Buffering effects of the soil seed bank on annual plant community composition after wetland drying

Subalpine peat wetlands are extremely sensitive to global environmental changes and anthropogenic disturbances. Unlike most other biological groups, plant species can possess dormant life-history stages such as the soil seed bank (SSB), which may help plant communities to resist or at least postpone the detrimental impact of disturbance. This study investigates the potential for SSB to achieve this along a soil moisture gradient. Species richness and density of SSB were significantly lower by 31.9% and 47.2% in wetland, and 35.1% and 68.1% in swamp meadow in comparison with steppe meadow, respectively. Soil moisture content did not directly affect the density and species richness of SSB, whilst had indirect effects on density and species richness via affecting vegetation and soil pH. SSB composition was less responsive to soil moisture changes than plant community composition. Furthermore, compositional trends in the annual plant SSB were weaker than in the aboveground vegetation along the soil moisture gradient. The similarity between SSB and vegetation significantly declined with increasing soil moisture content. High SSB diversity and compositional similarity between the vegetation and SSB may provide a potentially important functional buffer against the impact of ongoing moisture changes on plant communities in wetlands. Dormant life-history stages can therefore be important sources of diversity in changing environments. Furthermore, although SSB has low regeneration potential for the aboveground vegetation communities in subalpine peat wetlands, the SSB would still not be a neglected factor for the restoration of propagule diversity after disturbance in wetlands if hydrology is restored.