Photo-regulation in microphytobenthos from intertidal mudflats and non-tidal coastal shallows

Abstract

International audienceThe study investigated seasonal changes in the photo-regulatory mechanisms of microphytobenthosfound in intertidal mudflats (Aiguillon Bay, the Atlantic, France) and non-tidal sandy coastal shallows(Puck Bay, the Baltic, Poland) based on photosynthetic pigment characteristics and the estimates ofphotosynthetic parameters obtained through oxygen evolution measurements. The intertidal communitiesconsisted of motile diatom species typical of epipelon. The non-tidal microphytobenthos wascomposed of epipsammic species mostly belonging to four taxonomic groups chiefly contributing to theassemblage biomass, namely cyanobacteria, euglenophytes, green algae and diatoms (comprising mainlysmall-sized species). The epipelon was low light acclimated as shown by the lower values of photoprotective/photosynthetic (PPC/PSC) carotenoids and diatoxanthin/diadinoxanthin (Dt/Dd) ratios. Incontrast, the epipsammon exhibited features of high light acclimation (high PPC/PSC and Dt/Dd ratios). Inboth microphytobenthos types, the photosynthetic capacity (Pm) showed the same seasonal variationpattern and there were no statistically significant differences between the investigated sites in correspondingseasons (P > 0.05). In both assemblage types, the photosynthetic efficiency at limiting irradiance(a) decreased over time. The epipelon had higher a compared to the epipsammon. Seasonal changesof the photoacclimation index (Ek) estimated for the epipelic communities reflected variations observedin Pm, whereas in the epipsammon an increasing trend in Ek values was observed. Ek was always higherfor the epipsammon when comparing analogous seasons, which further corroborated low and high lightacclimation in the epipelic and epipsammic communities, respectively. The presence of the photoinhibitionparameter (b) in the epipelon and the lack of it in the epipsammon suggested that the latterwas resistant to high irradiance and the physiological mechanisms were sufficient to protect it fromphotoinhibition. In the epipelon, a downturn in photosynthetic rates showed that it was susceptible tohigh light intensities, suggesting that physiological photoprotective mechanisms must be supported bybehavioural photoacclimation in order to avoid damaging light influence

Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non‐motile intertidal benthic diatom

“…In contrast, an epipelic species, Seminavis robusta, shows a less dynamic NPQ, despite concerted de novo synthesis of both Dtx molecules and LHCX proteins. Our findings add to the physiological underpinning of the differential response of motile and non-motile diatom species Juneau et al 2015) and of benthic diatom communities in sediment Pniewski et al 2015;Cartaxana et al 2016b) to their environment.…”

“…While our knowledge of NPQ regulation is mostly based on studies of planktonic diatoms, whose light climate is mostly governed by water column turbulence, far less attention has been paid to NPQ regulation in benthic diatoms thriving in, and on, the sediments of intertidal flats (Jesus et al 2009;Perkins et al 2010;Cartaxana et al 2011Cartaxana et al , 2016aSerôdio et al 2012;Lavaud and Goss 2014;Ezequiel et al 2015;Laviale et al 2015;Pniewski et al 2015). Like terrestrial plants, these diatoms can experience fast light fluctuations, not buffered by a water column, during low tide.…”

Ecophysiological characteristics of red, green, and brown strains of the Baltic picocyanobacterium <i>Synechococcus</i> sp. – a laboratory study

“…The curves were plotted on the basis of laboratory results (Clark oxygen electrode measurements) using the equation of Jassby and Platt (1976). According to a photoacclimation model description (Prezelin, 1981;Prezelin and Sweeney, 1979;Ramus, 1981;Richardson et al, 1983;Pniewski et al, 2015), the results of the present study indicated changes in photosynthetic unit (PSU) sizes as the photoacclimation mechanism, which occurred most frequently (Table 1). There were also P − E curves pointing to some changes in enzymatic reactions and the altering of accessory pigments' activity.…”

On biotic and abiotic drivers of the microphytobenthos seasonal cycle in a temperate intertidal mudflat: a modelling study

“…The MPB biofilm faces strong daily and seasonal variations of mud surface temperature (MST) caused by heating through solar irradiance during low tide exposure periods (Harrison and Phizacklea, 1985;Harrison, 1985;Guarini et al, 1997) and develops phenological adaptations. Blanchard and Cariou-Le Gall (1994), Barranguet et al (1998) and Pniewski et al (2015) 20 showed a light-related seasonal adjustment of photosynthetic parameters (the photosynthetic capacity P b max and the light saturation parameter E k ) from Production-Irradiance (P-E) curves fitted on the model of Platt and Jassby (1976). Photoinhibition was rarely observed in the field since epipelic diatoms can achieve "micro-migrations", i.e.…”

“…The light saturation parameter corresponds to the irradiance at which photosynthesis switches from light reactions (light absorption and photochemical energy conversion) to dark reactions (reductant utilization) (Sakshaug et al, 1997). It has been reported to vary seasonally in benthic microalgae (Blanchard and Cariou-Le Gall, 1994;Barranguet et al, 1998;Light and Beardall, 2001;Pniewski et al, 2015;. Cells increase their light saturation parameter at 10 high irradiance (summer) and reduce it with decreasing light levels (Sakshaug et al, 1997).…”