SUBMERGED MACROPHYTE SEED BANK IN A MEDITERRANEAN TEMPORARY MARSH - ABUNDANCE AND RELATIONSHIP WITH ESTABLISHED VEGETATION

The abundance and composition of the submerged macrophyte seed bank in the Donana marsh (southwestern Spain) was evaluated to assess its rel ationship with the overlying vegetation. The results obtained demonstr ate the existence of a dense seed-bank, both in terms of the number of seeds and their biomass, which represented about 10 % (5 % for angios perms and > 20 % for Charophyta) of the total plant biomass, which ens ures the maintenance of the annual submerged macrophyte populations of the seasonally inundated Donana marsh. Seed bank and established vege tation were coupled, as reflected in the existence of significant corr elations between their structure and abundance. This coupling was lack ing for Charophyta, whose oospores are widespread and abundant across the marsh, even at locations where they are absent, or rare, in the es tablished vegetation. These differences between the seed bank of annua l angiosperms and Charophyta appear to reflect, in part, structural di fferences between angiosperm seeds and Charophyta oospores, with impor tant ecological consequences. An important aspect of these differences is the allocation of Charophyta reproductive effort to many small pro pagules lacking embryo storage, compared to those of angiosperms, whic h ensures their efficient dispersal and numerical abundance in the see d bank.