金沙江干热河谷山地植被恢复区土壤种子库和地上植被研究

土壤种子库在植物种群动态中起着重要作用。土壤种子库可缓解种群的灭绝过程，保存群落中植物种的表现特征，是植被天然更新的物质基础。通过对金沙江干热河谷山地植被恢复区（包括水平阶、自然坡面、沟底）和未恢复区（包括放牧地）的土壤种子库和地上植被的组成、大小及多样性进行比较研究表明，植被恢复区土壤种子库和地上植被的密度、丰富度、多样性及均匀度均大于未恢复区。恢复区地上生物量要远大于未恢复区。水平阶和各类型间的土壤种子库密度与地上植被密度差异显著。土壤种子库中草本植物占很大比例。孔颖草和扭黄茅是土壤种子库和地上植被的两大优势种，两者的个体数量、重要值及生物量最大。土壤种子库和地上植被有较高的相似性，且随着恢复程度的加深，相似性有增高的趋势；土壤种子库密度和地上植被密度之间关系可以用二次和三次曲线拟合。

Soil seed bank and aboveground vegetation in Jinshajing Hot-Dry River Valley Hillslope vegetation restoration sity

Soil seed bank plays an important role in the composition of different plant communities and especially in their conservation. Although Soil seed bank, aboveground vegetation and their relationship have been the subject of much recent attention, little is known about the size and species composition of soil seed bank and aboveground vegetation in semi-arid hillslope grasslands and understanding of how these components interact to determine the importance of seed banks to regeneration is limited.We assessed the size and species composition of a soil seed bank and aboveground vegetation in an experiment with 36 vegetation quadrats and 108 soil samples in terrace, slope, gully and grazing land that represent a range of habitats within a hillslope grassland in Jinshajing hot-dry river valley of Yunnan. Terrace, slope and gully represent restored site and grazing land typifies unrestored site. We identified 21 taxa in the seed bank with a median of 7 species/m~2 and a median density of 5498 seeds/m~2, while in aboveground vegetation, 19 species were observed with a median of 6 species/m~2 and a median density of 1088 plants/m~2. Both seed bank density and aboveground vegetation density among grazing land, gully, slope and terrace differed significantly. There was an absolutely high proportion of herbaceous species in the seed bank and aboveground vegetation. Gramineae predominated over both seed bank and vegetation. The most frequent seeds and plants were Bothriochloa pertusa (L.) A. Camus and Heteropogon contortus (L.) Beauv that had the highest individual number, importance value and biomass. In the seed bank, the seeds of Bothriochloa pertusa (L.) A. Camus and Heteropogon contortus (L.) Beauv accounted for 50.68% and for 33.10% of the total seeds respectively. In aboveground vegetation, the individual number of Bothriochloa pertusa (L.) A. Camus accounted for 55.66% of the total and Heteropogon contortus (L.) Beauv accounted for 29.86%. The biomass of Bothriochloa pertusa (L.) A. Camus and Heteropogon contortus (L.) Beauv. accounted for more than 70% of total, reaching 206.71 g/m~2 and 147.76 g/m~2 respectively. Bothriochloa pertusa (L.) A. Camus and Heteropogon contortus (L.) Beauv had the highest importance value of 193.01 and 159.99 respectively.Density, biomass, species richness, species diversity and evenness were the highest in terrace while those in grazing land were the lowest. Similarities between the seed bank and aboveground vegetation were moderately high and not very different among slope, gully and terrace, except for grazing land, tending to increase when restorative stage progressed. This result contrasts with some other studies where the seed bank contributes very little to the seedling flora and vegetative growth clearly overwhelms sexual reproduction. The hypothesis about significant functional correlation between soil seed bank density and aboveground vegetation density is conformed. Correlation between soil seed bank density and aboveground vegetation density can be described as quadratic and cubic curves. The strong similarity between vegetation and the seed bank is attributed to the great proportion of the species Bothriochloa pertusa (L.) A. Camus and Heteropogon contortus (L.) Beauv. that are seed-profusive and whose seeds have a significant viability in the ground. The high density, biomass, species richness, species diversity and evenness of the reclaimed site is related to the sufficiency of heat and water supplies for species establishment and growing in the site, which partly reflects our effective efforts on the hillslope grassland restoration. We believe that our vegetation restoration efforts have altered the microhabitat conditions of the site and provided a favorable habitat for species to establish and grow.