Effects Of IAA On The Physiological Characteristics Of Microcystis Aeruginosa And Cylindrospermopsis Raciborskii And The Competition Between The Two Algae

In this study,the effects of IAA on the physiological and biochemical characteristics of Microcysti aeruginosa and Cylindrospermopsis raciborskii,and the competition between the two algae were investigated.The main results are as follows:(1)Low concentration of IAA showed inhibitory effect on the growth of M.aeruginosa.Chl a and carotenoid content in the short term exposure under IAA were increased,and then these promoting effects slowed down.Cell viability was significantly decreased by IAA on the 2ed day,and then the inhibitory effect was slowed down.High concentration of IAA can inhibit the growth of M.aeruginosa and reduce the protein content in algal cells.The contents of phycocyanin and allophycocyanin in Microcystis were decreased under high concentration of IAA.During the experimental stage,the synthesis of polysaccharides was inhibited by IAA.Low concentration of IAA inhibited the secretion of extracellular polysaccharide from Microcystis,but this inhibitory effects was weakened with the increase of IAA concentration,and the secretion of extracellular polysaccharide was even promoted by IAAat high concentration.IAA had no significant effect on the activity of alkaline phosphatase in the M.aeruginosa.Low concentration of IAA in the short term of exposure increased the peroxide algal cell plasma membrane,whereas,high concentrations of IAA decreased the oxidative damage of cytoplasmic membrane.(2)The growth of C.raciborskii was was promoted by IAA at low concentration but inhibited at high concentration.IAA slightly inhibited the synthesis Chl a.The carotenoid content was promoted by IAA on the 4th day of the experiment,but it was inhibited on the 6th day.IAA increased the cell viability C.raciborskii at low concentration,but decreased its cell viability at high concentration.In the short term of exposure,IAA promoted the intracellular protein synthesis of C.raciborskii.Low concentration of IAA can promoted the synthesis of phycocyanin and allophycocyanin.The content of extracellular polysaccharide in C.raciborskii increased with the increase of IAA concentration on the 6th day.The low concentration of IAA could promote the intracellular polysaccharide content of C.raciborskii,but the high concentration of IAA could inhibit it.High concentration of IAA inhibited the uptake of phosphorus by C.raciborskii,but enhanced the extracellular alkaline phosphatase activity of algal cells.In the early stage of IAA esposure,the cytoplasmic membrane of C.raciborskii was damaged by oxidative damage,but the action time was very short.The high concentration of IAA decreased the oxidative damage of the cytoplasmic membrane within 4 days.However,the oxidative damage of cytoplasmic membrane enhanced on the 6th day.(3)C.raciborskii and M.aeruginosa co-culture results showed that the number of cells in the 2nd day M.aeruginosa was higher than that of C.raciborskii when the IAA was not added under the appropriate conditions of nutrition and light,and the number of algal cells was poor at the 4th day Values were decreased,but M.aeruginosa was still higher than C.raciborskii,and the number of cells at the 6th day was equal,indicating that C.raciborskii's cell growth was faster than M.aeruginosa.After adding IAA,the number of cells at C.raciborskii was higher than that of M.aeruginosa at 4th day.C.raciborskii is clearly more competitive.Especially in the low concentration of IAA conditions,C.raciborskii cell number is much higher than M.aeruginosa.