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Aquatic Microbial Ecology

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AME 56:123-131 (2009)  -  DOI:

Net and gross productivity: weighing in with 14C

John Marra*

Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA

ABSTRACT: Data from the 14C method, C assimilation time courses and single endpoint comparisons to O2 fluxes, imply 2 different things. Time course (linear) experiments suggest that C assimilation measures gross production while the single endpoint comparisons with O2 fluxes suggest that the 14C method approximates net community production. Considering only phytoplankton metabolism, a way out of the paradox is to assume that all CO2 respired by mitochondria is refixed in photosynthesis, meaning that photosynthesis uses more H2O than CO2 from the ambient environment since the latter has an internal source. The 14C method, therefore, would estimate net primary production relative to O2 fluxes in the absence of heterotrophic interactions. The method can also be applied to the estimation of phytoplankton respiration from the nighttime loss of labeled organic matter. A summary of available data shows that C assimilation corrected for organic C lost is statistically equivalent to gross production measured independently using the 18O method.

KEY WORDS: Productivity · Phytoplankton · Photosynthesis · 14C · Refixation

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Cite this article as: Marra J (2009) Net and gross productivity: weighing in with 14C. Aquat Microb Ecol 56:123-131.

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