Soil environmental factors drive seed density across vegetation types on the Tibetan Plateau

Soil seed banks are an important source of seedling recruits in grassland ecosystems, particularly following large-scale disturbance. Nonetheless, the relative importance of above-ground plant communities versus below-ground processes in maintaining these seed banks is poorly understood. Here we collected 1026 soil seed bank samples and sampled 171 aboveground vegetation quadrats in 57 sites representing six distinct grass-dominated vegetation types present at high elevation on the Tibetan Plateau, China. To understand processes affecting seed banks at these sites we examined the associations of soil environmental variables with community composition, density and species richness. We found significant differences in species composition between the seed bank and standing vegetation in each of the vegetation types, whereas soil seed banks were much more similar to each other. Nonetheless, seed bank composition was significantly associated with soil moisture, pH, and available nitrogen (all p < 0.05). Seed density was significantly negatively correlated with soil pH and positively correlated with soil moisture and soil organic matter. Multiple regression analysis showed that for seed bank density a model including pH alone had the lowest AIC value. Soil conditions influence not only seed inputs but also potentially seed survival in the soil, this study present a framework which supply a plausible explanation on effect of soil environment factors (chemical and physical factors) in the formation of species composition of soil seed bank. Future work should isolate the direct and indirect effects of soil chemistry on seed persistence using seed burial experiments.