通过测定不同放牧退化阶段(轻度、中度和重度退化)大针茅典型草原的土壤总有机碳(T OC)、活性有机碳(LOC)和惰性有机碳(ROC)的含量,探究放牧退化过程中大针茅草原土壤总有机碳的组成及其稳定性.同时在群落调查的基础上,采用δ13 C稳定同位素技术阐明大针茅草原在放牧退化过程中群落组成变化对土壤总有机碳的影响.结果表明:(1)不同放牧退化阶段,TOC、LOC、ROC含量均随土层深度的增加而逐渐降低,且中度退化阶段TOC、LOC、ROC含量最高;(2)不同放牧退化阶段惰性碳指数值差异不显著,表明放牧未对大针茅群落土壤总有机碳的稳定性产生影响;(3)不同放牧退化阶段,大针茅草原土壤总有机碳主要来源于C3植物.但是随着退化程度加剧,大针茅草原C3植物的生物量降低,C4植物的生物量增加,C4植物对0～10cm土层土壤总有机碳的贡献增强.综上所述,以上结果可为综合评估长期放牧对大针茅草原土壤碳汇服务功能的影响,以及制定我国温室气体减排增汇策略提供科学依据.

Niche breadths and overlaps of dominant species in restoring succession processes plant community in Huangpuchuan Watershed were measured using a series of indices proposed by Levins,Shannon-Wiener,and ecological significance of niche breadths and overlaps of each community was analyzed.The results show that each typical community is marked absolutely by one species with the largest niche breadth.Dynamic changes of niche breadth in restoring succession are correspondingly related with the changes of populations.Greater niche overlaps will result in more similarities in ecology and resource use of populations, thus leads to a more intense interspecific competition.Competition is a potential dynamic mechanism promoting different plant communities to the climax community in the watershed.

20 dominant species in Huangfuchuan watershed were analysed by X2 test,Pearson's correlation coefficient and Spearman's rank correlation coefficient test.The results indicated that:positive association coefficients of 31 species-pairs for the X2 test were significant(p0.05) or highly significant(p0.01),and negative association coefficients were significant or highly significant in 27 other species-pairs;In Pearson′s correlation coefficient test,16 species-pairs had positive relationship,and 13 species-pairs had negative relationship;In spearman′s rank correlation coefficient test,there were positive relationship between 36 species-pairs and negative relationship between 27 species-pairs.The results showed that dominant species have interspecific relationships and independent distribution pattern.Based on the results,20 species in the community were divided into three ecological groups.

Different land use types of vegetation situation in Wufendigou Model of Huangpuchuan watershed were analysed,using diversity index,richness index,evenness index and community structure,respectively.The results showed that the diversity indexes were in the order of elm woodland(Ulmus pumila)>natural pasture> intermediate brushwood(Caragana intermedia)>simon poplar woodland(Populus simonii)>abandoned land>Chinese pine woodland(Pinus tabuliformis)>seabuckthorn brushwood(Hippophae rhamnoides)>sand willow brushwood(Salix psammophyla)>artificial lawn>arborvitae(Platycladus orientalis).The richness index of intermediate brushwood and evenness index of arborvitae were the highest respectively.The community structure of natural pasture and intermediate brushwood are complex.Considering these indexes and characteristics of community structure,natural pasture,intermediate brushwood and elm woodland should be adopted in the processes of vegetation restoration and reconstruction due to their functions of conserving species diversity.It is necessary to improve the protection of natural grassland and expand the area of intermediate brushwood and elm woodland.