Study On The Soil Seed Bank And Typical Shrub And Grass Community Along The Dry-Hot Valley Of Yuanjiang River, Yunnan Province, SW China

As one of most important chararters of plant community, soil seed bank plays a crucial role in the processes of renewal, recovery, sucession and dispersion of vegetation and received several recent attentions. Dry-hot valleys in Yuanjiang River, central south of Yunnan province is one of the typical ecosystems of river valley in SW China. However, to our knowledge, litter study was conducted to investigate the influences of below-ground seed bank on above-ground vegetation and plant assemblages in dry-hot valley of Yuanjiang River. In this thesis, we addressed this issue by assessing and comparing species richness, biodiversity and similarity of below-ground seed bank and above-ground vegetation of shrub and grass community in the dry-hot valleys in the upper, middle and lower areas of Yuanjiang River. The results showed that:1. Seventy-six plant species belonging to 25 families and 64 genera were found in the shrub and grass communities in the dry-hot valley of Yuanjiang River. Most important are Fabaceae, Poaceae, Asteraece and Euphorbiaceae forming prominent families. Perennial grasss speices dominated the shrub and grass community accompanied with some shrub species. Species density in shrub and grass communities did not differed among study sites (Chi-Square=1.888, P=0.756). The population of Heteropogon contortus (Poaceae) is dominant in the herbaceous layers of shrub and grass communities in the hot-dry valleys of Yuanjiang River. However, the subdominated population in herbaceous layers and dominated population in the shrub layers appeared to be variable dependent on the characteristics of environmental conditions. Plant populations were determined by phanerophyte. The number of annuals, chamaephyte and hemicryptophyte did not differ from each other. Geophytes did not been recorded in this study.2. The shrub and grass communities in the study site exhibited an extremely dissimilar level with Jaccard similarity index and Sorensen similarity index reached ranges of 0.043～0.282 and 0.083～0.440. However, we observed high value of similarity index between neighbored plant communities, which indicated the impact of dispersal corridors on dispersal of populations of shrub and grass communities in dry-hot valley of Yuanjiang River. However, the low value of similarity index between distant plant communities indicated the effects of dispersal corridor were influenced by the dispersal distance.3. The abundance, Simpson diversity index, Shannon-Wiener diversity index and Peilow evenness index of herbaceous layer decrease first, and then increase from the upper to the lower of Yuanjiang River. By contrast, the abundance, Simpson biodiversity index, Shannon-Wiener biodiversity and Peilow evenness index of shrub layer occurred from increase to decrease along the Yuanjiang River.4. Thirty-three plant species belonging to 15 families and 32 genera were recorded in the soil seed bank of shrub and grass communities in Yuanjiang River. Most important are Fabaceae, Poaceae, and Asteraece forming the prominent families. The species density of the soil seed bank in shrub and grass communities did not show significantly difference among each other (Chi-Square=12.703, P=0.013). The influences of latitudinal and longtitudinal vectors on the species density of seed bank were minor. The soil seed bank of shrub and grass communities appeared to be determined by herb species with predominance of perennial species and anuual species in terms of species richness and seed species. By constrast, the occupancy of shrub species was lower and played a minor role in the renewal and succession of shrub layer. Overall, the soil seed bank in the shrub and grass communites of dry-hot valley of Yuanjiang River was sustainable in some sense, which would influence the renewal of grass communities in this region.5. The majority of seeds of soil seed bank in shrub and grass communities were concentrated to distribut at 5cm depth of soil layer, while only a small number of seeds distributed in the 5～10,10～15cm depth of soil layer. This indicated the number of seeds in the soil seed bank in the shrub and grass communities in the dry-hot valley of Yuanjiang River decrease with the increasing of soil depth.6. Jaccard similarity index and Sorensen similarity index of soil seed bank in shrub and grass communites in the dry-hot valley of Yuanjiang River reached the ranges of 0.167-0.467 and 0.286-0.636, respetively. The similarity of soil seed bank was in a moderate dissimilar level, which was related to the the high level of heterogeneity of habitat and vegetation among study areas.7. The species richness and diversity coefficient of soil seed bank of the shrub and grass communities in study site successively is Xiangyun County>Honghe County>Xingping County>Yuanyang County>Yuanjiang County. In terms of Peilow evenness index, the order is Honghe County>Xiang Yun County>Xingping County>Yuanjiang county. Generally, the biodiversity index of the soil seed bank of shrub and grass communities in study region showed a relative low value. However, we also observed an idiosyncratics in values of the biodiversity index in soil seed bank among different study sites which was related to heterogeneities in moisture, topographical and elevational conditions in different areas.8. Jaccard similarity index and Sorensen similarity index of below-ground seed bank and above-ground vegetation in the shrub and grass communities of the study region reached ranges of 0.083～0.167 and 0.154～0.286, respectively. The species composition showed a pronounced difference between above-ground vegetation and below-ground seed bank in the study region, which being extremely dissimilar level. Seeds produced by above-ground vegetation contributed little to the below-ground seed bank in the shrub and grass communities.9. The correlation between the density of below-ground seed bank and above-ground vegetation of the shrub and grass communities in the study region did not showed statistical siginificantly (Xiangyun County:P=0.396; Xinping County: P=0.659, Yuanjiang County:P=0.769; Honghe County:P=0.884; Yuanyang County: P=0.156), which indicated that the majority of soil seed bank is not from the above-ground vegetation.