中文摘要：

降水量引起草原群落生产力的年际间波动,而典型草原系统又维持着相对稳定的生产力,其稳定的机制如何,是目前草原生态研究急需探讨的问题。文中研究根据中国北方广泛分布的羊草大针茅草原24年的定点监测数据,分析草原地上生物量与研究区10类气候因子的回归关系,结果表明4-8月的累计降水量对草原生物量的影响最大,降水量仅能解释生物量的13%左右。草原地上生物量随降水量年际间变动而波动,其波动幅度不如降水量波动幅度大,说明群落生物量具有相对稳定性。进一步分析24年样方中出现77种植物的相对生物量,结果表明相对生物量大的物种,其生物量的变异系数小,就是说草原群落优势种年际间的生产力波动性较小,这有利于维持系统的稳定性;相关分析显示31种植物之间存在着负相关,这些种之间可能存在着生物量的补偿性。通过分析这些植物种间的补偿性,可以看出优势种与亚优势种,优势种与其他非优势种,非优势种之间均存在着补偿性,这表明在草原生态系统中,当一个物种由于水分的限制使其生产力低于其平水年的生产力时,其他物种的生产力相对的增多,弥补了由于该物种生产力波动引起的群落总生产力的波动,从而相应地维持了草原生态系统的相对稳定性。总而言之,典型草原生物量随降水量的波动性较强,而其生产力能够长期维持相对稳定性依赖于群落中植物种类之间的补偿性。

英文摘要：

Precipitation was a main climatic factor for grassland biomass of the typical steppe in semi-arid region of China,and it frequently caused the fluctuation of grassland productivity between deferent years,but over a long period of time,the grassland ecosystem could maintain the relative stable productivity,and hence,it was imperative to study the mechanism of stability existed in the grassland productivity.Here this paper presented the results of a long-term（1980-2004） study observed in the natural steppe communities of the Northern China,and it was a kind of the rhizome-grass-dominated communities.Multiple regressions were used to examine if the aboveground community biomass was correlative with several climatic variables： accumulative precipitation from last October to April,accumulative precipitation from last October to May,accumulative precipitation from last October to July,accumulative precipitation from last October to current August,accumulative precipitation from last October to September,January-July accumulative precipitation,April-July accumulative precipitation,April-August accumulative precipitation,April-September accumulative precipitation,annual precipitation.For the Leymus chinensis and Stipa grandis grassland,April-August precipitation was a relative significant variable in multiple regressions,and could explain around 13% of the variation in grassland biomass.Furthermore,the extent of interannual fluctuation of community biomass was not sharp as to precipitation change,and in some extent,it meant that a kind of relative stability was maintained in community productivity.Therefore,the study continually compared the coefficient of variation（CV） between the 77-species biomass during 24 years,and it showed that species with higher relative biomass tended to have lower CV,thus the relative stability of grassland ecosystem was appeared due to the small CV of dominant species.Hypothesized that there was the compensatory mechanisms in the grassland ecosystem for resisting its changing enviro