Release Of Extracellular Amino Acids From Three Species Of Algae And Its Contribution To Dissolved Organic Nitrogen

In recent years,algal bloom broke out frequently caused by nutrients enriched and degree of eutrophication increased constantly in lakes with industrial and agricultural production and biological activity.Amino acids and dissolved organic nitrogen(DON)were an important part of the biogeochemical cycles and life process,were important bio-availability of nutrients in water,were also important for algal extracellular organic matter(EOM)reproduction and distribution.An important endogenous for amino acids and DON of algal extracellular organic matter(EOM)in water,studied on amino acid and DON content and composition have great significance to clear the mechanism of occurrence for lake eutrophication.In this study,through compares the type and composition of DON and amino acids in algal growth period,discusses amino acid releasing and its contribution to organic nitrogen between different algae.The typical freshwater algae species such as Microcystis aeruginosa,Scenedesmus quadricauda and Navicula rhynchocephala were selected as cultivation objects,and typical algae-type lake such as Dianchi lake to explore the characteristic difference of the content and composition of extracellular free amino acid(DFAA)and combined amino acids(DCAA)in the growth phase of algaes and algal boom break out and extincted period,by Excitation-emission matrix spectroscopy combined with parallel factor analysis(EEMs-PARAFAC)and precolumn high performance liquid chromatography(HPLC).And discussed the contribution of algae-source amino acids on DON.In growth period of algae,organic matter were abounding released,inorganic nitrogen changed into DON and released into water,DON becomes the main nitrogen forms.In algae growth exponential phase and stable phase,algae massive absorbed TDN,algal growth has an absorbent role of nitrogen in the lake water,in algal decay process,algae released increased nitrogen.4 species of component were obtained such as tryptophan-like(C1)humic-like(C2),protein-like(C3)and tyrosine-like(C4),through EEM-PARAFAC analysised on EOM.The content of tryptophan-like,humiclike and tyrosine-like are constantly increased.The content of DFAA and DCAA were constantly cumulative trend in algae growth period,and it abounding released in early decline period.The content of DON,DFAA,DCAA and amino acids Microcystis aeruginosa were the highest amount of contribution,respectively.Therefore cyanobacteria bloom may release lots of amino acids to increase organic nitrogen load in freshwater ecosystem.The algae released large amounts of nitrogen nutrients into the water,in algal eruptive period and extinction period in Dianchi Lake The concentration TDN,NH4+ and DON increased by 2.65 mg/l,1.21 mg/l,and 0.82 mg/l respectively.And organic matter also had a large number of releases in algal extinction period.4 fluorescent components were obtained such as tryptophan-like(C1’),terrestrial humic-like(C2’),tyrosine-like(C3’),terrestrial humic-like(C4’)by EEM-PARAFAC.Tryptophan-like and tyrosine-like had the same identify result with cultural research.The released content were significantly increased of C1’ and C3’ in algal extinction period.In algal extinction period,the concentration of DFAA and DCAA increased 7.99 μmol/L and 19.9 μmol/L respectively.Algal metabolism is the main source of amino acids in algaetype lake.The concentration of glycine,arginine and alanine concentrations were higher,it had a similar results of the indoor culture experiments.The contribution to DON of DFAA,DCAA,THAA were 14.2~43.6%,4.7~26.2%,and 14.7~69.5% in water.Therefore,the important source of organic nitrogen in Lake was algal growth and algal decline,its produced algal-source organic nitrogen and amino acids are important source of DON,provided nutrition for algal outbreak in lake.Therefore,it was difficult to achieve better results of only shut off the external source of organic nitrogen input to solve lake-eutrophication problems.