Abstract
Thalassiosira gravida is a major Arctic diatom responsible for the under-ice spring bloom. We investigated T. gravida physiological plasticity growing it at two temperatures (0°C and 5°C) and under different light intensities typically found in its natural environment. T. gravida showed remarkable thermal- and photo-acclimatory plasticity including: low light saturation parameter for growth (KE) and photosynthesis (EK), low μmax but relatively high Chl a/C, low C/N and decreasing light-saturated carbon fixation rate (PCm) with increasing growth irradiance. T. gravida also showed remarkable photoprotective features, namely a strong sustained non photochemical quenching (NPQs, hour kinetics relaxation) supported by a high amount of xanthophyll cycle pigments. T. gravida growth remained possible under a wide range of irradiances but photosynthetic plasticity was higher at moderately low light (up to ~50 µmol photon m-2 s-1), nevertheless corresponding to the mean in situ conditions under which it predominates, i.e. underneath the spring thin-ice punctuated with melting ponds. The potential role of NPQs in the photophysiological plasticity of T. gravida is discussed.
Highlights
Thalassiosira gravida is a centric diatom that is among the five most abundant phytoplankton in the Arctic Ocean (Poulin et al, 2011)
Growth Rate, C and N, chlorophyll a (Chl a) Content The growth rate of T. gravida was highly influenced by growth temperature with a maximum growth rate almost twice as high at 5◦C (0.5 d−1) than at 0◦C (0.27 d−1) (Figure 1A)
Chl a to carbon ratio (Chl a/C) in T. gravida was to some extent in the range of temperate microalgae
Summary
Thalassiosira gravida is a centric diatom that is among the five most abundant phytoplankton in the Arctic Ocean (Poulin et al, 2011) It is a major and intense spring bloomer that generally appears early during the productive season (Booth et al, 2002), when the ice-pack is still present, even blooming underneath the ice thanks to the increase in light transmittance due to the formation of melt ponds (Arrigo et al, 2012). We aimed at understanding how the major Arctic strain T. gravida thrives under the relatively large variations in irradiance and temperature in its natural habitat due to both seasonal and on-going climate change
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