The Changes Of Species Abundance Distribution Patterns Of Plant Community With Slope Aspects And Sampling Area In Subalpine Meadow

We studied species abundance distribution patterns along slope aspects and sampling area, estimated the role of common and rare species in maintaining community species diversity in subalpine meadow in Hezuo.Gannan. Five models (including log-series, geometric series, broken stick, overlapping niche and random assortment model) were used to fit species abundance at three leves (community,common and rare species). We fitted species abundance distribution pattern at each slope aspect and sampling area by combining the same level of quadrats.We also evaluated respectively the relative contribution of common and rare species to community species richness along the slope aspects and samples area.Our results showed that:1) In the whole slope level, the order of the five goodness-of-fit for community species is:broken stick> geometric series overlapping niche> random assortment> Log-series. As the slope aspect changed from south-facing to north-facing, the model which best fit the species abundance distribution pattern transit from the geometric series model to the broken stick model.2) The common species abundance can be well fitted by the geometric series model, while none of the five models could fit rare species abundance distribution.3) Common species richness is unchanged, (approximately equel to 20), while rare species number varied from 6 (south-facing) to 29 (north-facing).4) Along the size of sampling area, the order of the five goodness-of-fit for community species is:geometric series model> broken stick model> overlapping niche> random assortment model> Log-series model, geometric series model could well fit species abundance distribution in plant community of all samples area degrees, species number varied from 15 (one of south-facing) to 70 (one of north-facing) along the area gradient. Common species number were unchanged, while rare species increased from 6 (one of south-facing) to 50 (six of north-facing), whether at slope aspect levels or sampling area levels, the increase trend of community species richness were consistent with rare species. Large number of rare species lead to the difference of species abundance distribution pattern.5) Both sample sze and soil moisture content could explain 83.21% of the species richness, the sampling area could explain 14.12% of the species richness and soil moisture content could explain 63.45%. The main reason for difference of species richness is environment heterogeneity caused by the difference of soil water content in the slope aspect. The dominant mechanism in community assembly is deterministic niche partition process.