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

Seed bank density and similarity between above-ground vegetation and seed bank with depth were compared between two adjacent salt marshes that differ in age. In addition, the effect of salinity on the variation in seed bank density and similarity between above-ground vegetation and seed bank with depth was compared between euhaline against mesohaline conditions in three salt marshes.Ten plots of 2 m×2 m were situated in a new salt marsh (existing since 2002) and 80 plots in three old salt marshes. Soil samples were collected at three different depths (0–5, 5–10, 10–15 cm) in spring 2006. Soil seed bank was investigated in germination experiments under greenhouse conditions. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Above-ground 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, salinity and age 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 standing 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