Effect of Light Intensity and Light Quality on Diatom Behavioral and Physiological Photoprotection

Abstract

In this study, we investigated the different photoregulation responses of diatom dominated natural biofilms to different light intensities and wavelengths, over a tidal cycle in the laboratory. We compared the overall effect of light spectral quality from its light absorption (Qphar) dependent effect. Two different conditions were compared to study photoprotective strategies: sediment (migrational) and without sediment (non-migrational). Three different colors (blue, green, and red) and two light intensities (low light, LL at 210 µmol.photons.m −2 .s −1 and high light, HL at 800 µmol.photons.m −2 .s −1) showed strong interactions in inducing behavioral and physiological photoprotection. Non-migrational biofilm non-photochemical quenching (NPQ) was much more reactive to blue HL than red HL while it did not differ in LL. We observed a biphasic NPQ response with a light threshold between 200 and 250 µmol.photons.m −2 .s −1 of Qphar that elicited the onset of physiological photoprotection. Similar HL differences were not observed in migrational biofilms due to active vertical migration movements that compensated light saturating effects. Our results showed that within migrational biofilms there was an interaction between light quality and light intensity on cell accumulation pattern at the sediment surface. This interaction led to inverse diatom accumulation patterns between blue and red light at the same intensity: LL (blue + 200.67%, red + 123.96%), HL (blue + 109.15%, red + 150.34%). These differences were largely related to the differential amount of light absorbed at different wavelengths and highlighted the importance of using wavelength standardized intensities. Different vertical migration patterns significantly affected the total pigment content measured at the surface, suggesting that cell could migrate downward more than 2 mm as a photoregulatory response. Colloidal carbohydrates patterns paralleled the vertical migration movements, highlighting their possible role in diatom motility. Our data strongly suggests a wavelength and Qphar dependent light stress threshold that triggers upward and downward movements to position microphytobenthic diatoms at their optimal depth.

Light intensity and spectral composition drive reproductive success in the marine benthic diatom Seminavis robusta

“…The dependency of mating on blue light (and to a lower extent green light) in S. robusta and C. didymus 50 is in line with a general propensity of blue light to regulate various cellular processes in diatoms, such as cell cycle progression, phototaxis, vertical migration and production of metabolic compounds such as the pigment marennine 32 , 33 , 36 , 37 , 58 , 76 . The identification of functional red-light phytochromes in diatoms 19 and species-specific red light responses in motility and sinking 37 , 38 , 77 has recently challenged this perspective, suggesting that red light sensing plays a more important role in diatoms than was previously anticipated.…”

“…Cells generally move upwards towards the sediment surface under moderate light intensities and migrate deeper into the sediment in darkness and under very high light intensities, resulting in synchronized rhythmic migration patterns over diurnal cycles 32 – 35 . Illumination experiments covering different wavelength ranges have shown that phototaxis and surface accumulation of motile diatoms is in most cases dependent on the presence of blue light 32 , 33 , 36 , 37 . Stauroneis phoenicenteron , on the other hand, is attracted to low intensity red light, suggesting that different benthic species employ different types of photoreceptors 24 , 38 .…”

Mapping the Intertidal Microphytobenthos Gross Primary Production Part I: Coupling Multispectral Remote Sensing and Physical Modeling

“…Such a migration scheme in the GPP algorithm was set according to the observation of the progressive superficial sediment covering by MPB during emersion at our study site (Herlory et al, 2004). However, the migration speed can be faster [a few minutes; see Méléder et al (2003b)] or slower [one hour; see Paterson et al (1998)], and it is mainly controlled by the tidal cycle and the light climate and spectral quality (Pinckney and Zingmark, 1991;Spilmont et al, 2007;Coelho et al, 2011;Barnett et al, 2020;Prins et al, 2020), but also by temperature (Cohn et al, 2003), nutrient availability in the sub-surface of sediment (Kingston, 2002), and desiccation (Coelho et al, 2009). Currently, the GPP-algorithm does not include the short-term variations of MPB photosynthetically active biomass at the sediment surface (i.e., "micro-migrations"), as it has been also observed some days/timings during our field campaigns.…”

A glance at the French-speaking diatomist community (ADLaF 2019 meeting)

“…Among abiotic stressors mentioned during the meeting (pesticides, nanoparticles, natural radioactivity…), the expected increase in frequency and intensity of extreme events due to climate change is a concern shared by both freshwater and marine diatomists: parallel works are ongoing to evaluate the effects of heat waves on benthic diatoms of intertidal mudflats and intermittent rivers (Béchet et al 2017). Finally, several contributions have shown that microphytobenthos research is still very active with several ongoing European research projects studying the factors driving biodiversity and the functioning of these benthic microbial communities (Koekodder et al 2019;Prins et al 2020), or the biodiversity and valorisation of the 'blue diatoms' (Poulin et al 2019) and their marennine-like pigments (e.g. Gastineau et al 2018).…”