| Due easily to enter into environment and a long residual period, atrazine is a widely used herbicide, which easily causes phytotoxicity for some sensitive succession crops, such as wheat, soybean, rice and so that is a typical organic pollutant. This pollutant has eluviation in soil, and is easy to be leached to deeper soil or follow surface runoff into rivers and lakes, polluting groundwater and surface water. The submerged plants which grow on sediments of shallow lake and stay themselves in overlying water, not only are poisoned by residues of atrazine, but also can accelerate the degradation of atrazine under certain conditions. Disclosing the interaction effect of atrazine and submerged plant and its related mechanism, has important significance for the bioremediation of atrazine polluted water bodies.This article selected two kinds of submerged plants:monocotyledonous submerged plant Potamogeton crispus L, and dicotyledonous submerged plant Myriophyllum spicatum L. for the hydroponic experiments in the sediment-overlying water system. The aim of this study was to investigate the influence of the selected submerged plants on atrazine degradation and the mechanism through determination of maximum adsorption capacity of atrazine on the selected sediment, the physiological and biochemical index of the submerged plants under treatments of different concentration of atrazine, the degradation dynamic of atrazine under the influence of the submerged plants, and the the most-probable-number of atrazine degrading bacteria. The main results include:1. The atrazine equilibrium adsorption data by Lake Nanhu sediment fit well with Freundlich adsorption isotherm equation, and combined with prepared pot experiment, choosen the atrazine concentration in sediment is0.5mg/kg and the following as the concentration for the experiment, which provides basis for the following hydroponic experiment.2. The changes of fresh weight, chlorophyll content, MDA, POD index of the selected submerged plants under0.10mg/kg,0.25mg/kg and0.50mg/kg atrazine treatments indicate that, in the whole concentration range, atrazine has low toxicity on Potamogeton crispus L, and low influence on physiological and biochemical index except for its chlorophyll content under0.50mg/kg treatment; but for Myriophyllum spicatum L, atrazine has notable influence on its chlorophyll and MDA content, and POD activity under0.50mg/kg treatment.3. Residual atrazine contents in overlying water and sediments during different growth periods of the submerged plants show that, for Potamogeton crispus L, after90days’growth, under0.10mg/kg,0.25mg/kg,0.50mg/kg atrazine treatments, atrazine degradation rate in overlying water was97.9%,97.2%and96.3%, and was97.1%,95.0%and95.1%in rhizophere sediments, was96.3%,94.9%and94.0%in non-rhizosphere sediments, respectively. For Myriophyllum spicatum L. at the same time and same treatments, atrazine degradation rate in overlying water was97.8%,96.8%and94.8%,96.5%,95.7%and94.5%in rhizosphere sediments, and95.8%,95.4%and94.0%in non-rhizosphere sediments, respectively. For the control with no plant growth, atrazine degradation rate in overlying water was98.5%,97.4%and96.9%, and was97.3%,95.8%and95.2%in sediments, respectively. By comparison of the atrazine degradation rate in the overlying water and sediments, it can be found that atrazine degradation rate was the highest for the control, this suggests that the selected submerged plants are not able to stimulate the degradation of atrazine, on the contrary, they have inhibitory in which the inhibitory effect of Myriophyllum spicatum L is more obvious.4. The most-probable-number of atrazine degradation bacteria were determined to explain the influence of the selected submerged plants on atrazine degradation from the microorganism, the results show that the selected submerged plants can inhibit the growth of atrazine degradation bacteria in rhizosphere sediments. |
