Effects Of Phalaris Arundinacea Soaking Liquid On The Growth Of Microcystis Aeruginosa And Its Mechanisms Of Lslet Wetland Of Poyang Lake

Poyang Lake is the largest freshwater lake in China.It has a unique landscape of "one flood,one dry line",and the fluctuation of water level is large.In recent years,with the development of social economy,the pollution load discharged into the lake around Poyang Lake has increased,resulting in a downward trend in the water quality of Poyang Lake.Cyanobacteria blooms with Microcystis aeruginosa as dominant algae species often occur in some waters such as Duchang,Junshan Lake,Kangshan Pond,Preparedness Lake and Cuoji Lake.Phalaris arundinacea is one of the dominant plants in Poyang Lake.Its elevation ranges from 9 to 12 m,and it is often submerged in flood season.In order to understand the effect of Poyang Lake beach vegetation on the growth of Microcystis aeruginosa under the condition of alternate submergence and the effect of nutrients and temperature on the Allelopathy of Poyang Lake to inhibit the growth of algae,the results of indoor controlled culture experiments were as follows:1.The extract of Phalaris arundinacea had an effect on the growth of Microcystis aeruginosa,which showed a phenomenon of "low promotion,high inhibition".The growth of Microcystis aeruginosa was promoted when the concentration of the extract was lower than 12 g/L.When the concentration of the extract was 3 g/L,the maximum promoting effect was-158%.With the increase of the concentration of the extract,the inhibitory effect was strengthened.When the concentration of extract was 24 g/L and 48 g/L,the inhibition rates were 52% and 92%,respectively.In Poyang Lake,the current nutrient level and biomass of Phalaris arundinacea are beneficial to algae blooms.2.The allelopathic effect of the extract of Phalaris arundinacea on the growth of Microcystis aeruginosa changed with the nutrient level of the culture medium.When the concentration of the extract was less than 6 g/L,the extract of Phalaris arundinacea under each nutrient strip promoted the growth of Microcystis aeruginosa,especially at the eutrophic level.At three nutrient levels,the extract of Phalaris arundinacea inhibited the growth of Microcystis aeruginosa,and increased with the increase of Phalaris arundinacea content.3.The growth of Microcystis aeruginosa changed by different temperature conditions.The density and specific growth rate of Microcystis aeruginosa in the experimental groups were at a low level at 15?.The growth of Microcystis aeruginosa was inhibited by the extract of Phalaris arundinacea,with the inhibition rate ranging from-9% to 75.1%.The extract of Phalaris arundinacea had an effect on the growth of Microcystis aeruginosa,which showed a phenomenon of "low promotion,high inhibition" at 25? and 30?.At 30 C,The promotion effect was more remarkable at 30 C,and the inhibition rate was-150%.Temperature had little effect on Allelopathy and algae inhibition of Phalaris arundinacea when the content of Phalaris arundinacea was more than 24g/L.4.The mechanism of allelopathic and algae-inhibiting effects of the extract of Phalaris arundinacea on Microcystis aeruginosa was analyzed mainly from the content of MDA in algae cells,extracellular polysaccharides and cell membrane permeability.When the concentration of extract was 1 g/L,the MDA content,extracellular polysaccharide content and cell membrane permeability of algae cells were less affected.With the increase of the extract concentration,the membrane lipid peroxidation of Microcystis aeruginosa increased,the permeability of algae cells increased,the activity of algae cells decreased,and the growth rate of algae cells decreased.At the same time,algae cells secrete extracellular polysaccharides to form an extracellular glue sheath to resist the effect of allelochemicals released by Phalaris arundinacea on their own growth.Under medium nutrient conditions,the density of algae cells was low;the MDA content of algae cells was high;the damage degree of cell membrane was low,and the content of extracellular polysaccharides was high.The outer sheath was formed to resist the stress of the extract of Phalaris arundinacea.The effect of allelochemicals in the extract on the growth of Microcystis aeruginosa was weakened with the increase of nitrogen and phosphorus nutrition level.The allelopathic effect of Phalaris arundinacea caused by low temperature is obvious.The density of algae cells is low,and the MDA content of algae cells is high.However,the extracellular polysaccharides are low,which makes it difficult to resist environmental stress.