MEPS 376:85-101 (2009)  -  DOI:

Effect of water column light gradient on phytoplankton fluorescence transients

M. Raateoja1,4,*, B. G. Mitchell2, H. Wang2, E. Olivo3

1Finnish Institute of Marine Research, 00560 Helsinki, Finland
2Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0218, USA
3Université Pierre et Marie Curie, 75005 Paris, France
4Present address: SYKE Marine Centre, 00251 Helsinki, Finland

ABSTRACT: The light management of phytoplankton can be assessed in situ on time scales shorter than those of the non-photochemical fluorescence quenching (qn) mechanisms. We adopted fast repetition rate fluorometry to water column studies in the northwest Pacific Ocean and its adjacent shelf seas. Near-surface depression of the photochemical energy conversion efficiency (PECE) (effective Fq’/Fm’ and maximum Fv’/Fm’; Fq’ = Fm’ – F’, Fv’ = Fm’ – Fo’; Fq’ and Fv’ are variable fluorescence yields in the light, Fv’ is that with maximum photochemical quenching; fluorescence yields in the light: Fm’ maximum, F’ steady-state, and Fo’ minimum) defined specific zones according to whether PECE was depressed by photochemistry (relaxation of photochemical quenching, qp) or photoprotection/photoinhibition (increase of qn). qp seemed to be the main factor depressing PECE, and the depressing effect of qp on PECE also extended to considerably deeper depths than that of qn. When moving towards the surface, the qn effect overrode the qp effect on the PECE decrease at depths of 8 to 13 m, depending on the station. The vertical trends of Fq’/Fm’ and Fv’/Fm’ were modelled according to a typical P–E (photosynthesis–irradiance) dependence to supplement the 14C-based P–E data. E(Fq’/Fm’) and E(Fv’/Fm’) were the light levels at which the vertical trends of Fq’/Fm’ and Fv’/Fm’, respectively, started to decrease. Although the nutrient regime is the main controller of primary photochemistry in general, the ambient light also becomes the controlling factor on PECE whenever the light level rises above E(Fq’/Fm’). At E(Fv’/Fm’), light ultimately overrides the effect of the nutrient status on PECE. E(Fv’/Fm’) also marks the light level at which the photoprotective measures first become necessary. This level is close to the onset of the plateau phase producing the 14C-based light-saturated photosynthetic rate Pmax.

KEY WORDS: Pacific Ocean · Phytoplankton · FRR · Fluorescence · Quenching · Photochemical

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Cite this article as: Raateoja M, Mitchell BG, Wang H, Olivo E (2009) Effect of water column light gradient on phytoplankton fluorescence transients. Mar Ecol Prog Ser 376:85-101.

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