Persistent soil seed banks along altitudinal gradients in the Qilian Mountains in China and their significance for conservation management

The qualitative and quantitative parameters of persistent soil seed bank, including species composition, seed density, vertical distribution and the relationship of soil seed bank and vegetation, were assessed along an altitudinal gradient in seven communities in shady slope, sunny slope and summit plain of Qilian Mountains. The highest density of soil seed bank of 3946 seeds m(-2) was found in grassland in summit plain, and lowest of 225 seeds m(-2) in the dwarf scrub grassland in shady slope, while the highest numbers of species of 21 species in per sampled area of 962 cm(2) was found in grassland in sunny slope and lowest of 5 species in per sampled area of 962 cm(2) in scrub land in shady slope. Of the species 18% were annuals and 73% perennial herbs, only 1 shrub of Salix gilashanica was recorded. Considerably more seeds were concentrated in the upper layer (0 to 5 cm), and seed density declined by 71.10% in the lower layer (5 to 10 cm). There was a tendency for the soil seed bank to decrease in density with increasing elevation in both shady slope and sunny slope, although this pattern is complicated by the occurrence of different plant communities and species at different altitudes. Sorensen similarity index between soil seed bank and vegetation of the seven habitats was very low, and Picea crassifolia was absent in the soil seed bank despite being a prominent component of the surface vegetation at woodlands; thus, P. crassifolia has no persistent seed bank. It will be important to maintain the existing vegetation in the future management