Seasonal dynamics in alpine meadow seed banksalong an altitudinal gradient on the Tibetan Plateau

We studied seasonal dynamics of seed banks along an altitudinal gradient in three alpine meadows on the Tibetan Plateau, as well as seed size distribution relative to depth. Seed bank density and species richness decreased significantly with altitude increase in both April and July. The highest elevations showed highest seed bank depletion. Although species composition of the vegetation changed along the altitudinal gradient, seed bank composition was almost unvaried from April to July. This indicated that seed bank density has an obvious seasonal change but composition does not. We found a low degree of similarity between the species composition of vegetation and of the seed bank along the whole gradient, and this similarity decreased with altitude increase. These suggest that the role of the seed bank decreased gradually with altitude increase. The hypothesis that a species seed bank strategy is an inherited trait was not confirmed because for some species seed bank strategy changed with altitude. We found that persistent seed banks were the most frequent strategy at all three altitudes. Species with persistent seeds tended to have smaller seeds than those with transient seeds only in highest altitude, while the other two altitudes did not show difference. There was no trend in seed size distribution with altitudes and soil depths.