刈割和氮添加对松嫩平原羊草草原碳固持的影响

Effects of mowing and nitrogen addition on carbon sequestration of Leymus chinensis grasslands in the Songnen Plain,Northeast China

最近30年来,碳固持作为陆地生态系统的重要生态功能受到前所未有的关注。草原是全球面积最大的陆地生态系统类型,割草和放牧是中国草原的最主要利用方式,同时氮沉降是草原生态系统面临的重要全球变化因子,然而它们对草原生态系统碳固持的影响尚未有一致的结论。本研究在松嫩平原羊草草原通过同化箱法观测并对比了刈割和模拟氮沉降条件下生态系统碳通量的变化。结果表明:无论从季节动态还是日动态来看,氮添加处理的净生态系统气体交换量(NEE)、总生态系统呼吸(TER)和总生态系统生产力(GEP)总体上均高于对照,而刈割处理的NEE、TER和GEP均低于对照;就土壤呼吸而言,各处理间无显著差异;整个生长季对照、刈割和氮添加处理累计碳释放量分别为107.8、285.2和102.9 g·m^(-2)·a^(-1);由此看来,整个实验区域是碳源,氮素添加可以在一定程度上减弱草原的碳源作用,且有向碳汇转变的趋势,而高频次和高强度刈割加重了草原的碳源作用。建议在生产实践中对草原实行轻度放牧和施肥管理,既能加强草原生态系统的生产功能,又能增加以碳固持为主的生态功能,从而实现草原生态系统的可持续利用。

Carbon sequestration, as an important ecological function of terrestrial ecosystems is receiving unprecedented attention during the past 30 years. Grassland is the largest terrestrial biome in the world, being utilized primarily by the means of mowing and grazing, and confronted with nitrogen deposition, which is one of the global change factors. However, there is no consen- sus on the effects of these factors on carbon sequestration of grassland ecosystems so far. Using static chamber method, we observed and compared the changes of carbon flux of Leymus chinensis grassland ecosystem under mowing and simulated nitrogen deposition in Songnen Plain, and found that net ecosystem exchange, total ecosystem respiration, and gross ecosystem productivity under nitrogen addition are higher than under the control, while those under mowing conditions are lower than under the control. No difference was found in soil respiration among the three treat- ments. During the whole growing season, the cumulative C02 emissions of control, mowing and nitrogen addition treatments were estimated as 107.8,285.2 and 102.9 g · m-2 ·a-1, respective- ly. Therefore, we conclude that the investigated grassland ecosystem was carbon source, the strength of which was weakened by nitrogen addition, but strengthened by mowing with high fre- quency and intensity. It is suggested that the long- from carbon source to carbon sink. These findings managed by rational grazing and proper fertilization, lasting fertilization may covert the grassland implied that grassland ecosystem should be so that the functions of production and car-bon sequestration can be guaranteed simultaneously, and thus a sustainable use of grassland eco- systems can be realized.