中文摘要：

通过多年围封和放牧2个样地上3个水分梯度的野外试验,以试验区优势种克氏针茅和羊草2个物种及群落为研究对象,分析了水分适宜条件下牧草的生长特性和水分胁迫、放牧等环境因子的影响。结果表明：（1）水分适宜条件下针茅、羊草的最大高度和生物量分别是87.9cm、40.3cm和280g/m2、54.2g/m2,群落的最大生物量、盖度和LA（I叶面积指数）分别是467.6g/m2、91%和2.7;（2）物种高度、针茅和群落地上生物量均符合Logistic生长模型,羊草地上生物量生长曲线S型特征不明显;群落盖度和LAI分别用二项式和三项式拟合效果较好（;3）水分胁迫对草原植被生长有明显的负效应,并随干旱程度的加重而增大;与高度相比,生物量对水分胁迫的响应更强烈,羊草对水分的敏感性大于针茅;在土壤相对湿度40%~50%时,群落最大生物量和LAI降低近50%,盖度减少30%多。水分充足时,针茅达到最佳生长状态所需要的热量为〉0℃积温2500~2700℃（;4）放牧样地群落和物种的生长特征除羊草的地上生物量外,都优于围封样地,放牧样地羊草生物量和单位面积株茎数比围封样地少25%和66.8%。

英文摘要：

This study was mainly done on two dominant species,Stipa krylovii and Leymus chinensis,and on community of Xilinguole typical steppe in Inner Mongolia.The field experiment was carried on two kinds of plots,which while ones of them were enclosed and not grazed for many years,and the others were kept on grazing.With setting treatment of experiment on three water gradients,the growth characteristics of grass under the appropriate water conditions,effects of water stress,and impact of grazing and other environmental factors were analyzed in the study.The results of research showed that： （1） Under appropriate water conditions,height and biomass maximum of Stipa krylovii and Leymus chinensis were 87.9 cm,40.3 cm ,280 g/m 2 and 54.2 g/m 2 ,respectively;the largest biomass,cover-degree and LAI （leaf area index） of community were 467.6 g/m 2 ,91% and 2.7.（2） height of a species,aboveground biomass of Stipa krylovii and community were in line with Logistic growth model,while the growing curve of aboveground biomass of Leymus chinensis not manifested obvious S-type characteristics.And binomial and trinomial fitting were good in fitting analysis for cover-degree and LAI of community.（3） Water stress produced obvious negative effects on the grassland vegetation,and it showed worse gradually with increase of drought severity;the biomass response to water stress was stronger than to height,and water sensitivity of Leymus chinensis was greater than of Stipa krylovii ;with the soil relative humidity dropping on 40%-50% ,the largest biomass and LAI of community reduced nearly 50% ,and 30% reduced on community coverage.When water was sufficient,2500-2700 ℃ was the accumulated temperature （0℃ ） for best growth of Stipa krylovii.（4） Except for aboveground biomass of Leymus chinensis,the growth characteristics of communities and species on grazing plots were better than the enclosed plots.With regard to biomass and stem number of Leymus chinensis on per unit area in grazing plots,they were respectively le