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Marine Ecology Progress Series

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MEPS 423:1-14 (2011)  -  DOI:

Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters

Anssi V. Vähätalo1,2,*, Hanna Aarnos1,3, Laura Hoikkala1,4, Risto Lignell1,4 

1Tvärminne Zoological Station, University of Helsinki, Hanko, Finland
2Present address: ARONIA Coastal Zone Research Team, Åbo Akademi University & Novia University of Applied Sciences, Ekenäs, Finland
3Present address: Department of Environmental Sciences, University of Helsinki, Helsinki, Finland
4Present address: Marine Center, Finnish Environmental Institute, Helsinki, Finland

ABSTRACT: We assessed the responses of a nitrogen (N)-limited <10 µm plankton community from the Baltic Sea to the 12 d photochemical transformation of dissolved organic matter (DOM). The photochemical transformation of DOM increased the biomass and the production of heterotrophic bacteria, flagellates, and ciliates in the following 10 d bioassay. The succession of heterotrophic plankton indicated a 3-level trophic transfer of photoproduced bioavailable DOM through bacteria and flagellates to ciliates. The photochemical transformation of DOM also stimulated the biomass and the production of phytoplankton through the photoproduction of bioavailable N initially incorporated into bacterial biomass. The grazing of bacterioplankton supplied N to phytoplankton directly, presumably due to mixotrophy, and indirectly by releasing dissolved N. The carbon stable isotope signature of plankton biomass was similar to that of allochthonous carbon, indicating that the photochemical transformations concerned primarily terrestrial DOM and therefore represented a microbial link between terrestrial DOM and planktonic production. The bacterial production stimulated by the photochemically produced labile DOM was related to the number of photons absorbed during the photochemical transformation of DOM for the determination of apparent quantum yield. According to the apparent quantum yield, the calculated summertime photoproduction of labile substrates contributes 2 to 5% to total bacterial production in the northern Baltic Sea. According to this study, the photochemical transformation of terrestrial DOM influences not only the initial production of bacterioplankton but can also stimulate higher trophic levels and autotrophic plankton in coastal waters.

KEY WORDS: Dissolved organic nitrogen · Apparent quantum yield · Trophic transfer · Photochemistry · Bacterioplankton · Phytoplankton

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Cite this article as: Vähätalo AV, Aarnos H, Hoikkala L, Lignell R (2011) Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters. Mar Ecol Prog Ser 423:1-14.

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