Inhibitory Effect Of Monomer Active Substances In Ginkgo Biloba Leaves On Microcystis Aeruginosa

At present,the outbreak of Microcystis aeruginosa in eutrophic water is becoming increasingly frequent,which seriously damages the ecological environment and poses a threat to human health.So,finding an efficient and environment-friendly method for controlling algae blooms has become an urgent need to maintain the stability of aquatic ecosystem.Plant-derived allelochemicals have the advantages of both chemical and biological methods in inhibiting algae.It has the characteristics of fast speed,and environment-friendly.It is one of the important breakthroughs in harmful algal blooms control.Our previous studies have shown that Ginkgo biloba extract has a significant inhibitory effect on Microcystis.In order to further explore which active substances play a major role.This paper takes Microcystis aeruginosa as the research object.We first compared and analyzed the inhibitory effects of eight active monomer substances（quercetin,catechin,kaempferol,isorhamnetin,luteolin,ginkgolide,bilobalide and ginkgolic acid）in Ginkgo biloba leaves on Microcystis aeruginosa in the laboratory.According to their inhibitory effects,we screened out typical monomer active substances and optimized their parameter settings.Then the inhibition mechanism of typical active substances was discussed from growth,photosynthetic system,respiratory system,algal cell membrane integrity and enzyme activity of Microcystis aeruginosa.Finally,by simulating the natural water environment,studied the inhibition effect of typical active substances on phytoplankton community and its influence on water body,clarified its ecological safety.The results are significant for revealing the inhibition mechanism of allelochemicals,and can provide scientific basis for new technologies for the prevention and control of Microcystis aeruginosa blooms.The main findings are as follows:（1）The order of inhibitory effects of eight active substances on the growth of Microcystis aeruginosa is quercetin,kaempferol>luteolin,ginkgolic acid>catechin,isorhamnetin>ginkgolide,bilobalide.Ginkgolide and bilobalide have no obvious inhibitory effect on Microcystis aeruginosa.Although ginkgolic acid has the strongest inhibitory effect on the photosynthetic activity of algae,due to its strong toxicity and poor ecological safety,it is not suitable for application in the natural environment.Through comparison of the effects of eight active substances on the growth,chlorophyll a content and photosynthetic activity of algae,it is believed that quercetin and kaempferol have the best comprehensive inhibition effect and are suitable for further study.（2）The concentration gradient experiments showed that the inhibitory effect of quercetin and kaempferol on Microcystis aeruginosa increased with the increase of concentration（2.5～40 mg/L）.Both quercetin and kaempferol at concentrations higher than 5 mg/L had significant inhibitory effects on Microcystis aeruginosa growth（P<0.05）.The 48 h EC₅₀ values of quercetin and kaempferol against Microcystis aeruginosa were 20.99 and 15.83 mg/L,respectively,and the 96 h EC₅₀ values were 8.76 and 11.96mg/L,respectively.At 96 h,the inhibition efficiency of 40 mg/L quercetin and kaempferol on algal density was 90.79%and 96.69%,respectively,and the chlorophyll a content and photosynthetic system of algae were significantly inhibited（P<0.01）.（3）By measuring and comparing multiple targets of action on Microcystis aeruginosa in the control and experimental group,it was confirmed that quercetin and kaempferol could affect the photosynthetic and respiratory system of algae,destroy the structure of cell membrane and the activities of superoxide dismutase（SOD）,ketose diphosphate carboxylase（Rubisco）,phosphoenolpyruvate carboxylase（PEPC）and transmembrane ATPase(Na⁺-K⁺ATPase,Ca²⁺-Mg²⁺ATPase).Comparatively speaking,kaempferol had better comprehensive algae inhibition effect than quercetin,and had no significant effect on the production and release of microcystins.（4）Through simulating natural water environment in which algal blooms broke out,we carried out a pilot scale enclosure algae inhibition experiment.The results showed that kaempferol could effectively reduce the number of cyanobacteria in water,optimize the structure of phytoplankton community,and have no significant impact on the water quality such as DO,p H,TN,TP,etc.in the enclosure.After adding kaempferol,the dominant species of phytoplankton in water quickly changed from cyanobacteria（the proportion decreased from 78.28%to 46.49%）to green algae（the proportion increased from 19.78%to 48.67%）.The community diversity was improved,with the Shannon-Weiner index rising from 1.07 to 1.83,and the Simpson index rising from 0.45 to 0.78.Through ecological safety experiments,the application of kaempferol can not only effectively inhibit harmful cyanobacteria in water,but also show no adverse impact on non-target organisms and water quality.