Non-Additive Effects of Inundation Duration and Soil Depth on Seed Banks in a Shoreline Meadow of Poyang Lake in China

Seed banks are fundamentally important components of the wetland ecosystem. Water levels on germination in soil seed banks have been documented in many ecosystems. However, there is a lack of knowledge about water levels on seed banks in freshwater wetlands, especially in those buried by sedimentation. Three burial depths (0-5 cm, 5-10 cm and 10-15 cm) within five water level gradient zones along the elevation in Poyang Lake, Eastern China, were sampled. The seedling-emergence method in a greenhouse under moist conditions and submersion was applied to allow all active seeds to be germinated. The experiment continued over an eight-week period in late spring up to early summer. A total of 7090 seedlings emerged, belonged to 20 families, 36 genera and 49 species. In terms of results, an average active soil seed density of 17,328 +/- 1675 seeds/m2 was found in 0-15 cm in Poyang Lake, and the greatest average seed density was found at 0-5 cm with 7607 +/- 790 seeds/m2, along with 5-10 cm and 10-15 cm with 5419 +/- 589 seeds/m2 and 3855 +/- 790 seeds/m2, respectively. An obvious difference in composition was found in the species composition of the seed bank at different water levels and burial depths. The highest water level and top layer of soil had the highest diversity index, with a Shannon-Wiener value of 2.011. Seed density, species richness and diversity decreased with the water level gradient zone from low elevation to high elevation and burial depth from surface to deepness. However, there was no interaction between inundation duration and burial depth, indicating that the water level fluctuation and sediment buried had a separate impact on the seed bank composition and diversity index. The present findings can be directly applied to the ecosystem conservation of healthy wetlands, and the ecological restoration of devastated and degraded wetlands in Poyang Lake.