High abundance of algae and eutrophication were observed in mangrove wetlands and these were estimated to be associated with root exudates of some specific mangrove plants to a certain extent. Root exudates form allelopathic effects from mangroves. The main secondary metabolites of Aegiceras corniculatum had been detected to be organic phenolic acids. Gallic acid had been isolated and identified from A. corniculatum. The half-maximal inhibitory concentration of gallic acid on alge Cyclotella caspia was tested as 15.46 mg/L. The effects on algal cell morphology were mainly shown as elongated cells, with no apparent cell inclusions, such as oil droplets, chloroplast. At a dose of 2 mg/L, gallic acid had a stimulative effect on the specific growth rate of algae on day 3. The contents of malondialdehyde, superoxide dismutase, soluble carbohydrates and chlorophyll a in algal cells showed an overall ＂low promotion and high suppression＂. Our results could provide preliminary and valuable reference on the complex influences of mangroves on microecology and microbial communities in the rhlzosphere system.
Alkylphenols （APs）, the breakdown products of alkylphenol polyethoxylates that are widely used as surfactants, have been proven to exert estrogenic effects. With industrial development, higher concentrations of APs are discharged into aquatic environments. Nonylphenol （NP）, the most noxious AP, is included in the blacklist of several countries. The toxicity of NP to the alga Cyclotella caspia and the biodegradation of NP by C. caspia were studied in the laboratory. The median effective concentration at 96 hr （96 hr EC50 ） of NP for C. caspia was found to be 0.18 mg/L. Five toxicity and three degradation indices were selected for toxicity and biodegradation experiments, respectively, in five or three concentrations of NP set by the 96 hr EC50 of NP. The algal growth rate and chlorophyll a contents decreased as NP concentration increased. The main manifestations of morphological deformity of the cells included volume expansion and the presence of cytoplasmic inclusions （lipid droplets）. The abnormality rate of the cells increased with NP concentration and time, and was 100% at 0.22 and 0.26 mg/L of NP after 192 hr of culture. Superoxide dismutase activity initially increased and then declined at a higher NP toxicity of greater than 0.18 mg/L. After 192 hr of culture, the biodegradation rates of NP by C. caspia with initial concentrations of 0.14, 0.18, and 0.22 mg/L were 37.7%, 31.7%, and 6.5%, respectively. The kinetic equation of C. caspia biodegradation on NP was correlated with algal growth rate and initial NP concentration.
