Study On Greenhouse Gas Emission For Grassland Soil Below Different Forest Soils Under Precipitation Reduction And Nitrogen Deposition In Shennongjia Mountain

Global climatic change and nitrogen deposition are key focus for scientists.Fluxes of soil greenhouse gas had been varied under global climatic change.Shennongjia, locating in the ecological zones of evergreen-deciduous broad-leavedforests in Qinling-Bashan Mountain, is typically characterized by northern subtropicalforest ecosystems. It is important to study the emission fluxes and their mechanismsof greenhouse gas from typical forest ecosystems in Shennongjia for coping with thechallenge of future climate change.In this study, we chose one typical natural forest （evergreen-deciduousbroad-leaved forests） and two types of plantation （Pinus massoniana plantation andChinese Fir plantation） in Shennongjia to explore the effects of precipitation changeand nitrogen deposition on greenhouse gas fluxes during the growing season fromJune to October2012. The research results showed that:（1） Both the soil of typical natural forest and the two types of plantation werethe source of CO₂and N₂O, but were the sink of CH₄under the treatments of eitherhalf reduction in precipitation or nitrogen deposition.（2） When the transpiration was reduced by50%, the emission flux of CO₂increased significantly in evergreen and deciduous broad-leaved mixed forests and theChinese Fir plantation. And the flux of CO₂absorption decreased in Pinusmassoniana plantation. At the same treatment, the flux of CH₄absorption increasedsignificantly in evergreen and deciduous broad-leaved mixed forests and the ChineseFir plantation, but the flux of its absorption decreased in Pinus massoniana plantation.The half reduction of transpiration have promoted the absorption of N₂O by the soil ofevergreen and deciduous broad-leaved mixed forests and Pinus massoniana plantation,but the treatment prohibited the emission of N₂O from the soil of Chinese Firplantation.（3）The Nitrogen treatment prohibited the CO₂emission flux and the CH₄absorption flux of the soil in Pinus massoniana plantation. The emission of CO₂wasreduced by20.52%and the absorption of CH₄by44.1%from June to July or by40.7%from August to October, but the emission of N₂O flux was increased by7.95%in Pinus massoniana plantation.（4） The CO₂fluxes in Pinus massoniana and Chinese Fir plantations werehigher42%and36%than that of evergreen deciduous broad-leaved mixed naturalforests. The absorption of CH₄flux by the soils of two plantations was significantlylower61%and72%than that of the typical natural forests. And the emission of N₂Ofluxes in the soils for two plantations were lower85%and96%than that of thetypical forests, respectively.（5） In three types of forests, the air temperature and the soil thermometersexhibited the same seasonal rhythm. The soil temperature （BST） of evergreen anddeciduous broad-leaved mixed forest was slightly lower than that of the pine （PST）and Chinese Fir plantation （CST）. Before October, the air temperature wassignificantly higher than the soil temperature, but after October, the air temperaturewas lower than the soil temperature. In three types of forests, the CO₂flux wassignificantly related to the air temperature and the soil temperature, the correlationcoefficient was ranged0.58to0.77.