Soil seed bank of Potentilla acaulis community in arid grassland of the upstream of Shiyang River.

Potentilla acaulis is considered as a green barrier to prevent grasslands from further degradation,it has important significance on the direction and improvement of vegetation succession on grasslands,the community degradation mechanism of the soil seed bank can be used to direct grasslands ecology renewing.With field vegetation surveying and laboratory test,the paper chose and identified the seeds from 270 soil samples by adopting physical method,seedling germination and TTC,and then analyzed the soil seed bank of arid grassland's Potentilla acaulis community in upstream of Shiyang River.The results showed as follows:a total of 19 plants belonging to 14 families were found in the soil seed bank,3 species were annual herb and 16 species were perennial herb.There was a significant decreasing tendency of the density of grasses and an increasing tendency of non-edible grass with the increase of Potentilla acaulis's coverage.The number of plant species and the seed density in the shallow soil layer were larger than that in the deep one.The vertical distribution of seed bank's density was presented as the following precedence order: 0-5 cm's10-15 cm's5-10 cm's,the seeds of different functional groups also showed the same distribution pattern.The soil seed bank of Potentilla acaulis is very small,which is accounted for only 2.93% of the total seed bank,its regeneration pathway is inclined to vegetative propagation.The changes of species diversity index and evenness index tend to be uniform.However,the dominance index of the soil seed bank is opposite to the evenness index and diversity index in vegetation gradients.The average similarity index of seed bank and standing vegetation is 0.392.The similarity of species composition of the soil seed bank and vegetation species composition of the surface belongs to a moderate dissimilar level.There is no finding at the seeds of dominant population of primary zonal vegetation,which reflects the irreversibility of degradation mechanism of grassland community.The change of plant species and functional group composition in the study area basically reflects a series of degradation trend of Potentilla acaulis Community,such as community structural simplification and environmental matrix stability weakening.