STUDY OF MACROPHYTES NITROGEN AND PHOSPHORUS CONTENTS OF THE SHALLOW LAKES IN THE MIDDLE REACHES OF CHANGJIANG RIVER

Content of tissue nitrogen and phosphorus of aquatic plant is affected by trophic statue of the waters and the plantgrowth condition.Nitrogen and phosphorus contents(N and P) of aquatic plantsof eighteen investigated lakes in the middle reaches of Changjiang River were comparative studied. The results showed that, among all life forms of aquatic plants, the submersedmainly distributed in mesotrophic to mesoeutrophic lakes, while the floating leaved and emergent in lake’ s littoral zone of different trophic levels. N and P contents were highest in the submersed and lowest in the emergent, intermediate in floating leavedplants. All aquatic plants reached or exceeded their least requirements of N and P content for maximum growth N and P contentsof the major submersed and floating leaved plants changed relative to increased trophic levels of the lakes. N and P content of 5aquatic plants showed significant correlations with different N and P species in different growth season. Among the plants of dif2ferent life form, P content of Trapa natans was related significantly to total phosphorus (TP) and total dissolved phosphorus(TDP) in water in the spring and the summer, its N content related to the ammonia (NH42N) in the spring. P content of Pota2mogeton maackianus was related to TP in the spring and to TDP in the summer. N contents of P. maackianus and Myriophyllumspicatum were positive related to total nitrogen (TN) and total dissolved nitrogen (TDN) in the water both in the spring and thesummer, and were negative related in autumn. P contents in shoot and root of Phragmites communis were significantly related toTP and TDP of the water in the summer; N contents in the shoot of P. communis and in Typha latiorlia in spring were relatedto ammonia (NH42N) and nitrite (NO22N). Sumersed and floating leaved plants are more correlatived with the nutrition level oflakes than emergent plants are, so it is better to choose the formers as the indicative species of the pollution degree of water quality.