Fluorescence and absorption characteristics of dissolved organic matter excreted by phytoplankton species of western Bay of Bengal under axenic laboratory condition

• Published in: Journal of experimental marine biology and ecology Vol. 445; pp. 148 - 155
• Main Authors: Chari, N.V.H.K., Keerthi, Suman, Sarma, Nittala S., Pandi, Sudarsana Rao, Chiranjeevulu, Gundala, Kiran, Rayaprolu, Koduru, Umadevi
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.07.2013; Elsevier
• Subjects: a350/a440; Agronomy. Soil science and plant productions; Algal cultures; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Closterium; Cylindrotheca closterium; Dissolved organic matter; Fluorescence to absorption coefficient ratio; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Odontella aurita; Parallel factor analysis; Plant aquaculture, algal production (macroalgae); Sea water ecosystems; Synecology; Tetraselmis; Indian Ocean; Bay of Bengal; ISW, Bangladesh, Bengal Bay; a350/a440; Algal cultures; Dissolved organic matter; Parallel factor analysis; Fluorescence to absorption coefficient ratio; Laboratory study; a; Factor analysis; Fluorescence; Absorption coefficient; Laboratory; Marine environment; Absorption; Phytoplankton; Ratio; Algal culture
• ISSN: 0022-0981; 1879-1697
• DOI: 10.1016/j.jembe.2013.03.015

Phytoplankton exudates are major source of dissolved organic matter (DOM) in the Sea. We examined the absorption and fluorescence characteristics of Tetraselmis spp, Cylindrotheca closterium and Odontella aurita exudates in an axenic culture experiment. The objective was to test the ability of phytoplankton to produce fluorescent DOM (FDOM) apart from protein fluorescent matter in the absence of bacteria, and if so how does the fluorescence efficiency expressed as fluorescence-absorption coefficient ratio of different FDOM components compare. Through our study, the ratio of absorption coefficients at 350nm and 440nm (a350:a440 ratio) has the potential to be a unique descriptor of the growth condition of algae. It was minimum (4.12±0.59, n=14) in the growth phase for the three species. The spectral slope (S300–440) indicates that higher molecular weight compounds are present in exudates when phytoplankton grows than during lag or decay. Protein (tryptophan) like fluorescence was contained in exudates throughout the life cycle. It constituted the most abundant component also, ca., ~69% of total fluorescence in Tetraselmis spp, and C. closterium, and ~62% in the larger celled O. aurita. The remaining fluorescence was made up of humic like fluorophores of the UV (two varieties), Visible and Marine types, all of which showed maxima at the end of exponential stage. The accumulated fluorescence at the close of the experiment surviving photochemical degradation was maximum for the visible humic fluorophore in Tetraselmis sp. (~187%) and for the protein like fluorophore in O. aurita (71%). •Phytoplankton cultured axenically excrete coloured and fluorescent DOM.•The FDOM is of three humic types besides the major protein type.•The a350:a440 ratio was lowest and uniform during growth.•Fluorescence efficiency of visible humic fluorophore agrees with reported values.•Results have implication in the biogeochemical cycling of trace metals.