|其他摘要||On the grassland of arid regions, due to the demand of water livestock often round-trip between water point and pasture, thus generates the formation of piosphere. To study the piosphere effects, sampling was carried out based on 6 sampling distance (50m, 100m, 200m, 400m, 800m and 1200m) with eight orientations radiating outward from an artificial water point in desert steppe, Eastern Junggar Basin, Xinjiang. In piosphere, not only the variation characteristics of the plant species composition, quantitative features, value importance, above-ground biomass and diversity, but also the variation characteristics of the species composition, density and diversity of the soil seed bank were studied. Based on these, this study was aimed to determine the relationship between soil seed bank and standing plant. The main results are as follows:
1) With the increase of distance from the water point, the community characteristics varied significantly, suggesting the grazing gradient around the watering point in piosphere.
20 species belonging to 8 families and 13 species belonging to 6 families were recorded in May and October 2014 respectively. With the increase of distance from the watering point, the dominance value of perennials significantly increased, especially for the Seriphidium borotalense, but the dominance value of annuals decreased; the species richness of the community including perennials and annuals decreased; and the vegetation coverage increased, which showed a significant positive correlation with the Seriphidium borotalense. The cover and height of the noxious plant Peganum harmala increased with a declinein the distance from the watering point, which was the reason why there were no gradient changes for the aboveground biomass of the community along with the distances. The improvement of abundance of ruderal annuals and perennials in the vicinity of the watering point indicate that the plant community tends to deterioration with the increase of grazing intensity.
2) In piosphere, the species composition and spatial distribution of soil seed bank were affected by grazing.
There were 17 species belonging to 8 families in soil seed bank. The 8 families are Compositae, Chenopodiaceae, Gramineae, Cruciferae, Leguminosae, Cyperaceae, Zygophyllaceae and Polygonaceae. The species mainly were Compositae and Chenopodiaceae. The number of annual herbs and perennial herbs was 10 and 7 separately. The variation range of the soil seed bank density was 211.5～362.5 seeds﹒m-2, and the lowest density of soil seed bank was found in the closest vicinity of the water point (50m), while the highest was observed in farthest areas (1200m). The species number of the soil seed bank significantly decreased (Spearman correlation analysis, R=-0.74, p<0.01) with distance from water point. Along the same vector, the percentage of the annual herbs increased, while the percentage of the perennial herbs decreased. Since the variation range of the similarity of the soil seed bank coefficient between every two adjacent sampling points was 0.70～0.84, the spatial heterogeneity seemed to be small. The density of soil seed bank significantly increased (ANOVA, df=5, F=15.47, P<0.05) with distance from the water point. The Shannon-Wiener, Margalef and Pielow index of soil seed bank decreased with distance from water point. These results suggested that the number of plant species in soil seed bank was increasing by piosphere effect. This leads the number of ephemeral and ephemeroid plant seeds increasing, while the number of constructive species seeds was decreasing.
3) The similarity between standing vegetation and soil seed bank was high. The nearer to water point was, the higher the similarity was. The variation range of the similarity index between standing vegetation and soil seed bank was 0.36～0.81. The largest number was 0.81 of 50m from water point.|