engleski

Antarctic phytoplankton communities’ composition determines the carbon metabolism of free-living prokariotes while sinking to the ocean interior

The Ross Sea is one of the most productive areas in the Southern Ocean, and is characterized by a pronounced export of particulate organic carbon to the mesopelagic (up to 50% of surface primary production). This organic carbon downward flux is deeply regulated by its interactions with prokaryotic communities within the entire water column. During austral summer 2017, we performed four microcosm experiments by providing freshly produced algal detritus to free-living prokaryotic communities (<1 µm) collected from the surface and from the mesopelagic zone (500 to 1000m) The aim of the study was to characterize the effect of the detritus on the uptake of dissolved inorganic and organic carbon (bicarbonate and leucine), on the growth rates and on the organic matter degradation patterns performed by deep-sea prokaryotes. The algal detritus derived from phytoplankton net samples considerably differed among the four stations, both qualitatively and quantitatively (dominance of Phaeocystis antarctica vs. several diatom genera). After a 2-day acclimation stage, mesopelagic prokaryotes took advantage of the organic carbon surplus by increasing their growth rates, more pronouncedly than the surface communities. The great difference in the quality of the detritus was reflected in different responses in prokaryotic metabolism overall. Our data indicate that the uptake of bicarbonate (likely mediated by chemosynthetic processes) can be highly enhanced by detrital material, having profound implications for the role of mesopelagic prokaryotes as a secondary sink of atmospheric CO2 after the demise and downward export of phytoplanktonic blooms.

Prokaryotes ; Ross Sea ; Phytodetritus ; C production

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