Optical absorption cross-section a*.

<p>Retrieved from the MPBOM transfer radiative model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197093#pone.0197093.ref027" target="_blank">27</a>] and averaged over the Chl <i>a</i> absorption domain (670 to 685 nm) and for all species. Vertical bars represent standard deviation.</p

Spectra from <i>B</i>. <i>lucens</i> culture, after 5 min in the dark at different spectral resolutions.

<p>From the top (dark line) to the bottom (clear grey line): 1 nm (original data from ASD), 3.26 nm (HySpex simulation), 3.5 nm (CASI simulation), 6 nm (EnMap simulation), 10 nm (AVIRIS, Hyperion and HypXim simulation) and 15 nm (DAIS and HyMap simulation). Specific absorption features around 496, 540, 588, 632 and 673 nm respectively due to DD+DT, Fuco, Chl <i>a</i>, Chl <i>c</i> and again Chl <i>a</i> were still observable. Reflectance is presented in arbitrary unit (A.U) to avoid overlaying of spectra.</p

Typical radiometric spectra from <i>B</i>. <i>lucens</i> cultures exposed to three different light intensities.

<p>(5 min): 0 (black line), 665 (grey line) and 1950 (clear grey line) μmol photons.m^-2.s^-1. a/ Standardized reflectance; b/ Standardized second derivative. Arrows show absorption bands at 496, 540, 588, 632 and 673 nm respectively due to DD+DT, Fuco, Chl <i>a</i>, Chl <i>c</i> and again Chl <i>a</i> (see text and [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197093#pone.0197093.ref029" target="_blank">29</a>]). The box delimits the absorption domain due to DD and DT xanthophylls (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197093#pone.0197093.g005" target="_blank">Fig 5</a>).</p

Spectral indices calculated using second derivative value standardized to the Chl c red absorption band (<i>δδ</i>₆₃₂) and explaining more than 40% of the variability (R² > 0.4) of the LUE estimated by PAM-fluorometry using <i>Navicula phyllepta</i> (<i>N</i>. <i>phyl</i>) and <i>Biremis lucens</i> (<i>B</i>. <i>luce</i>) data set.

<p>The lowest values of RSME (= Root Mean Square Error), in bold, to predict LUE for <i>Entomoneis paludosa</i> (<i>E</i>. <i>palu</i>) <i>Planothidium delicatulum</i> (<i>P</i>. <i>deli</i>) and <i>Plagiogrammopsis vanheurckii</i> (<i>P</i>. <i>vanh</i>) are those selected (Eqs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197093#pone.0197093.e008" target="_blank">8</a> to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197093#pone.0197093.e013" target="_blank">13</a>). ***: linear regression p ≤ 0.001; n.t.: not tested.</p

Photosynthetic and physiological properties, and photosynthetic pigment content of <i>Pseudo-nitzschia multistriata</i>.

<p>The measurement of photosynthetic and physiological properties was performed on cells in the exponential growth phase, during preacclimation, the day before the experiments started. The growth rate did not change during experiments. _relETR_max, maximal relative electron transport rate (in mol e⁻ g Chl <i>a</i>⁻¹ h⁻¹); Ek, saturation light for photosynthesis (in µmol photons m⁻² s⁻¹); µ, growth rate (in d⁻¹); F_v/F_m, photosystem II maximal photochemical efficiency. Values are means ± SD (<i>n</i> = 9). Chlorophyll <i>a</i> cellular content (Chl <i>a</i>, in 10⁻¹⁶ mol Chl <i>a</i> cell⁻¹) and photosynthetic accessory pigments Chl <i>a</i>⁻¹ content (in mol pigment/100 mol Chl <i>a</i>) measurements were performed during experiments. Fuco, fucoxanthin: Chl <i>c</i>, chlorophyll <i>c</i>₁,₂,₃. Pigment data are means ± SD of the all data set (<i>n</i> = 135).</p

Influence of the kinetics of light increase on the photoprotection modulation.

