A PRELIMINARY STUDY OF WINTER SEED BANK OF DOMINANT SUBMERGED MACROPHYTES IN LAKE LIANGZI

Seed bank plays an important role in the re-establishment of disturbed vegetations. Soil cores were sampled from substrate of Lake Liangzi in Winter(Feb. 1998), and seed densities(general seed bank, including seed, brood-bud, shoot fragments)of Potamogeton maackianus, P. crispus, Ceratophyllum demersum, Hydrilla verticillata, Vallisneria spiralis and Myriophyllum spicatum, which were the dominant submerged macrophytes of the lake, were estimated by germination methods. The main results are as follows.(1)The seed densities varied in different fegions in Lake Liangzi, being 714.4 seeds/m2 in Manjianghu region and 107.5 seeds/m2 in QianJiang region. But in Zhonghu region and within the palisade region of Lake Liangzi Management, the seed densities were 331.9 seeds/ m2 and 159.3/m2, respectiively.(2)In the community of submerged macrophytes, seed banks of P. maackianus, C. demersum and P. crispus dominated the whole seed bank, with a density of 198.8, 91.7 and 21.4seeds/m2(3)The general seed banks of each plant population had different structure and ratio. For C. demersum,P. crispus, V. spiralis and H. verticillata, the vegetative reproduction units were the most important,but for P. maackianus and M. spicatum, the ratio of seeds was the highest. All of the six studied species could produce seedlings by seeds and vegetative reproduction units,which resulted in an increase in quantity of the populations.(4)The seed banks are usually dormant in Winter(except P. crispus). In Spring, the seed banks began to germinate and the germination Peak occurres from March to April.(5)The submerged macrcphytes seed banks are very complex. Human activities,population size of each plant and fish density can influence greatly the dispersal of seeds and the structure and densities of the seed banks.