Inhibitory Mechanism Of Watermelon Peel On Two Kinds Of Filamentous Cyanobacteria And Its Effect On Water Quality In Aquaculture Ponds

Cyanobacterial blooms caused by eutrophication are the one of the main problems to be solved in many lakes and ponds.In order to achieve the dual purposes of the effectiveness and safety of biological materials and the recycling of wastes,two typical filamentous algae,Anabaena flosaquae and Aphanizomenon flosaquae were used to study the inhibition mechanism of watermelon peel from agricultural wastes on these two filamentous cyanobacteria,the possible Allelochemicals of watermelon peel and watermelon peel aqueous extract and the application of cyanobacteria control and water quality control in aquaculture ponds.The main conclusions are as follows.The growth of Anabaena flosaquae was effectively inhibited on watermelon peel aqueous extract.The EPS concentration of Anabaena flosaquae increased significantly to defend against the stress of watermelon peel aqueous extract.The cell viability of Anabaena flosaquae was decreased rapidly after eposure to watermelon peel aqueous extract.The TEM images of Anabaena flosaquae shows cell vacuolation,rupture of cell wall and photosynthetic lamellae,Plasma membrane separation.A significant reduction of chlorophyll A content per cell and photosynthetic efficiency of Anabaena flosaquae.The watermelon peel aqueous extract also had a good growth inhibition effect on Aphanizomenon flosaquae.A gradually reduction of cell number and chlorophyll a content of Anabaena flosaquae after eposure to watermelon peel aqueous extract.Cell viability was significantly decreased and the ultrastructure of cells was severely damaged.Photosynthetic pigments and ROS level of Anabaena flosaquae began to decrease after reaching the peak,and photosynthetic efficiency was also decreased significantly,while the activity of antioxidant enzymes continued to increase.The results of algae toxicity test on the ethanol extract of watermelon peel showedhe compounds with higher polarity had obvious inhibitory effects on Microcystis aeruginose and Anabaena flosaquae,while the weak polarity substances had specific inhibitory activities on Aphanizomenon flosaquae.The results of GC-MS showed that the weak polarity extracts mainly contained palmitic acid,phthalic acid,tocopherol and other compounds.Anabaena flosaquae was mainly inhibited by the organic acid in aqueous extract from watermelon peel,and the growth of Aphanizomenon flosaquae was inhibited by free hydrogen ion from those organic acid.Furthermore,the inhibition on the growth of Microcystis aeruginosa might be due to the combination of the above two effects.The results of field pond experiment showed that the content of chlorophyll a and the bloom of cyanobacteria decreased significantly after adding watermelon peel.In addition to total phosphorus,the addition of watermelon peel did not have a very adverse effect on other water quality parameters in aquaculture ponds.A large amount of organic acids released by watermelon peel can inhibit cyanobacteria,maintain a neutral pH environment,stimulate the growth of green algae,and thus achieve the purpose of controlling cyanobacteria and regulating water quality.