A Study On Forest Soil CO₂, N₂O And CH₄ Emission Flux And Dynamics In Xishan Area, Beijing

In this paper the emission flux and influence factors of some greenhouse gases as carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₀04 )from forest soils in Xishan area, Beijing will be discussed.The soil CO₂ emission was measured using alkaline absorption technique in three types of woodland ( new plantation .young growth and mature ) The result shows that the annual CO₂ emission flux ranges from -341.03 to 1193.59 mg.m^-2.h^-1 with mean of 286 mg.m^-2.h^-1. The CO₂ emission rate of three types of woodland have no remarkable difference in annual mean and similar seasonal variation tendency. But In the drier spring and early summer, the soil CO₂ flux of mature stand woodland is lower than that of young growth and new plantation woodland, and in the humid rainy season and autumn, the status is in opposite, even in winter the woodland soil absorbs CO₂.The emission flux of CO₂ has diurnal variation and the tendency is not the same along with three woodland types and four seasons. It is higher in daytime than in nighttime, and the time for occurring the highest and the lowest value is different.The emission flux of CO₂ is determined mainly by soil water contents., soil temperature and atmospheric pressure.The soil N₂O emission flux in the plantation of Acer truncatum and Piuns tabuleaformus woodland was measured in situ using static closed chamber technique. The annual N₂O emission flux ranges from -1.2 to 7.92μg. m^-2.h^-1 with mean of 3.16μg.m^-2.h^-1. It has seasonal variation as the highest flux in summer, the second in spring and autumn, and the lowest in winter. The N₂O emission flux is determined mainly by the precipitation within 5 days before , soil temperature and soil water contents.The N₂O emission rate also has undulated diurnal variation . It comes the lowest in 6'oclock and the peak in 9 and 18'oclock .This research shows the forest soils has very strong nitrification and denitrification. Moreover, the nitratase, nitritase and hydroxylamine reductase is very active.The static closed chamber technique was also used to study CH4 emission flux. The annual CH₄ emission flux ranges from 0 to 44.8μg. m^-2.h^-1 with mean of 20.47 μg.m^-2 .h^-1. CH4 absorption has a seasonal variation with a sequence of summer > spring and autumn > winter. The oxidization of CH₄ in forest soils appear mainly...