Research On Algae Inhibition Effect And Mechanism Of Plant Litter Extract

Cyanobacteria bloom phenomenon in eutrophic water have been the main environmental problem in the world.Basically,there are many severe negative effects including hypoxia,toxin production,bad odor and malodorous metabolites,which damage water quality and landscape and cause the greatest threat to aquatic ecosystem and water resources utilization.Therefore,finding a safe,high-efficiency and cheap bloom control method has been one of the most important issues in this field today.Each of traditional methods such as mixing waters using an air compressor,algicidal chemicals,biological agents using microorganisms has obvious drawbacks.In fact,some researchers believed that the allelopathy of plants maybe the effective and potential method to control the harmful blooms in eutrophic water.The plants with the bioactive substances have been considered as a potential natural algicides.Based on the conclusion of previous literature,ten types of plants reported to contain antialgal chemicals were selected from daily life in this paper.The effect of these plant litter extract on the inhibition of common harmful algae in eutrophic water was measured,and Ginkgo biloba fallen leaves extract were selected which is fast-effective,high inhibition efficiency and high ecological security.And the inhibition effect were monitored when Microcystis flos-aquae coexisted with the different concentrations G.biloba fallen leaves extract,in order to find the optimal concentration.Secondly,transcriptome analysis and RT-PCR technology were used to research the inhibitory mechanism systematically of G.biloba fallen leaves extract on M.flos-aquae from molecular level.Finally,the effect of inhibition on phytoplankton and the effect on water quality were studied by simulating the water environment under natural conditions.The specific results are as follows:?1?Study on the effect of plant litter on inhibiting algae and determination of the best plant species Ten types of plant extracts were selected for pure-culture experiments in the laboratory on three common green-blue algae,Tribonema minus,Microcystis aeruginosa and M.flos-aquae.The result showed that the inhibition effects of ten plant extracts on different algae were specificity.In general,the inhibition effect of ten plant extracts on Microcystis was better than that of T.minus.Among the four woody plants,G.biloba and Salix babylonica extract had a rapid and efficient algae inhibitory effect t on the three green-blue algae,and the inhibition effect of three herbaceous plants and three aquatic plants on Microcystis was better.?2?Exploration of the physiological and molecular mechanisms of G.biloba fallen leaves extract inhibition on M.flos-aquae With the increase of time and concentration,the inhibition effect of G.biloba fallen leaves extract on M.flos-aquae was increased gradually.The inhibition effect was stable and efficient at the 3 g L^-1,with the inhibition rate was 75.51%at 96 h.However,the inhibition effect of G.biloba fallen leaves extract with 12 g L-1 was slightly lower than that of 6 g L^-1.Transcriptome analysis and RT-PCR technology were used to verify that the photosynthesis system is an important target to inhibit M.flos-aquae by G.biloba fallen leaves extract.The different gene expression of M.flos-aquae was significant after exposed G.biloba fallen leaves extract,which include relevant genes about photosynthesis,sulfur metabolism,cell membrane and enzyme activity.The result showed that the photosynthesis activity of M.flos-aquae was significantly reduced,and the inhibition of PSII reaction center and electron transfer process was significant.?3?Effects of G.biloba fallen leaves extract on the algal growth in enclosures The effect of G.biloba fallen leaves extract on phytoplankton community structure and water quality was verified by simulating the water environment under natural conditions.The results showed that G.biloba fallen leaves extract could effectively reduce the amount of Cyanophyta and content of chlorophyll a in the water.The phytoplankton community is composed of cyanobacteria as the absolute dominant species,accounting for 92.34%of the total number of phytoplankton before the addition of G.biloba fallen leaves extract.In later stage of experiment,the dominant species of phytoplankton community in the water body changed from cyanobacteria to chlorophyta such as Coelastrum,Planktosphaeria,Micractinium and Chodatella.After 7 days,the amount of cyanobacteria decreased to 41.54%,improving the community structure of phytoplankton in water effectively.After exposing G.biloba fallen leaves extract,TN and NH₃-N reduced,and there was no significant difference with the control group.And several major physico-chemical indicators of water bodies were not significantly affected.And through ecological safety experiments,it was judged that G.biloba fallen leaves extract had no lethal effect on Brachydanio rerio and three submerged plants?Vallisneria natans,Elodea nuttallii and Myriophyllum verticillatum?.This study compared the inhibitory effects of different plants under the same conditions systematically.G.biloba fallen leaves were selected as algaecide firstly,the inhibitory mechanism and the feasibility of its application in practical engineering were analyzed in depth systematically.In addition,the effect of cyanotoxin released by Microcystis and the interaction between microorganisms and zooplankton in aquatic ecosystems are also the research topic in the future.