新疆天山高寒草原不同放牧管理下的CO2,CH4和N2O通量特征

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With growing concerns on impacts of human activities and global warming on Alpine grasslands,comprehensive understanding of the sources and sinks of greenhouse gases becomes increasingly more important. The understanding is closely related to the progress on biogeochemical cycles of carbon and nitrogen in terrestrial ecosystems. Carbon dioxide, methane and nitrous oxide are the three most important greenhouse gases,which are considered to account for 80% contribution to global warming potential. The alpine grassland of Xinjiang is a typical temperate arid region of grasslands. The study was conducted at the Bayinbuluk Grassland Eco-system Research Station,Chinese Academy of Sciences( 83°43' E,42° 54' N). Bayinbuluk alpine grassland is located in the southern Tianshan mountains. Xinjiang Uygur AutonoMous Region,central Asia and covers a total area of approximately 2. 3 × 104km2. Bayinbuluk alpine grassland is the typicaltemperate arid alpine grassland,which is the second largest grassland of China after Inner Mongolia Grassland. As we all know,the grassland ecosystem has degenerated seriously and grazing prohibition is a frequently-used solution to prevent grass grassland degradation. While,it is still unknown that grazing prohibition impacts greenhouse gases fluxes in some degree. The study of carbon dioxide,methane and nitrous oxide of long-term grazing-prohibition grass( 1984),short-term grazing-prohibition grass( 2005) and free grazing grass in Bayinbuluk alpine grassland is meaningful,which will deepen our understanding of greenhouse gases fluxes in the alpine grassland ecosystem,help us assess global warming,parameterize Earth System models and get more comprehensive grasp of the impact of grazing prohibition on the grassland ecosystem. Using opaque,static,manual stainless steel chambers and gas chromatography,the fluxes of carbon dioxide,methane and nitrous oxide of long-term grazing-prohibition grass,short-term grazing-prohibition grass and free grazing grass were measured through the continuous experiment in situ from May 2010 to October 2011( no sampling in January and February 2011 because of the very low temperatures,about-40℃). Four times per month during the growing season( from May to October) and twice per month during non-growing( from November to next year April) season at all sites. According to the results of field experiment,the alpine grassland of Xinjiang is the sources of carbon dioxide and nitrous oxide; it is the sinks of methane. In the growing season,CO2average fluxes of short-term grazing-prohibition,long-term grazing-prohibition and free grazing are( 89.8 ± 49.3),( 52.8 ± 28.7),( 57.0 ± 30.7) mg·m-2·h-1; CH4fluxes averaged out to(- 66. 3 ± 21. 3),(-104.5±32.8),(-103.0±39.0) μg·m-2·h-1; CH4fluxes averaged out to( 21.2 ± 11.8),( 13.6 ± 6.9),( 13.2 ± 6.2) μg·m-2·h-1. Our results indicated that:( 1) Nitrous oxide fluxes showed a significant correlation with carbon dioxide fluxes in three kinds of grasslands.( 2) In the growing season,the difference of greenhouse gases fluxes between long-term grazing-prohibition grass and free grazing grass were not significant,while short-term grazing-prohibition grass has higher fluxes of carbon dioxide and nitrous oxide and lower fluxes of methane.( 3) In growing season,the fluxes of methane of short-term grazing-prohibition grass showed significant difference with long-term grazing-prohibition grass and free grazing grass. But the difference of growing-season average carbon dioxide and nitrous oxide fluxes did not reach the significance level of 0.05.( 4) In non-growing season,no significant differences between the fluxes of carbon dioxide,methane and nitrous oxide were found in long-term grazing-prohibition grassland,short-term grazing-prohibition grassland and free grazing grassland.