水分梯度上放牧对内蒙古主要草原群落功能群多样性与生产力关系的影响

Effect of grazing on the plant functional group diversity and community biomass and their relationship along a precipitation gradient in Inner Mongolia Steppe

应用样线法对放牧对内蒙古草原沿水分梯度分布的主要植物群落:小针茅(Stipaklemenzii)群落、大针茅(Stipagrandis)群落、羊草(Leymuschinensis)群落和羊草杂类草群落多样性、生产力以及两者关系的影响进行了研究,结果表明,除羊草杂类草群落外,物种多样性、生活型多样性和水分生态类型多样性随放牧强度的加大而降低,但适度放牧增加了羊草杂类草群落的上述多样性指标。群落地上现存量一般随放牧强度的增大而下降,但小针茅群落反之,主要与1年生植物猪毛菜(Salsolacollina)的生物量迅速增加有关。除羊草群落外,其他群落0～10cm地下生物量随放牧强度的变化不显著;放牧显著降低羊草群落和羊草杂类草群落0～30cm地下生物量。多样性和生产力间的关系在群落水平上的趋势是不同的,但放牧影响下内蒙古草原4种群落多样性与生产力总体而言呈线性增加关系;同时两者之间的关系还和采用哪种多样性指标和生产力指标有关,用水分生态类型多样性比物种多样性更能反映与地上地下总生产力间的关系,得到放牧影响下内蒙古草原植物群落地上地下总生物量与水分生态类型多样性的回归方程。

There has been a rapidly increasing interest in the effect of species diversity or functional group diversity on ecosystem productivity. In order to search a general diversity-productivity pattern and find the mechanisms underlying the pattern, ecologists have undertaken many empirical studies. But the diversity-productivity connection still remains unclear. The main purpose of this study was to examine the effect of plant species diversity and functional group diversity on productivity of different communities in the Inner Mongolia grazing steppe. Four typical plant communities Stipa klemenzii, Stipa grandis, Leymus chinensis and Leymus chinensis ＋ forbs, were chosen along a precipitation gradient. In each community 2 - 3 grazing intensities were chosen, a total of ten experimental sites were selected. Ahoveground hiomass by species was sampled on each site using twenty 1.0 m × 1.0 m quadrats. Belowground biomass was sampled in three layers 0-10 cm, 10-20 cm, 20-30 cm using ten 25 cm × 25 cm quadrats. The Shannon-Wiener index was used as a measurement of species diversity and functional group diversity. The plant species of the ten sites were classified into functional groups based on differences in life form, water requirements and photosynthetic pathway. These factors influence their performance, resource requirements, tolerance to water stress and seasonal growth. The life form functional groups were shrubs and semi-shrubs, perennial bunch grasses, perennial rhizome grasses, perennial carexes, and perennial forbs and annuals and biennials. The water ecological functional groups were： xerophytes, xeromesophytes, mesoxerophytes and mesophytes. The photosynthetic pathway functional groups were warm season plants and cool season plants. The life form functional groups responded differently to grazing intensity in different plant communities： in the Stipa klemenzii community, perennial bunch grasses decreased while annuals and biennials increased with increased grazing intensity, in the Stipa grandis and Leymus chinensis communities, the perennial bunch grasses and rhizome grasses decreased while the perennial forbs increased with increased grazing intensity and in Leymus chinensis ＋ forbs community, perennial rhizome grasses decreased while perennial bunch grasses increased when grazing intensity increased from un-grazed to moderate grazing. Grazing decreased cool season plants anti non-xeropytes while the warm season plants increased. Results on the effects of grazing by sheep on species and functional group dix＇ersity have not been consistent across all plant communities： species diversity, diversities of life forms and water ecological types decreased as grazing intensity increased except in the Leymus chinensis ＋ forbs community. Grazing reduced the aboveground biomass of the communities except in the Stipa klemenzii community. In this case the annual warm season plant, Salsola collina, became the absolute dominant species in the community. There was no significant change in 0~10 cm belowground biomass except in the Leymus chinensis community and grazing reduced the 0 - 30 cm belowground biomass in the Leymus chinensis and Leymus chinensis ＋ forbs communities. The relationship between diversity and biomass in Inner Mongolia grazing steppe can be described.