Effects of the grazing systems on germinable soil seed bank of desert steppe

We studied a soil seed bank in the Stipa breviflora desert steppe under three grassland management systems,namely continuous grazing,rotational grazing,and no grazing,from 1999 until 2007.The germinable seed bank species in rotational,continuous and no grazing were 11,9 and 8 species,respectively.Rotational grazing increased the number of seed bank plant species and perennial grasses.The density of germinal soil seed bank was significantly higher in the enclosed area(19,533.33 seeds/m 2) than those in rotational(3,233.33 seeds/m 2) and continuous grazing areas(2,553.60 seeds/m 2).The vertical distribution of the soil seed bank had a similar trend:75.06%-83.19% of the seeds are distributed in the top 0-5 cm soil layer,14.16%-21.68% in the 5-10 cm layer,and 2.65%-4.95% in the 10-15 cm layer,which varied between the grazing treatments.Density of the soil seed bank was significantly higher in the enclosed area,and there was no significant difference between rotational and continuous grazing.The Margalef and Shannon-Wiener indices for the soil seed bank were higher for rotational grazing treatment than for continuous grazing.The Sorensen’s similarity index for the soil seed bank between the enclosed and rotational grazing areas reached 0.857.