The effect of successional stage and salinity on the vertical distribution of seeds in salt-marsh soils

Seed bank density and similarity between seed bank and above-ground vegetation along depth were compared between two salt-marshes different in age. In addition, the effect of salinity on the variation in seed bank density and similarity between seed bank and aboveground vegetation along depth was investigated. The study was conducted in an euhaline saltmarsh that contained both old and newly created habitats. In addition, two other old saltmarshes were selected to study the effect of salinity on the distribution pattern of seed bank and similarity between seed bank and above-ground vegetation at different soil depths. One of them was mesohaline, the other euhaline.Ten plots of 2m × 2m were situated in the new salt-marsh (existing since 2002) and 80 plots in the three old salt-marshes. Soil samples were collected at three different depths (0- 5cm, 5-10cm and 10-15cm) in spring 2006. After washing by fresh water, the soil samples were spread in the greenhouse to allow viable seeds to germinate. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Aboveground vegetation composition was determined during the growing season in all plots. Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, age and salinity of the salt-marsh on density and similarity between seed bank and above-ground vegetation.The results showed that seed density decreased with depth in all salt-marshes irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt-marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the above-ground vegetation of the old salt-marsh.The characteristics of the seed bank of a mesohaline salt-marsh were found not to be fundamentally different from that of both euhaline salt-marshes