Effects Of Fe³⁺ On The Growths Of Three Common Algae In Fresh Water

Fe is one of the essential elements for the growth of organisms, and was thought to be the most important elements in the growth of algae except N and P. In this paper, three common algae in freshwater (Microcystis aeruginosa; Oscillatoria tenuis; Scenedesmus quadricauda) were selected and incubated in the lab under different Fe³⁺ concentrations in culture media, viz. 0, 10, 100, 1000, 10000, 30000 nmol/L, to investigate the effects of Fe³⁺ on the growths and the nutriment uptake of three algae. The growth and physiological index including biomass, concentration of chlorophyll a were determined. Furthermore, the effects of Fe³⁺ on the superficial structure of Microcystis aeruginosa and Scenedesmus quadricauda were observed through scan electron microscope. The results showed as follows:(1) The growth of Microcystis aeruginosa was restrained under low Fe³⁺ concentrations ( 0 to 100 nmol/L). When the Fe³⁺ concentration reached to 30000 nmol/L , the growth of Microcystis aeruginosa was accelerated in the first 20 days of incubation, and then a fast decrease of the biomass and the concentration of chlorophyll a were observed. The photos of SEM implied that it may be due to the death or autolyzing of the algae cells. The uptake of N and P by Microcystis aeruginosa increased with Fe³⁺ concentration in culture media. However, the uptake of Ca2+ and Mg2+ in 10000 nmol/L Fe³⁺ were higher than that in 30000 nmol/L Fe³⁺.(2) The growth of Oscillatoria tenuis was restrained under low Fe³⁺ concentrations. The biomass and the concentration of chlorophyll a were enhanced with the rising of Fe³⁺ concentration. The specific growth rate in exponential period of growth reached to the top when Fe³⁺ concentration was at 10000nmol/L. The uptake of N and P by Oscillatoria tenuis increased with the growing of Fe³⁺ concentration. However, the uptake of Ca2+ and Mg2+ in 10000 nmol/L Fe³⁺ were higher than that in 30000 nmol/L Fe³⁺, it was the same as the case in Microcystis aeruginosa.(3) The growth of Scenedesmus quadricauda was restrained under Fe³⁺ concentrations between 0 to 10nmol/L. When the Fe³⁺ concentrations were higher than 10000nmol/L, the growth of Scenedesmus quadricauda were increased slowly with the rising of the Fe³⁺ concentration. The growth was not restrained when the Fe³⁺ concentration was at 30000 nmol/L .The uptake of nutrient elements (N, P, Ca and Mg) were all augmented as the rising of Fe³⁺ concentration. The influence of Fe³⁺ concentration on superficial structure of Scenedesmus quadricauda was not evident, which indicated that Scenedesmus quadricauda was more tolerant to the metal.