THE PHOTOSYNTHETIC CHARACTERISTICS OF FIVE SUBMERGED AQUATIC PLANTS

With iodimetric analysis,the variations of the concentration of O2 in the water were measured to investigate the variations of photosynthesis and respiration of submersed aquatic plants including Myriophyllum spicatum,Ceratophyllum demersum,Vallisneria gigantean,Potamogeton crispus and Hydrilla verticillata,and to compare photosynthetic productivity and photosynthetic characteristics. Light compensation points of Myriophyllum,Ceratophyllum,Vallisneria,Potamogeton and Hydrilla occurred at 27.5,24.4,9.4,20.0 and 15.8 μmol/m2/s,respectively. Light saturation points were about 1000,1000,200,500 and 500 μmol/m2/s,respectively.Ranks of species in photosynthetic productivity were variable under different light intensity.Under 30μmol/m2/s light intensity the photosynthetic rate of Hydrilla was the highest,Vallisneria was the second,Potamogeton was the lowest. Under 200μmol/m2/s the photosynthetic rate of Hydrilla was the highest,Potamogeton was the second,Vallisneria was the lowest. Under 1 800μmol/m2/s the photosynthetic rate of Ceratophyllum was the highest,Myriophyllum was the second,Vallisneria was the lowest. Photosynthesis of 5 submersed aquatic plants were inhibited by high-light. Under 1 800μmol/m2·s light intensity photosynthetic rates of Myriophyllum,Ceratophyllum,Vallisneria,Potamogeton and Hydrilla were 26.3%,28.3%,80.8%,42.3%and 42.2%lower respectively than light saturated photosynthetic rates of them. The bottom of stalk of Myriophyllum,Ceratophyllum,Potamogeton and Hydrilla was no leaves,their photosynthesis was not or a little,and was non-photosynthetic stalk. Dark respiratory rates of non-photosynthesis stalks were about 19.1% to 55.1% of photosynthetic stalks’.It indicated that energy consumption of non-photosynthetic stalks was less than photosynthetic ones. Submersed aquatic plants with non-photosynthetic stalks can live in deeper water than those without non-photosynthetic stalks. Vallisneria had the lowest light requirement of the species examined. It could adapte to low light and could not tolerate high-light;Myriophyllum and Ceratophyllum adapted to high-light,they were dominant species in surface layer;Potamogeton and Hydrilla had middle light requirement of the 5 species examined,they were dominant species in the middle layer of the water body.