DIFFERENTIAL RESPONSE TO LIGHT INTENSITY IN 14C-BICARBONATE VERSUS 3H-LEUCINE INCORPORATION BY PROCHLOROCOCCUS AT STATION ALOHA.
There is a growing appreciation for the ability of Prochlorococcus to assimilate organic compounds, in particular amino acids, and that this uptake is enhanced by light. However, it is yet not fully understood whether the enhancement by light is directly coupled to Prochlorococcus primary productivity (autotrophic growth) or is by an independent light energy mediated mechanism. Here we present experiments conducted at Station ALOHA in the North Pacific Subtropical Gyre (NPSG) of 14C-bicarbonate assimilation (primary production/autotrophy) and 3H-leucine incorporation (mixotrophy/photoheterotrophy) by Prochlorococcus. Multi-depth, in situ incubations throughout the euphotic zone (5-175 m) as well as photosynthetron experiments on selected samples were performed to elucidate rate responses. In photosynthetron experiments, deep chlorophyll maximum populations showed a more light sensitive response for leucine uptake than 14C-bicarbonate. Depth resolved primary productivity (14C-PP) and 3H-leucine uptake showed that the PP:Leu ratios were highest in the upper water column and that this ratio declined with depth. These results indicate that light enhanced leucine incorporation may not be directly coupled to autotrophic growth in Prochlorococcus.
Björkman, K. M., University of Hawaii, USA, firstname.lastname@example.org
Doggett, J. K., University of Hawaii, USA, email@example.com
Church, M. J., University of Hawaii, firstname.lastname@example.org
Karl, D. K., University of Hawaii, USA, email@example.com
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