AB 3:121-131 (2008)  -  DOI: https://doi.org/10.3354/ab00069

Evaluation of imaging and conventional PAM as a measure of photosynthesis in thin- and thick-leaved marine macroalgae

Hanne Dalsgaard Nielsen1,*, Søren Laurentius Nielsen2

1School of Life Sciences, Napier University, 10 Colinton Road, Edinburgh EH10 5DT, UK
2Department of Environmental, Social and Spatial Change, Roskilde University, PO Box 260, 4000 Roskilde, Denmark

ABSTRACT: The present paper compares light-response patterns of electron transport rate (ETR) measured by imaging and conventional pulse-amplitude-modulated fluorescence (PAM) with that of gross O2 evolution in naturally thin-leaved (Ulva lactuca) and thick-leaved (Fucus serratus) algae, as well as in 1 to 8 cell layer thick ‘artificial thalli’ built from layers of Enteromorpha intestinalis. At sub-saturating and saturating irradiances imaging ETR/ETRmax provided a very accurate reflection of P/Pmax, which was different in thin and thick algae. There was no effect of tissue thickness on conventional ETR/ETRmax, which was unrelated to P/Pmax at low irradiances. At super-saturating irradiances, imaging ETR/ETRmax was reduced significantly compared to P/Pmax, which instead corresponded to conventional ETR/ETRmax. Imaging Fm was only related to thallus thicknesses from 1 to 4 cell layers but not beyond. Photoinhibition expressed by imaging PAM in thick thallus may have been compensated for by photosynthesis in deeper cells. Conventional Fm was linearly related to thallus thickness from 1 to 8 cell layers. No photoinhibition was indicated at super-saturating irradiances by conventional PAM and O2 evolution measurements that integrate the photosynthetic performance of the entire thallus of thick algae. At irradiances <80 µmol m–2 s–1, the O2/conventional ETR ratio was close to 0.25, whereas it decreased at higher irradiances in both thin and thick macroalgae. The O2/imaging ETR ratio was >0.25 and increased further at super-saturating irradiances, in particular in thin algae. In conclusion, the type of PAM instrument may influence the light response of ETR. Likewise, the thallus thickness may affect the relationship between O2 evolution and ETR. ETR recordings should be treated with caution and regarded as a compliment to O2 measurements, particularly when thick-leaved macroalgae are studied.

KEY WORDS: Chlorophyll fluorescence · Electron transport · Brown algae · Light saturation · O2/ETR ratio · Photosynthesis · Photoinhibition · PAM

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Cite this article as: Nielsen HD, Nielsen SL (2008) Evaluation of imaging and conventional PAM as a measure of photosynthesis in thin- and thick-leaved marine macroalgae. Aquat Biol 3:121-131. https://doi.org/10.3354/ab00069

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