The Mechanism Of Low Dissolved Phosphorus And Allelopathic Inhibition On Growth Of Microcystis Aeruginosa

The Microcystis aeruginosa(M.aeruginosa)blooms and Spartina alterniflora(S.alterniflora)invasion have caused serious damage to local ecological environment,which has attracted wide attention of scholars at home and abroad.Phosphorus is an indispensable nutrient element for algae growth.M.aeruginosa blooms are very easy to occur under high phosphorus conditions.The study found that M.aeruginosa blooms also occur under low phosphorus conditions,so revealing the occurrence mechanism is very important for preventing and controlling blooms,but the mechanism is not completely clear.The plants of S.alterniflora have allelopathy,which can effectively inhibit the growth of other species through allelopathy.However,there is little research about its allelopathy on harmful algae.On the basis of revealing the occurrence mechanism of M.aeruginosa blooms under lowphosphorus conditions,utilizing the allelopathy of S.alterniflora to control the growth of M.aeruginosa can provide a new idea for simultaneously controlling M.aeruginosa blooms and S.alterniflora invasion.Therefore,the growth parameters of M.aeruginosa,total phosphorus(TP)concentration,activity of alkaline phosphatase(AP)and catalase(CAT),and expression of phosphate transporter gene in culture medium were determined to clarify the mechanism of phosphorus uptake by M.aeruginosa under low phosphorus limitation and the effect of dissolved organic phosphorus(DOP)on the proliferation of M.aeruginosa.Combined with the algal density,extracellular organic matter(EOM)structure,chlorophyll a(Chl-a)content and recognition of effective components in allelochemicals to reveal the inhibitory effect and mechanism of S.alterniflora extract on M.aeruginosa growth,and its impact on the aquatic microenvironment was analyzed from a safety perspective.The main research conclusions are as follows:Under low phosphorus limitation,M.aeruginosa can hydrolyze DOP to dissolved inorganic phosphorus(DIP)by AP to obtain the available phosphorus required for growth.The phosphate transporter gene expression of M.aeruginosa was significantly up-regulated,which was inversely correlated with the phosphorus concentration.The CAT activity will only increase significantly if it is limited to a certain level by low phosphorus.The higher the degree of low phosphorus limitation,the higher the CAT activity.Therefore,M.aeruginosa may respond to phosphorus demand in low-phosphorus environments and respond to environmental phosphorus changes by enhancing the transport of DIP,strengthening its antioxidant capacity,and shifting to DOP,which may be an important reason why M.aeruginosa can grow rapidly and even form water blooms in the low phosphorus environment.The inhibitory effect on M.aeruginosa growth became more stronger with the increasing S.alterniflora extract concentration by decreasing Chl-a and weakening photosynthesis when the concentration was over 0.05 g/mL.The results of GC-MS showed that Cyclohexane,Heptane,2-Cyclohexen-1-one,Hexadecanoic acid,2,4-Di-tertbutylphenol and Hydrocinnamic acid may be the main allelochemicals.In addition,the results of high-throughput sequencing show that S.alterniflora extract had little effect on the structure and diversity of microbial communities in the culture system.In conclusion,this study elucidates the formation mechanism of M.aeruginosa blooms in low phosphorus water,and verifies the feasibility of using the allelopathy of S.alterniflora to control M.aeruginosa blooms,which provides an effective way to solve the problem of M.aeruginosa blooms and S.alterniflora invasion simultaneously.