Predicting the Electron Requirement for Carbon Fixation in Seas and Oceans

Publication Type:
Journal Article
PLoS ONE, 2013, 8 (3)
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Marine phytoplankton account for about 50% of all global net primary productivity (NPP). Active fluorometry, mainly Fast Repetition Rate fluorometry (FRRf), has been advocated as means of providing high resolution estimates of NPP. However, not measuring CO 2 -fixation directly, FRRf instead provides photosynthetic quantum efficiency estimates from which electron transfer rates (ETR) and ultimately CO 2 -fixation rates can be derived. Consequently, conversions of ETRs to CO 2 -fixation requires knowledge of the electron requirement for carbon fixation (Φ e,C , ETR/CO 2 uptake rate) and its dependence on environmental gradients. Such knowledge is critical for large scale implementation of active fluorescence to better characterise CO 2 -uptake. Here we examine the variability of experimentally determined Φ e,C values in relation to key environmental variables with the aim of developing new working algorithms for the calculation of Φ e,C from environmental variables. Coincident FRRf and 14 C-uptake and environmental data from 14 studies covering 12 marine regions were analysed via a meta-analytical, non-parametric, multivariate approach. Combining all studies, Φ e,C varied between 1.15 and 54.2 mol e - (mol C) -1 with a mean of 10.9±6.91 mol e - mol C) -1 . Although variability of Φ e,C was related to environmental gradients at global scales, region-specific analyses provided far improved predictive capability. However, use of regional Φ e,C algorithms requires objective means of defining regions of interest, which remains challenging. Considering individual studies and specific small-scale regions, temperature, nutrient and light availability were correlated with Φ e,C albeit to varying degrees and depending on the study/region and the composition of the extant phytoplankton community. At the level of large biogeographic regions and distinct water masses, Φ e,C was related to nutrient availability, chlorophyll, as well as temperature and/or salinity in most regions, while light availability was also important in Baltic Sea and shelf waters. The novel Φ e,C algorithms provide a major step forward for widespread fluorometry-based NPP estimates and highlight the need for further studying the natural variability of Φ e,C to verify and develop algorithms with improved accuracy. © 2013 Lawrenz et al.
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