<p>(A) Evolution of the number of absorbed photons per Chl <i>a</i> integrated over time (integrated absorbed light, Int Abs Light; expressed in mol photons mg Chl <i>a</i>⁻¹) over the light gradient, at the PFD peaks of 100, 250, 350, 500 and 650 µmol photons m⁻² s⁻¹, during the 5 h (white dots), 3 h (black squares) and 2 h kinetics of light increase (black triangles). Induction of the sustained light-acclimated NPQ (NPQ_sl; B) and evolution of the de-epoxidation state (DES = Dt/[Dd+Dt]; C) <i>versus</i> Int Abs Light during the 5 h (white dots), 3 h (black squares) and 2 h kinetics of light increase (black triangles). Values are means ± SD (<i>n</i> = 3).</p

Preacclimation and experimental light conditions.

<p>(A) <i>Pseudo-nitzschia multistriata</i> cells were grown under a sinusoidal light regime set to peak at the PFD of 100 µmol photons m⁻² s⁻¹ (preacclimation light, PL; dashed line). After two weeks of preacclimation, cells in the exponential growth phase were shifted to three experimental light treatments, the 5 h (diel cycle-related PFD increase; B), 3 h and 2 h kinetics of light increase (mixing-related PFD increases; C and D, respectively), each characterized by light gradual increases peaking at the PFD of 100, 250, 350, 500 and 650 µmol photons m⁻² s⁻¹. In each panel, experimental light increases (solid lines) are compared to PL (dashed line). Triplicate samples were taken at three sampling time points during light increase (dots, B−D). Firstly, cultures were sampled in darkness. Then, after 3 h (5 h kinetics), 2 h (3 h kinetics), and 1.5 h (2 h kinetics), samples were taken at the PFD of 42, 123, 150, 164 and 280 µmol photons m⁻² s⁻¹ for the light condition peaking at 100, 250, 350, 500 and 650 µmol photons m⁻² s⁻¹, respectively. Lastly, cultures were sampled at PFD peaks.</p

Pigment ratios relative to chlorophyll <i>a</i> of each strain, expressed in g.g^-1 Chl <i>a</i>.

<p>Values are the mean of ratios obtained at the end of each light exposure (from 0 to 1950 μmol photon.m^-2.s^-1) ± variation coefficient. Growth form is presented for each strain.</p

Non-photochemical fluorescence quenching (NPQ), and relationship between NPQ formation and diatoxanthin (Dt) synthesis.

<p>Induction of NPQ over the light gradient in <i>Pseudo-nitzschia multistriata</i> cells experiencing light gradual increases peaking at the PFD of 100, 250, 350, 500 and 650 µmol photons m⁻² s⁻¹, during the 5 h (A), 3 h (C) and 2 h kinetics of light increase (E). Values are means ± SD (<i>n</i> = 3). Relationship (<i>n</i> = 45) between NPQ and Dt Chl <i>a</i>⁻¹ (in mol Dt/100 mol Chl <i>a</i>) in <i>P. multistriata</i> cells during the 5 h (B), 3 h (D) and 2 h kinetics of light increase (F). Black and white dots are data measured at PFD ≤280 and ≥350 µmol photons m⁻² s⁻¹, respectively.</p

Xanthophyll cycle modulation.

<p>Evolution of diatoxanthin (Dt)/chlorophyll (Chl) <i>a</i> (in mol Dt/100 mol Chl <i>a</i>) over the light gradient, in <i>Pseudo-nitzschia multistriata</i> cells experiencing light gradual increases peaking at the PFD of 100, 250, 350, 500 and 650 µmol photons m⁻² s⁻¹, during the 5 h (A), 3 h (C) and 2 h kinetics of light increase (E). Values are means ± SD (<i>n</i> = 3). Relationship between Dt and diadinoxanthin (Dd)/Chl <i>a</i> (in mol pigment/100 mol Chl <i>a</i>), during the 5 h (B), 3 h (D) and 2 h kinetics of light increase (F). In (B) and (F) data measured at PFD ≤350 µmol photons m⁻² s⁻¹ (black dots, <i>n</i> = 39) and ≥500 µmol photons m⁻² s⁻¹ (white dots, <i>n</i> = 6) are discerned. In (D) data measured at PFD ≤250 µmol photons m⁻² s⁻¹ (black dots, <i>n</i> = 33), at 280 and 350 µmol photons m⁻² s⁻¹ (grey dots, <i>n</i> = 6), and at PFD ≥500 µmol photons m⁻² s⁻¹ (white dots, <i>n</i> = 6) are discerned.</p