AQUATIC MICROBIAL ECOLOGY,2009.pdf

AQUATIC MICROBIAL ECOLOGY Aquat Microb Ecol Preprint, 2009 doi: 10.3354/ame01303 Published online June 22, 2009 INTRODUCTION Photosynthesis involves numerous pathways. In the case of oxygenic phototrophs, this involves evolution of oxygen (O2) from water (H2O) by the ‘light reactions’ and uptake of carbon dioxide (CO2) by the ‘dark reac- tions’; thus, both O2 and CO2 represent the primary ‘currencies’ by which photosynthesis operates. Tracing O2 evolution and/or CO2 uptake has long been the convention for quantifying photosynthesis rates. Thus, considerable effort has been invested in optimising tracer techniques since their introduction in the 1950s (Steeman Nielsen 1952), particularly for phytoplank- ton, which represent the most widespread and diverse group of the aquatic phototrophs and account for the majority (95%) of global aquatic productivity. Attempt- ing to reconcile productivity measurements between studies that have focused on either O2 evolution or CO2 ? Inter-Research 2009 · *Email: dsuggett@essex.ac.uk Comparing electron transport with gas exchange: parameterising exchange rates between alternative photosynthetic currencies for eukaryotic phytoplankton David J. Suggett1,*, Hugh L. MacIntyre2, Todd M. Kana3, Richard J. Geider1 1Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK 2Dauphin Island Sea Lab, 101B Bienville Blvd, Dauphin Island, Alabama 36528, USA 3Horn Point Laboratory, 2020 Horns Point Rd, Cambridge, Maryland 21613, USA ABSTRACT: Estimates of aquatic primary productivity derived from in situ active chl a fluorescence have rapidly gained popularity over the past 2 decades. This trend has been driven primarily by the need to improve upon ‘conventional’ carbon (C) uptake- or oxygen (O2) evolution-based productivity estimates that require water samples to be incubated ex situ. Unlike the conventional approaches to measuring productivity, chlorophyll fluorescence measurements inherently describe only the activity of