Study On The Emission Flux Of Greenhouse Gases From Cropland Soils And The Soil Carbon Sink In China

Global change resulted mainly from increased concentration of atmospheric greenhouse gases has becoming the worldwide concrn. 70-90% of atmospheric CH₄ and N₂O are produced from soil microbial processes, and the land use and land-use change resulted CO₂ emissions also contribute to climate warming. The agroecosystem contributed to climate change through emission N₂O from dryland soils and CH₄ from paddy soils. While available mitigation options could debate these trends. Based on these backgrounds, this paper focus on the follow aspects, they are:â…°) The seasonal variation of greenhouse gases (CO₂, CH₄, N₂O) and their relationships with relative soil indexes such as soil inorganic nitrogen, and soil humidity and other management activities such as fertilization and irrigation etc. from typical dryland soils and paddy soils,â…±) The soil carbon stocks and its distribution characters in geographical spaces in China.â…²) The carbon sequestration potential of activities under Article 3.3 and 3.4 of Kyoto Protocol in China and some implications of these activities on the implementation of commitment of Annex-I countries since sinks were introduced by the Kyoto Protocol. The results are as follows:(1). The soil CO₂ emission flux correlated with the growth status of crops: at the stages when plants and roots grew quickly and when the amount of plant debris was more, soil CO₂ emission flux showed higher due to the large amount of root exudations and organic material as the substrate of soil microorganisms;(2). Soil dissolved organic carbon (DOC) could not exactly reflect the soil respiration intensity. This is perhaps because DOC is not only one of the intermal products of decomposition process of complicated plant material, but also it could be decomposed further by microorganisms and this process is quickly happened under higher temperature and proper soil water content;(3). The N₂O flux was positively correlated with soil inorganic N content mostly resulted from applications especially under higher temperature and proper soil humidity conditions;(4). The typical cropland was a weak net CH₄ sink with the average flux of-0.003～-0.025 mg CH₄/m²/h, and the higher soil humidity could decrease the methane absorption intensity of dryland soils;(5). Under the condition of this experiment, aeration at later tillering stage of single rice growth period could decrease methane emission by 16.1%; while the increased N₂O production only accounted for 7.3% of the total GWP (methane+N₂O) (in the 500years time scale);(6). The carbon sequestration potential of the seven items of activities under Article 3.4 of Kyoto Protocol is 104.9 MMtC/y with the range of 62.7～233.2 MMtC/y in China in the future. Among these potentials, their contributions are in the order: forest management＞grassland management＞cropland management.(7). Annex-I countries could complement 50～70% of their mitigation commitments when activities under Article 3.3 and 3.4 were adopted.(8). The total carbon stocks of Chinese soils in the 0～94cm soils were 107.5 Gt in the 1980's. And the carbon stocks of 0～20, 0～51, and 0～84cm soil depths accounted for 38%, 77%, and 98% of the total stocks respectively.(9). The geographical distribution rules of soil carbon stocks in China were: with the increase of latitude along the East China, the soil carbon density increased; And with the decrease of longitude along the North China, the soil carbon density decreased.