Study On CO 2 And CH 4 Fluxes In Artificial Grassland And Woodland Soils

Global warming caused by greenhouse gases is one of the most important environmental problems, which deeply influence the sustainable development of human society and survival. Research on greenhouse gases emission of the terrestrial ecosystem is a hot issue in recent years. As a complicated component of the terrestrial ecosystem, artificial grassland and forest land is strongly influenced by human activities. However, very few studies have been conducted on greenhouse flux of artificial grassland and forest land. The research investigated the diurnal and seasonal variations of greenhouse fluxes ?CO₂ and CH₄? of artificial grassland and forest land in the northwest of China, using LGR ultra portable greenhouse gas analyzer and SF-3000 soil greenhouse gas flux measuring system. Meanwhile the variations of CO₂ and CH₄ fluxes and the influence of environmental are discussed, while a comparison of different types of grassland and forest land as well as nature ecosystems are made. The main results are as follows:?1? Variation of soil CO₂ flux and its influence factors of artificial grasslandIn artificial grassland, soil CO₂ flux exhibited an obvious seasonal variation. The mean value of soil CO₂ flux was 0.06?mol m^-2s^-1 which reflected the sources of CO₂ in the year. The seasonal variation of soil CO₂ flux was different. The maximum CO₂ flux value was 0.27?mol m^-2s^-1 appeared in May, while the minimum was -0.35?imol m^-2s^-1 appeared in January. Temperature is the main factor that influence the seasonal variation, especially the temperature of soil at 5 cm depth ?T5?.In artificial grassland, soil CO₂ flux also exhibited an obvious diurnal variation. Mean value and variability of the fluxes were higher during the daytime than that at night. Mean value of soil CO₂ flux was 0.09?mol m^-2s^-1 which reflected the sources of CO₂. The maximum diurnal mean flux was appeared in 12:00^-14:00?Beijing time?, while the minimum was appeared in 8:00^-10:00. The maximum value of soil CO₂ flux appeared slightly earlier than the maximum temperature of atmospheric temperature and soil temperature. Temperature is the main factor that influence the diurnal variation, especially the temperature of soil at 5cm ?T5? and 10cm depth ?T10?.?2? Variation of soil CH₄ flux and its environmental factors in artificial grasslandSoil CH₄ flux also exhibited an obvious seasonal variation in artificial grassland. The seasonal variation of soil CH₄ flux showed the maximum value appeared in summer and the minimum one in winter. During the observation period, the soil CH₄ flux fluctuated between -0.05nmol m^-2s^-1—0.25nmol m^-2s^-1, and the mean value was 0.08nmol m^-2s^-1, which reflected the sources of CH₄. The maximum CH₄ flux value was appeared in February, while the minimum was appeared in December. There is no main environmental factor influences the seasonal variation soil CH₄ flux of artificial grassland, so the result may be caused by interaction of all environmental factors.In artificial grassland, soil CH₄ flux also exhibited an obvious diurnal variation. The volatility of the day is large, the scope of the night fluctuations is very small. During the observation period, the soil CH₄ flux fluctuated between^-1.13 nmol m^-2s^-1-2.77nmol m^-2s^-1, and the mean value was 0.07nmol m^-2s^-1, which reflected the sources of CH₄. The maximum diurnal flux value appeared in 16:00^-18:00?Beijing time?, while the minimum was appeared in 8:00^-10:00. In the afternoon, there will be a large fluctuation appeared. Temperature is also the main factor that influence the diurnal variation, especially the temperature of soil at 10cm depth ?T10?.?3? Variation of soil CO₂ flux and its environmental factors in artificial forest landThe seasonal variation of soil CO₂ flux in artificial forest land is characterized by high flux value in spring and summer, and relatively low in winter. During the observation, the average flux value was 1.06?mol m^-2s^-1, the maximum value was 4.6?mol m^-2s^-1 appeared in May, and the minimum one was 0.06?mol m^-2s^-1 appeared in October. Meanwhile, the flux fluctuant range is wide. Soil temperature of 5cm depth is the main environmental factor that influence its variation.Soil CO₂ flux in artificial forest land also exhibited an obvious diurnal variation. The volatility of the day is large, the scope of the night fluctuations is small. The maximum diurnal flux was appeared in 11:30^-13:30?Beijing time?, while the minimum was appeared in 7:30-9:30. Mean value of soil CO₂ flux was 1.13?mol m^-2s^-1 which reflected the sources of CO₂ in diurnal variation. Soil temperature could explain most variation of soil CO₂ flux. On diurnal scale, soil temperature at the depth of 10 cm ?T10? was the main factor which most closely related to soil CO₂ flux.?4? Variation of soil CH₄ flux and its environmental factors in artificial forest landThe value CH₄ flux of artificial forest land soil was negative during February to July, November and December, which reflected the absorption of CH₄. The other month was positive, which reflected the source of CH₄. During the observation period, the soil CH₄ flux fluctuated between -0.3 nmol m^-2s^-1-0.24nmol m^-2s^-1, and the mean value was-0.03nmol m^-2s^-1, which reflected the absorption of CH₄. Soil CH₄ flux is not significantly correlated with all environmental factors. Soil CH₄ flux in artificial forest land also exhibited an obvious diurnal variation. The volatility of the day is large, the scope of the night fluctuations is small. The maximum diurnal flux was appeared in 7:00-9:00 ?Beijing time?, while the minimum was appeared in 16:00^-18:00. Mean value of soil CH₄ flux was 0.16?mol m^-2s^-1 which reflected the absorption of CH₄ in diurnal variation. There are no major restrictive environmental factors that affect its diurnal variaition.