Soil seed bank and its relation with above-ground vegetation along the degraded gradients of alpine meadow

Degradation of alpine meadow may change the composition and size of the soil seed bank, which will impact on the seed bank's capacity for restoration. Four plots were selected to represent the degradation gradients of alpine meadow on Tibetan plateau, namely normal meadow, lightly-degraded meadow, moderately-degraded meadow, and severely-degraded meadow. Soil cores were collected in two seasons, November of 2004 (after seed dispersal) and April of 2005 (before seedling emergence). Soil seed banks were examined by a seedling emergence method. Totals of 56 and 57 species were identified from soil seed bank of four plots in November and April, respectively. The mean size of the soil seed bank on the four plots varied between 2662 and 8026 seeds m−2 in November, and between 3744 and 9773 seeds m−2 in April. The difference in soil seed bank size between the two sampling times (November and April) was not significant within plots. Soil seed banks and above-ground vegetation presented the same trend with vegetation succession across the differently degraded meadows. In all plots, hemicryptophytes accounted for the majority of species and produced the largest number of seeds, of which the majority was weeds. In degraded meadows, the significant increase in weeds (species richness, plant density) changed species composition of soil seed bank and above-ground vegetation along degrading trend. The soil seed bank has important implications for vegetation succession and the restoration of species-diverse alpine meadow on the Tibetan plateau.