title: TRANSFORMATION AND ALLELOPATHY OF NATURAL DISSOLVED ORGANIC CARBON AND TANNIC ACID ARE AFFECTED BY SOLAR RADIATION AND BACTERIA(1).
abstract: The aim of this study was to test whether abiotic and biotic factors may affect allelopathic properties. Therefore, we investigated how solar radiation and bacteria influence allelopathic effects of the plant-derived, polyphenolic tannic acid (TA) on microalgae. Using a block design, lake water samples with and without TA were exposed to solar radiation or kept in darkness with or without bacteria for 3 weeks. Dissolved organic carbon (DOC), specific size fractions of DOC analyzed by chromatography-organic carbon detection (LC-OCD), and concentrations of total phenolic compounds (TPC) were measured to follow the fate of TA in lake water with natural DOC exposed to photolytic and microbial degradation. DOC and TPC decreased in dark-incubated lake water with TA and bacteria indicating microbial degradation. In contrast, exposure to solar radiation of lake water with TA and bacteria did not decrease DOC. Chromatographic analyses documented an accumulation of DOC mean size fraction designated as humic substances (HS) in sunlit water samples with TA. The recalcitrance of the humic fraction indicates that photolytic degradation may contribute to a DOC less available for bacterial degradation. Subsequent growth tests with Desmodesmus armatus (Chodat) E. Hegewald showed low but reproducible difference in algal growth with lower algal growth rate cultured in photolytically and microbially degraded TA in lake water than cultured in respective dark treatments. This finding highlights the importance of photolytic processes and microbial degradation influencing allelopathic effects and may explain the high potential of allelochemicals for structuring the phytoplankton community composition in naturally illuminated surface waters.
authors.affiliation: Department of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyCentral Chemical Laboratory, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyDepartment of Limnology of Stratified Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries Alte Fischerhütte 2, 16775 Stechlin, GermanyDepartment of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Bauer
authors.affiliation: Department of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyCentral Chemical Laboratory, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyDepartment of Limnology of Stratified Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries Alte Fischerhütte 2, 16775 Stechlin, GermanyDepartment of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Zwirnmann
authors.affiliation: Department of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyCentral Chemical Laboratory, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyDepartment of Limnology of Stratified Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries Alte Fischerhütte 2, 16775 Stechlin, GermanyDepartment of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Grossart
authors.affiliation: Department of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyCentral Chemical Laboratory, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, GermanyDepartment of Limnology of Stratified Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries Alte Fischerhütte 2, 16775 Stechlin, GermanyDepartment of Shallow Lakes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Hilt
keywords: DOC; allelopathy; photodegradation; phytoplankton; polyphenols; tannic acid