Study Of Synergistic Effect Of Iron And Phosphorus On Growth Of Three Typical Freshwater Algae And Allelopathic Competition Mechanism

As the eutrophication of lake is serious,algal bloom appeared more frequently in China.The outbreak of algal bloom destroy the ecological structure of the original lake(reservoir)environment,affect the development of fisheries and aquatic resources;cause malodorous black river,damage the urban landscape and city image;and the secretion of algal toxins seriously endanger human health.It has practical significance to study the mechanism of algal bloom and to study seeking the method of algal bloom prevention and control.Iron is an indispensable element in the process of algae growth.It can participate in photosynthesis,respiration,coordination of reactive oxygen species,protein and nucleic acid synthesis,enzymatic reaction and other growth and metabolism process.Phosphorus is an essential nutrient for the growth of algae.Phosphorus plays a key role in the eutrophication of water body and is the first limiting factor in the growth of algae in natural freshwater lakes.The effect of iron and phosphorus on algal growth is not irrelevant,but synergetic.The allelopathic effect is that a plant or a microorganism releases some chemicals into the environment during its growth and forms a microenvironment area around it that promotes or inhibits the growth of other plants or microorganis ms in the region.Algae also have such phenomena,and allelopathic is a key factor of algae community change.In this study,the effects of iron and phosphorus on the growth and synergy of three typical freshwater algae(Anabeana flos-aguae,Scenedesmus quadricauda and Melosira sp.)were studied experimentally.As well as the competitive growth of three algae and studing the allelopathic competition mechanism of Scenedesmus quadricauda for Anabeana flos-aguae.The results showed that the biomass of Anabeana flos-aguae,Scenedesmus quadricauda and Melosira sp.were " inhibited after promoting it " with the increase of iron concentration under different initial iron concentration.Three kinds of algae have their own optimal growth threshold of iron concentration,which is less than the threshold to make the algae appear iron limit,affecting its growth.When the iron concentration is higher than this threshold,the iron element is excessively absorbed and the absorption of the phosphorus element is affected.The three kinds of algae reached the optimum growth conditions under the initial concentration of 0.6 mg/L.At different initial phosphorus concentrations,when the initial phosphorus concentration is less than 0.25 mg/L,the growth rate of Anabeana flos-aguae will be limited.When the initial phosphorus concentration is less than 0.125 mg/L,the growth rate of Scenedesmus quadricauda will be limited.Under the experimental conditions,the threshold of Anabeana flos-aguae was 0.5-1 mg/L,and the threshold of Scenedesmus quadricauda was 0.25-1 mg/L.It is considered that the explosive growth of algae requires the concentration of iron and phosphorus to reach the optimal growth threshold at the same time.The concentration of iron and phosphorus in the environment has an interactive effect on the absorption of algae.When there is excessive iron in the environment,it will promote the absorption of more phosphorus and iron elements by the three kinds of algae.In the competitive growth of Anabeana flos-aguae,Scenedesmus quadricauda and Melosira sp.,Scenedesmus quadricauda are dominant algae species.Experiments show that Scenedesmus quadricauda can make Anabeana flos-aguae perish,and Scenedesmus quadricauda on Melosira sp.inhibition.The concentration of phosphorus in the environment will affect the allelopathy of Scenedesmus quadricauda to Anabeana flosaguae.The experimental results show that Scenedesmus quadricauda must have enough phosphorus to secrete enough allelopathy to affect Anabeana flos-aguae.Different types of complex iron will affect the allelopathy of Scenedesmus quadricauda to Anabeana flosaguae,the experiment shows that EDTA-Fe is the most favorable iron form for this allelopathic phenomena,iron oxalate is the most unfavorable.Experiments show that the advantage of Scenedesmus quadricauda to Anabeana flos-aguae is due to the allelopathy of Scenedesmus quadricauda.The allelopathic substances secreted by Scenedesmus quadricauda are specific and selective and need to be released in contact wi th Anabeana flos-aguae,which causes the substance to fail.It is speculated that the allelochemical is a class of protein.Through the MWD and EEM detection,algae in the pure culture conditions will secrete less of the various substances into the environ ment,and mixed culture will greatly increase the secretion of various substances.Experimental results show that one of the key factors in the competitiveness of algae is reflected in its control of the surrounding microenvironment,and this "control" mos tly requires algae to secrete various metabolites.Once a certain kind of algae occupies the environment,it considers the environment to be relatively "safe" and algae will choose to reduce the release.And that the original release of these products will slowly break down failure.