The Effect Of Reduced Phosphorus On The Growth Of Microcystis Aeruginosa

Eutrophication is the hot issue for years in which phosphorus (P) plays a vital role. Early researches mainly focused on the highest state of P (+5), little has been concerned on the existence and biogeochemical cycle of the reduced P (oxidation state less than+5) in the environment. Reduced P has been paid more attention in recent years. On one hand reduced P has been assumed to be the precursor of bio-available P source due to its high solubility in the early earth; On the other hand, its widespread use in agricultural area as fertilizer or fungicide maybe produce a lot of environmental problems.Lake Taihu is affected severely by human activities and Microcystis aeruginosa is the advantageous species in the eutrophication. In our lab group, reduced phosphite (H3PO3-,+3 valence) was detected in the pore water of the sediment from Lake Taihu, and a lot of microgranisms using phosphite as the sole P source have been screened. Study on the effect of reduced P on the growth of Microcystis aeruginosa is meaningful to explore the bioavailability of reduced of P and its relationship with eurtophication.Under the laboratory culture condition, Microcystis aeruginosa 7806 is chosen to study whether it can grow in phosphite or glyphosate medium. Results are showed as follows:1. Phosphite and glyphosate can be indirectly detected by molybdenum blue method after oxidation by potassium peroxydisulfate. Less than 5% phosphate could be detected without oxidation by potassium peroxydisulfate. The linear equation of phosphite concentration after oxidation with potassium peroxydisulfate was:y (mg P/L)= 2.17x (A700)-0.01 (R2= 0.998, n=6). Phosphite was steady in the BG-11 medium under culture conditions during 21 days. Hyphosphite was easily to be oxidized in the environment and failed to be determined by the above method.2. Phosphite of 0～54.4 mgP/L boost no cell growth, and the max cell number no more than 2×106 cells/mL when the initial cell number is 1×106 cells/mL. Compared with sole phosphate group,0～0.5 mgP/L phosphate combined with 5.44 mgP/L phosphite increase the Chlorophyll a content particularly in 0.5 mgP/L phosphate. Analysis of the maximum yield of PSII based on Chlorophyll a fluorescence indicated that Fv/Fm increased when phosphite existed in phosphate-phosphite medium. In addition, phosphite failed to support cell growth even though it more readily permeated the cells in P-deficient medium than in P-sufficient medium. Alkaline phosphatase activity (APA) analysis indicated that phosphite, unlike organic P, inhibits the response of cells to deficient P status, especially under P-deprived conditions;3. Both glyphosate and glyphosate isopropylammonium can be used as the sole P source for Microcystis aeruginosa, the cell growth depending on the different P concentrations. For glyphosate, cell number and Chlorophyll a reach the top in 5 mgP/L with 14×106 cells/mL and 0.3 mg/m3, respectively. The maximum cell numbers of 9×106 and Chlorophyll a contents of 0.2 mg/m3 were obtained with addition of 1 mgP/L glyphosate isopropylammonium, whereas 5 mgP/L of glyphosate isopropylammonium rapidly brought the cell death. APA analysis shows a normal P supply status, in accord with cell growth. Cell TP has little change under 0.1～5 mgP/L glyphosate or 0.01～0.5 mgP/L glyphosate isopropylammonium contentraion but in 0.01 mgP/L 95% glyphosate medium and free-P medium.5.44 mgP/L glyphosate equally boosts the Chlorophyll acontent and Fv/Fm when 0.5 mgP/L phosphate is supplied.