随着对气候变化日趋关注，人们对生态系统气体交换及其主要影响因素进行了大量研究。短花针茅草原作为荒漠草原的典型代表，是亚洲特有的一种草原类型，是最干旱的草原类型，生态环境异常严酷，系统极度脆弱，稳定性差，在自然和人为干扰下极易退化。以短花针茅（Stipa breviflora）草原为研究对象，通过控制降雨量以及氮素添加对生态系统气体交换进行监测，研究气体交换对降雨量和氮素添加的响应过程，揭示降雨量和氮素添加对生态系统气体交换的影响作用。该文在2012年自然条件下，采用自动CO2通量系统（Li-6400, Li-COR, Lincoln, NE, USA）野外测定短花针茅（Stipa breviflora）草原生态系统气体交换数据，比较研究了增雨施肥（WN）、增雨不施肥（W）、减雨施肥（RN）、减雨不施肥（R）、单独施肥（N）、自然状况（CK）条件下2012年气体交换变化规律。结果表明：整个生长季生态系统净 CO2交换（NEE）、总的生态系统生产力（GEP）、生态系统呼吸值（ER）都呈先升高后降低的趋势，并在生长旺盛期（8月）达到最大值。NEE在N、W处理下有升高，其他处理都降低。ER在N、WN处理下都有升高，其他处理都降低。GEP在W、N、WN处理下都有升高，其他处理都降低。NEE、ER、GEP都是在N处理中达到最大值。%As the main Chinese grassland region and part of the world’s largest contiguous arid and semi-arid steppe ecosystem, the desert steppe of Inner Mongolian plays an increasingly important role in environmental conservation and global climate change. However, this ecosystem has been severely degraded in recent decades due to poor management and increasing human pressures. As a typical desert steppe, stipa breviflora steppe is mainly located in the drought area in Inner Mongolia. Since nitrogen is an important limiting factor in desert steppe of Inner Mongolian, the application of nitrogen may be a useful approach to restore degraded grasslands and increase carbon sequestration. However, the uptake of applied nitrogen mainly depends on water availability. In arid and semiarid ecosystems, rainfall is often the first limiting factor for plant growth and productivity, in which case nitrogen fertilization may only be effective at increasing rangeland production in wet years. The ecosystem gas exchange is a very important indicator in evaluating carbon cycle of terrestrial ecosystems. However, limited studies can be found to address how the water and nitrogen affect the the ecosystem gas exchange in desert steppe. In the present study, the main objectives were to investigate the response of the ecosystem gas exchange to rainfall and nitrogen fertilizer application and to study the interactive effects of water and nitrogen on the ecosystem gas exchange in the stipa breviflora steppe. A comparative study of different water and nitrogen treatments was conducted in the Desert Steppe of Siziwang County in Inner Mongolia, P. R. China in 2012. The randomized complete block design was used with three replications and two nitrogen levels and three water treatments. The nitrogen rates were 0 and 100 kg N ha-1. The three water treatments consisted of control (local annual average rainfall of 58 mm), 70%of control and 130%of control. Under the nature condition, the ecosystem gas exchange was measured by using LI-6400(Li-6400, Li-COR, Lincoln, NE, USA)in the stipa breviflora steppe. Experimental factors are water supplied and N addition under natural conditions. The results were showed that the whole growing season net ecosystem CO2 exchange (NEE), the total ecosystem productivity (GEP), the value of ecosystem respiration (ER) were tested increased at first and then decreased, and in the growing season (August) reached at maximum. Under N, W treatments NEE has been increased, but the other treatments NEE has been reduced. Under N, WN treatments ER has been increased, but the other treatments ER has been reduced. Under N, W, WN treatments GEP has been increased, but the other treatments GEP has been reduced. NEE, ER, GEP reached at maximum at the N treatment. The changing global climate and the predicted increasing frequency of extreme weather in Inner Mongolia in the coming years may result in changes in resource availabilities. Therefore, our research results have important implications for better managing grassland in Inner Mongolia.
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