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

We studied the soil seed bank of Stipa breviflora desert steppe at three sites with different grazing systems,namely a continuously grazed area,a rotationally grazed area including eight rotational paddock,and an enclosed area which had been enclosed since 1999.The germinable seed bank species in the rotationally grazed area,the continuously grazed area and the enclosed area were 11,9 and 8 species respectively.Rotational grazing increased germinable seed bank plant species of grassland community and perennial grasses.The density of soil seed bank per square meter at the enclosed area(19 533.33±10 552.83 seeds\5m-2) was significantly higher than those at the rotationally grazed area(3 233.33±524.21 seeds\5m-2) and at the continuously grazed area(2 553.60±2 152.48 seeds\5m-2),but the difference between the rotationally grazed area and the continuously grazed area was not significant.The vertical distribution of germinable soil seed bank at different areas had a same tendency,and 75.06%~83.19% of seed was distributed in the soil horizon of 0~5 cm,14.16%~21.68% was distributed in the soil horizon of 5~10 cm,0~6.10% was distributed in the soil horizon of 10~15 cm.The density of germinable soil seed bank at each soil horizon in enclosed area was significantly higher than those in rotationally and continuously grazed area,but there was not significant difference between the rotationally grazed area and the continuously grazed area.Margalef index and Shannon-Wiener index of germinable soil seed bank in rotationally grazed area were higher than that in continuously grazed area.The Sorensen's similarity index of germinable soil seed bank between the enclosed area and the rotationally grazing area was the highest,which was 0.857.