The biomass is a quantitative descriptor of the growth form of submerged macrophytes. Biomass indicates an important ecological characteristic of macrophytes communities because it is closely related to the influence of plants on the extinction of light within stands. Biomass also influences the communities of benthic invertebrates in vegetated sediment and fish abundance in weed beds. Biomass reflects the growth form of the dominant species in the stand, because stands of species with similar growth forms also have similar biomass. Biomass has important implications for light capture and light competition with neighboring plants. Thus, biomass should be a useful index in the quantitative analysis of submerged macrophytes community structure.
Potamogeton malaianus Miq. is one of the dominant species in Lake Taihu, whose ecosystem has been deteriorating due to the increasing amount of pollutants discharged into the water body since the 1980s. P. malaianus forms a monotypic stand in many water zones in Lake Taihu. In order to have a better understanding of the biomass of P. malaianus and why it is becoming the dominant species in Lake Taihu, two investigations of the biomass of P. malaianus, along with water quality and sediment, were performed in different sites in May and October, 2006. The results show that, (1)The biomass of P. malaianus varies greatly (526-4843 g m^-2 )in the different sites and Bleaf > Broot > Bstem per individual P. malaianus. The Bleaf is 55%~80% per individual P. malaianus. (2) Stem height and biomass are directly proportional to water depth. P. malaianus can regulate its biomass via the self thinning effect to meet the resource supply and light availability. (3) There is positive correlation between biomass and TN content in water. N-P ratio in different component is all beyond 16, ranging from 16.92 to 59.88. The mean value of N-P ratio of the leaf is 42.33. Phosphorous is the main indirect influential factor on the growth of P. malaianus. (4) Water transparency is the main limiting factor of the survival ability and biomass variation of P. malaianus in Lake Taihu. The high phenotypic plasticity enhances the survival ability of P.malaianus in the adverse transparency environment. (5)The sediment depth shows a prominent effect on the distribution and BD of P. malaianus. The decomposed P. malaianus contributes to the organic matter in sediment and releases toxins to limit plant growth. The morphological adaptive ability of the structure of P. malaianus helps the plant to survive the adverse effect. Fishing activities and water transportation cause great damage to the BD of P. malaianus.