Gross and net primary production: closing the gap between concepts and measurements

Abstract

We are living at a time when accurate knowledge of the magnitude of the drawdown of inorganic carbon by autotrophic metabolism is especially crucial to our understanding of global carbon cycling and the functioning of the global ecosystem. Since algae contribute approximately half of the planet's annual primary productivity, understanding the processes contributing to the net assimilation of CO 2 is critical. In this paper, we briefly discuss the range of approaches to measurements of aquatic photosynthesis that have been used, including more recent developments such as fluorescence and stable isotope studies, and whether these provide data that reflect net or gross productivity. We then consider the range of processes that run counter to photosynthetic carbon assimilation, with emphasis on respiration (and its measurement) and excretion of dissolved organic carbon, and how these affect our estimates of net primary production. We conclude by briefly assessing how future changes in global climate might impact not just overall primary productivity, but also the balance between net and gross carbon assimilation.KEY WORDS: Primary productivity · Photosynthesis · Respiration · Algae · Protein turnover · Homeostasis · Fluorescence Resale or republication not permitted without written consent of the publisherContribution to AME Special 2 'Progress and perspectives in aquatic primary productivity'

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