Nutrient availability as major driver of phytoplankton-derived dissolved organic matter transformation in coastal environment
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Incubation experiments were performed to examine the processing of fresh autochthonous dissolved organic matter (DOM) produced by coastal plankton communities in spring and autumn. The major driver of observed DOM dynamics was the seasonally variable inorganic nutrient status and characteristics of the initial bulk DOM, whereas the characteristics of the phytoplankton community seemed to have a minor role. Net accumulation of dissolved organic carbon (DOC) during the 18-days experiments was 3.4 and 9.2 µmol l−1 d−1 in P-limited spring and N-limited autumn, respectively. Bacterial bioassays revealed that the phytoplankton-derived DOC had surprisingly low proportions of biologically labile DOC, 12.6% (spring) and 17.5% (autumn). The optical characteristics of the DOM changed throughout the experiments, demonstrating continuous heterotrophic processing of the DOM pool. However, these temporal changes in optical characteristics of the DOM pool were not the same between seasons, indicating seasonally variable environmental drivers. Nitrogen and phosphorus availability is likely the main driver of these seasonal differences, affecting both phytoplankton extracellular release of DOM and its heterotrophic degradation by bacteria. These findings underline the complexity of the DOM production and consumption by the natural planktonic community, and show the importance of the prevailing environmental conditions regulating the DOM pathways.
KeywordsExtracellular release Autochthonous organic matter Carbon cycling Colored dissolved organic matter
This study was supported by the BONUS COCOA project (Grant Agreement 2112932-1), funded jointly by the EU and Danish Research Council. The authors would like to thank Colin Stedmon (DTU Aqua, Denmark) for the DOC analysis. L.H. was supported by a grant from the Brazilian program Science without Borders/CAPES (Grant No. 13581-13-9). P.M. was supported by a postdoctoral fellowship from The Natural Sciences and Engineering Research Council of Canada (NSERC).
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