Divergence of photosynthetic strategies amongst marine diatoms

Abstract

Marine phytoplankton, and in particular diatoms, are responsible for almost half of all primary production on Earth. Diatom species thrive from polar to tropical waters and across light environments that are highly complex to relatively benign, and so have evolved highly divergent strategies for regulating light capture and utilization. It is increasingly well established that diatoms have achieved such successful ecosystem dominance by regulating excitation energy available for generating photosynthetic energy via highly flexible light harvesting strategies. However, how different light harvesting strategies and downstream pathways for oxygen production and consumption interact to balance excitation pressure remains unknown. We therefore examined the responses of three diatom taxa adapted to inherently different light climates (estuarine Thalassioisira weissflogii, coastal Thalassiosira pseudonana and oceanic Thalassiosira oceanica) during transient shifts from a moderate to high growth irradiance (85 to 1200 μmol photons m-2 s-1). Transient high light exposure caused T. weissflogii to rapidly downregulate PSII with substantial nonphotochemical quenching, protecting PSII from inactivation or damage, and obviating the need for induction of O2 consuming (light-dependent respiration, LDR) pathways. In contrast, T. oceanica retained high excitation pressure on PSII, but with little change in RCII photochemical turnover, thereby requiring moderate repair activity and greater reliance on LDR. T. pseudonana exhibited an intermediate response compared to the other two diatom species, exhibiting some downregulation and inactivation of PSII, but high repair of PSII and induction of reversible PSII nonphotochemical quenching, with some LDR. Together, these data demonstrate a range of strategies for balancing light harvesting and utilization across diatom species, which reflect their adaptation to sustain photosynthesis under environments with inherently different light regimes.

Influence of Light Conditions on Microalgae Growth and Content of Lipids, Carotenoids, and Fatty Acid Composition

“…From the ecological and physiological points of view, the different composition of microalgae pigments demonstrates differences in the ability of algae to use light of different spectral composition for photosynthesis and to develop niches with different lighting conditions [18,27,30,70]. Therefore, when cultivating microalgae, the spectral composition of light is an important growth parameter [71,72].…”

“…Carotenoids play an important role in the photosynthesis processes of microalgae, as additional pigments, as well as in the mechanisms of photoprotection when exposed to high intensity light. Photoprotective mechanisms involving carotenoids in algae are quite diverse and have been discussed in detail in a number of recent works [67,70,115,116].…”

Shade lichens are characterized by rapid relaxation of non-photochemical quenching on transition to darkness

“…Environments characterized by particularly large light fluctuations include shallow waters. Here, microalgae employ rapidly reversible NPQ, presumably to cope with more variable light fields, whereas motile benthic algae display sustained NPQ (Fisher et al 2020). For example, Derks & Bruce (2018) compared the induction and relaxation of NPQ in two diatoms from contrasting habitats.…”

Optical determinations of photophysiology along an ecological gradient in the North Pacific Ocean

“…and coccolithophores (Emiliania huxleyi) in the northern transition zone waters. These taxonomic classes tend to be low-light adapted, with E k values of 84 AE 11 and 115 μmol photons m À2 s À1 respectively and reach higher productivity at light saturation (Edwards et al 2016), although strong adaptations have been noted for species in the genus Thalassiosira (Fisher et al 2020).…”