MEPS - Vol. 423 - Feature article

Solar radiation induces the flux of photoreactive DOM through a heterotrophic food chain with a linkage to autotrophic plankton (mixotrophic flagellates).

Vähätalo AV, Aarnos H, Hoikkala L, Lignell R


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


In experiments by Vähätalo and co-workers, solar radiation produced labile forms of dissolved organic matter (DOM) and nitrogen, which were assimilated by bacterioplankton. The bacterioplankton was grazed by flagellates, which themselves were grazed by ciliates. Labile DOM that had been produced photochemically was thus transferred over 3 trophic levels. Photochemically produced labile forms of nitrogen also stimulated primary producers, in particular the mixotrophic flagellate Pseudopedinella. When nitrogen was the limiting nutrient for primary producers, Pseudopedinella did not assimilate the dissolved nitrogen directly, but satisfied its nitrogen demand by grazing bacterioplankton. Photochemical reactions induced by solar radiation thus link biologically recalcitrant but photoreactive DOM to microbial food webs that consist of both hetero- and autotrophs.


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