Growth form defines physiological photoprotective capacity in intertidal benthic diatoms

Abstract

In intertidal marine sediments, characterized by rapidly fluctuating and often extreme light conditions, primary production is frequently dominated by diatoms. We performed a comparative analysis of photophysiological traits in 15 marine benthic diatom species belonging to the four major morphological growth forms (epipelon (EPL), motile epipsammon (EPM-M) and non-motile epipsammon (EPM-NM) and tychoplankton (TYCHO)) found in these sediments. Our analyses revealed a clear relationship between growth form and photoprotective capacity, and identified fast regulatory physiological photoprotective traits (that is, non-photochemical quenching (NPQ) and the xanthophyll cycle (XC)) as key traits defining the functional light response of these diatoms. EPM-NM and motile EPL showed the highest and lowest NPQ, respectively, with EPM-M showing intermediate values. Like EPL, TYCHO had low NPQ, irrespective of whether they were grown in benthic or planktonic conditions, reflecting an adaptation to a low light environment. Our results thus provide the first experimental evidence for the existence of a trade-off between behavioural (motility) and physiological photoprotective mechanisms (NPQ and the XC) in the four major intertidal benthic diatoms growth forms using unialgal cultures. Remarkably, although motility is restricted to the raphid pennate diatom clade, raphid pennate species, which have adopted a non-motile epipsammic or a tychoplanktonic life style, display the physiological photoprotective response typical of these growth forms. This observation underscores the importance of growth form and not phylogenetic relatedness as the prime determinant shaping the physiological photoprotective capacity of benthic diatoms.

Microphytobenthos Primary Production Estimated by Hyperspectral Reflectance

“…the MPBLUE index (δδ496/508) because it was independent of species and growth forms. This is an unexpected result because diatom growth forms strongly affect eco-physiological response to light exposure as demonstrated previously by [17]. It was confirmed by the present work with expected differences between epipsammon and epipelon deepoxydation responses (i.e.…”

“…The only pigment ratio that changed with light intensities was the xanthophyll cycle DES ratio estimating the conversion of the DD into DT with increasing light intensity ( Figure 2). As expected (see [17]), the epipelic growth form showed the lowest DES values (reaching 17.37% ± 2.26 SD) together with thycoplankton (reaching 20.72 % ± 0.76 SD).…”

“…Growth-forms are known to strongly affect eco-physiological response to light exposure: Non Photochemical Quenching (NPQ) and xanthophyll cycle (XC) patterns [17,18]. Epipelic (moving freely between sediment particle) and epipsammic species (living in close association with individual sand grain) show respectively low and high NPQ values and XC efficiency during high light exposure, whereas thycoplanktonic species show a light response similar to epipelon [17].…”

“…Five diatoms species were selected from a previous study [17] to carry out spectroradiometric and PAM-fluorescence measurements. These species were isolated from natural MPB biofilms and are kept in the Nantes Culture Collection (NCC WDCM 856) (Figure 1).…”

“…After each PAM and radiometry measurement, 1mL was filtered (Isopore TM quantification [30] is detailed in [17]. All pigments were normalized to Chl a content (g.g…”