Different response of transient and persistent seed bank of alpine wetland to grazing disturbance on the Tibetan Plateau

Background: With increased grazing disturbance of wetlands, soil moisture decreases, which could have an effect on the seed bank. The seed bank is a crucial resource for vegetation restoration; however, the effects of grazing disturbance on density and richness of seed banks and consequences on restoration of degraded wetlands are unclear. Methods: We selected six alpine wetlands along a degradation gradient on the Tibetan Plateau for study. The structural equation model was used to explore the direct and indirect effects of soil moisture on transient and persistent seed banks through soil physicochemical factors and vegetation. Non-metric multidimensional scaling was used to explore the role of seed banks in alpine wetland vegetation regeneration. Results: A decrease in soil moisture directly increased richness and density of the transient seed bank. However, decreased soil moisture indirectly decreased density of transient and increased richness and density of the persistent seed bank though soil pH and richness and abundance of vegetation. The similarity between the seed bank and vegetation increased with wetland degradation. Slope of the Bray-Curtis dissimilarity between transient seed bank and vegetation was higher than that for the persistent seed bank and vegetation. Conclusions: Transient seed banks remained almost constant under grazing disturbance, which favours persistent seed bank formation. Transient and persistent seed banks were determined by aboveground vegetation and soil environment, respectively. Seed banks provide strong resistance and resilience to degradation of wetland ecosystems, while persistent seed banks play a more important role than transient seed banks in restoration of degraded alpine wetlands.