高寒草甸植物群落中相似性、物种多样性与地上生物量的年际变异性

相似性似说通过物种构成的相似性来解释物种丧失是如何影响生物量的变异性的，但还没有得到检验。本研究通过设置在青藏高原东部地区的高寒草甸植物群落中的74个永久样方．采集3年(1999～2001)植物生长高峰期的群落数据，试图检验物种构成的相似性是如何解释物种多样性对地上生物量年际变异性的影响。结果表明：随着物种丰富度增加，生物量变异性降低；而随着均匀度的增加，生物量的变异性尽管在均匀度中等程度时似乎保持在同一水平，但总体上呈下降趋势；物种构成上的相似性解释了地上生物量变异性的大部分，而且随着物种构成上的相似性的增加，生物量的变异性降低；物种丰富度和均匀度均与物种构成上的相似性没有显著相关关系。这些结果表明：尽管生物多样性的丧失可能不必导致物种丰富群落中物种构成上的相似性，但相似性与地上生物量的变异性的因果联系可能是稳健的．由于本研究是在自然群落中进行的，对物种构成的相似性没有进行直接控制，因此，要深入理解相似性是如何影响生物多样性对生态系统功能变异性的效应的机制，可能还需要直接对物种构成的相似性进行控制的实验研究。

Similarity,Species Diversity,and Interannual Variability in Total Aboveground Biomass in Alpine Meadow Plant Community

The similarity hypothesis may explain how biodiversity loss influences variability in biomass of plant communities but remains untested.We collected data over a three-year period (1999~2001),at the end of July during the peak of plant growing season,from 74 permanent plots in a natural alpine meadow located in the eastern Qinghai Tibetan Plateau.The objective was to test how similarity in species composition can explain the effects of species diversity on interannual variability in total aboveground biomass.Variability in total aboveground biomass per plot,decreased as species richness increased,and it also showed an overall decline as evenness increased although it appeared to stay at about the same level over the intermediate range of evenness.Similarity in species composition explained most of the variability in total aboveground biomass,and increased similarity in species composition reduced interannual variation in total aboveground biomass.Species richness and evenness were unrelated to similarity in species composition.These results indicate that the causal relationship between similarity and variability in total aboveground biomass may be robust,although biodiversity loss may not necessarily lead to decreased similarity in species composition in species-rich communities such as the alpine meadows of the Eastern Tibetan Plateau.Therefore,understanding how similarity influences the effects of biodiversity on variability in ecosystem functioning would require directly manipulated experiments for similarity in species composition.