The Role of Sustained Photoprotective Non-photochemical Quenching in Low Temperature and High Light Acclimation in the Bloom-Forming Arctic Diatom Thalassiosira gravida

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 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 (K E) and photosynthesis (E K), low µ max but relatively high Chl a/C, low C/N, and decreasing light-saturated carbon fixation rate (P C m) 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 photons 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.

Diversity in Xanthophyll Cycle Pigments Content and Related Nonphotochemical Quenching (NPQ) Among Microalgae: Implications for Growth Strategy and Ecology

“…, A and C; see also Lacour et al. ). Remarkably, when normalized to E/ K E , the amounts of XC pigments were very similar in both species independent of the temperature (Figs.…”

“…, Lacour et al. , ), to normalize the growth irradiance E to K E to provide a relative scaling of the energy pressure on the photosynthetic apparatus. When analyzed against E/ K E , the amount of XC pigments was better conserved among temperate and polar microalgal species (see Table ) and conditions (Figs.…”

“…Datasets documenting the effect of different growth temperatures are also scarce, and were limited to our own data (Lacour et al. ; T. Lacour, unpub. data; see Table ).…”

“…For instance, polar diatoms grown at 0°C and high irradiance show a strong retention of Dt and related sustained NPQ (Lacour et al. ).…”

Growth and Elemental Stoichiometry of the Ecologically-Relevant Arctic Diatom Chaetoceros gelidus: A Mix of Polar and Temperate

“…The maximum growth rates obtained here at LL and HL correspond to 20 and 43% of this µ max , respectively, representing a relatively small growth increment given the 36-fold difference in irradiance between the two treatments and the fact that irradiance at LL was lower than the half-saturation constant for light at 0 • C (K E = 9.5 µmol photons m −2 s −1 ; Supplementary Figure 1). Recently, it has been suggested that the relatively low growth rates at 0 • C can be attributed to the limitation of C fixation resulting from the slow catalytic activity of Rubisco (Young et al, 2015;Lacour et al, 2018). In this context, the strong control of temperature on C fixation presumably nullifies the energetic advantage of using NH + 4 .…”