardwood broadleaved forest (dominated by Fraxinus mandshurica,Juglans mandshurica,and Phellodendron amurense). The results showed:All ecosystems were overall atmospheric N₂O source during the growing season.The N₂O flux(μg·m^-2·h^-1) decreased in order of the hardwood broadleaved forest(21.0±4.9) > the pine plantation(17.6±4.6) > the larch plantation(9.8±5.9).Overall,there was no consistent seasonal pattern in N₂O flux for the four ecosystems.The N₂O flux was significantly positively correlated to soil gravimetric water content(0-10 cm depth) consistently for all ecosystems,but significantly negatively correlated to NO₃^--N content for each ecosystem.However,the responses of N₂O flux to soil temperature and NH₄⁺-N differed among ecosystems.The N₂O fluxes for the coniferous plantations were positively correlated to NH₄⁺-N,but not correlated to the soil temperature at 5 cm depth;while those for the broadleaved forests displayed an opposite trend.The soil water content was the dominator of soil N₂O emission for the forests in 2007 perhaps resulting from relative drought in the year.Interactions of vegetation type, environmental factor,nitrogen availability to soil N₂O emission should be further studied in the future.During the spring soil thawing period,all ecosystems overall behaved as atmospheric CO₂ source and CH₄ sink,the fluxes decreased in order of the hardwood broadleaved forest > the larch plantation > the pine plantation.There were no singifieantly differences in CO₂ fluxes of the three ecosystems,but they singifieantly differed in CH₄ fluxes(P<0.05).The dynamics of CO₂ fluxes and soil gravimetric water content showed similar patterns,and they Peaked in the mid of the spring soil thawing.The dynamics of CH₄ fluxes and soil temperature both showed bell-shaped curves,with absorption peaks in the end of the spring soil thawing.The CO₂ flux was significantly positively correlated to soil gravimetric water content(0-10 cm depth) consistently for all ecosystems,the release of soil CO₂ was affected by microbial biomass C,N in varying degrees,CH₄ flux was significantly negatively correlated to soil temperature at 5 cm depth for each ecosystem,soil nitrogen restricted CH₄ absorption.