In recent years, ecological restoration of eutrophic lakes has been highlighted, and the restoration of aquatic macrophytes is considered to be a means of successful ecological restoration. However, the restored macrophytes are frequently found to be difficult to survive or easy to be dead in the summer. Underwater light deficiency is generally considered to be the main reason for decline and for restoration failure of aquatic macrophytes. The mechanism causing the light deficiency is also different among lakes due to their physical, chemical and biological difference. Especially in eutrophic lakes, the physical, chemical and biological indexes in the waters detected are very different from those in lakes of lower trophic levels. Physiological and biochemical indexes of aquatic macrophytes change in response to environmental variations. According to the response patterns reported in other experimental studies of macrophytes, the present study chose Meiliang Bay of Lake Taihu where cyanobacteria blooms every year and the survival of restored macrophytes was low, and the enclosure in hypereutrophic Shuiguohu Bay of Lake Donghu, (nowithout cyanobacteria blooms, where E. nutalli was always dead in the summer after restoration, as investigative region of macrophytes. We monitored annual and early summer changes in and related environmental parameters, and physiological and biochemical indexes of 5 macrophytes in Meiliang Bay and E.nutalli in Shuiguohu Bay, respectively. The main results and conclusions are as follows:
Annual dynamics of physiological and biochemical indexes of 7 aquatic macrophytes in the enutrophic waters showed that the SC contents changed from 5 to 105 mg/(g •DW), the FAA contents changed from 1.9 to 15.8 mg/(g •DW), the protein contents changed from 0.7 to 9.2 mg/(g •FW), and the SOD activity changed from 12 to 641 U /( mg•Pr) in the 5 aquatic macrophytes. During the presence of cyanobacteria bloom, the SOD activity of the five aquatic macrophytes reached the peak while their protein contents fell to the lowest. In this period, the soluble sugar content of most macrophytes increased while their amino acid content decreased.
E. nutallii restored in eutrophic water was frequently found dead in summer. This may be due to exaggerating of environmental stresses with the heavy raining weather in early summer in Wuhan. We investigated the dynamics of environment parameters,and growth and biochemical indices of E. nutrallii at 2 days intervals from June 7 to July 13, 2004. Results showed that increased water depth, decreased DO and PAR, increased wave were related to growth inhibition. Increased tissue NH4+ under light deficiency caused the increase of SOD. Decrease of amino acids, soluble protein and soluble carbohydrate contents under light deficiency might be due to the decrease of photosynthesis, which enhanced decomposition and inhibited assimilation；Increased POD was observed with injury of shoots and roots. Dynamics of the investigated parameters showed that injury, ammonia accumulation and reserve consumption of E. nutallii had impacted the growth condition significantly, which further decreased the resistance of the plant to environmental stresses such as high temperature and algae blooming after the rainy season in midsummer.