Fig 1.
Specimens of the five diatom species viewed with scanning electron microscopy.
Scale bars represent 1 μm. Credits Nantes Culture Collection (NCC). Navicula phyllepta and Entomoneis paludosa are epipelic; Biremis lucens and Planothidium delicatulum are epipsammic; Plagiogrammopsis vanheurckii is tychoplanktonic.
Fig 2.
DES versus light intensity after 5 min exposure for the three growth forms.
●Epipelic (Navicula phyllepta and Entomoneis paludosa); ■Epipsammic (Biremis lucens and Planothidium delicatulum); ◆Tychoplanktonic (Plagiogrammopsis vanheurckii). Averaged DES were fitted using the model proposed by [37], vertical bars represent standard deviation.
Table 1.
Pigment ratios relative to chlorophyll a of each strain, expressed in g.g-1 Chl a.
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.
Fig 3.
Relationships between NPQ and DES (a) and LUE and DES (b) for the three growth forms. ●Epipelic (Navicula phyllepta and Entomoneis paludosa); ■Epipsammic (Biremis lucens and Planothidium delicatulum); ◆Tychoplanktonic (Plagiogrammopsis vanheurckii). Equations of non-linear regressions are reported in the text (Eqs 8 and 9). Dashed lines represent 95% CI.
Fig 4.
Typical radiometric spectra from B. lucens cultures exposed to three different light intensities.
(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 a, Chl c and again Chl a (see text and [29]). The box delimits the absorption domain due to DD and DT xanthophylls (Fig 5).
Fig 5.
Zoom from Fig B for standardized second derivative over the absorption domain due to xanthophyll pigments involved in the XC (DD and DT) between 480 and 530 nm.
Shoulders are assigned to absorption features of DD and DT from literature (DD1: [30]; DT3: [17]; and DT4NPQ: [31,38] and from this study (DD+DT2LL, DD+DT2 and DD+DT2HL). For details see text.
Table 2.
Spectral indices calculated using second derivative value standardized to the Chl c red absorption band (δδ632) and explaining more than 40% of the variability (R2 > 0.4) of the LUE estimated by PAM-fluorometry using Navicula phyllepta (N. phyl) and Biremis lucens (B. luce) data set.
The lowest values of RSME (= Root Mean Square Error), in bold, to predict LUE for Entomoneis paludosa (E. palu) Planothidium delicatulum (P. deli) and Plagiogrammopsis vanheurckii (P. vanh) are those selected (Eqs 8 to 13). ***: linear regression p ≤ 0.001; n.t.: not tested.
Table 3.
Spectral indices calculated using second derivative from DD-DT xanthophyll pigments absorption band (see Fig 5) and explaining more than 40% of the variability (R2 > 0.4) of the LUE estimated by PAM-fluorometry using Navicula phyllepta (N. phyl) and Biremis lucens (B. luce) data set.
The lowest values of RSME (= Root Mean Square Error), in bold, to predict LUE for Entomoneis paludosa (E. palu) Planothidium delicatulum (P. deli) and Plagiogrammopsis vanheurckii (P. vanh) are those selected (Eqs 8 to 13). ***: linear regression p ≤ 0.001; n.t.: not tested.
Fig 6.
Optical absorption cross-section a*.
Retrieved from the MPBOM transfer radiative model [27] and averaged over the Chl a absorption domain (670 to 685 nm) and for all species. Vertical bars represent standard deviation.
Fig 7.
Measured ETR (from PAM fluorometry) vs. predicted ETR (from radiometric measurements using the MPBLUE index).
The dash line is the slope (= 0.93) of the linear regression (R2 = 0.92, p<0.001). All species and growth forms were included: ●Epipelic (Navicula phyllepta and Entomoneis paludosa); ■Epipsammic (Biremis lucens and Planothidium delicatulum); ◆Tychoplanktonic (Plagiogrammopsis vanheurckii).
Fig 8.
Spectra from B. lucens culture, after 5 min in the dark at different spectral resolutions.
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 a, Chl c and again Chl a were still observable. Reflectance is presented in arbitrary unit (A.U) to avoid overlaying of spectra.
Table 4.
Spectral resolution (full width at half maximum, FWHM) and corresponding sensors used to simulate new spectra and retrieve new a* and MPBLUE values for estimating ETR.
Slope and R2 of linear regression between ETR estimated from fluorometry and radiometry are reported. All regressions are significant (p < 0.001), except (1); (2) Future sensors; (3) Spectral sampling is indicated when different of the FWHM.