Role of the Soil Seed Bank during Succession in a Subalpine Meadow on the Tibetan Plateau

We studied the seed bank of abandoned Fields in four Successional stages (habitat A: I year; habitat B: 10 years; habitat C: 20 years; and habitat D: mature meadow) in eastern Tibetan Plateau. The seed density in seed banks decreased with successional age, but species richness and diversity increased, and the highest species diversity and species richness appeared in habitat C. Similarity between the seed bank and vegetation decreased gradually with succession in the whole. The vegetation is more similar to the seed bank in the shallow layer than to the seed bank in the deeper soil, which shows that the vegetation contributes less to the seed batik as soil depth increases. The seed bank was mainly composed of First Successional species during the whole successional range. Species of the later successional stages contributed little to the seed batik. Most of species from early successional stage produced longer-lived seeds, which stayed viable in the soil for a long period (more than 20 years). Hypotheses about changes in seed bank during Succession, predicting decreasing species richness and seed diversity, were not confirmed. The hypothesis that density of buried seeds declined during Succession was confirmed. We conclude that seed bank plays an important role on vegetation in the early Succession stage. In the later Succession stages, seed bank's role becomes weaker and weaker, and which likely relies on vegetative reproduction and dispersal.