The comparative study for physiological and biochemical mechanisms of Thalassiosira pseudonana and Chaetoceros calcitrans in response to different light intensities

Both Thalassiosira pseudonana and Chaetoceros calcitrans are important species of marine microalgae. Their adaptive capacity to light intensity significantly varies during actual cultivation. We investigated the responses of these two species to different light intensities at 25 °C through analyses of photoacclimation, antioxidant ability as well as many physiological and biochemical parameters. The growth rate of T. pseudonana was positively correlated with light intensity in the first 8 days. However, after that, the greatest growth rate of T. pseudonana was found at a light intensity of 40 μmol m− 2 s− 1. For C. calcitrans, the growth rate at 200 μmol m− 2 s− 1 was the highest among the three light intensities in the first 10 days, while the growth rate at 120 μmol m− 2 s− 1 became the highest after 10 days. Both algae could yield the most chlorophyll a at 40 μmol m− 2 s− 1, and β-carotene content was increased in T. pseudonana but decreased in C. calcitrans with the increase of light intensity. Moreover, maximal photochemical efficiency of PSII (Fv/Fm) and effective photochemical efficiency of PSII (Fv′/Fm′) in T. pseudonana were decreased with the increase of light intensity, while non-photochemical quenching (NPQ) and superoxide dismutase (SOD) activities were increased. However, Fv/Fm and Fv′/Fm′ in C. calcitrans under all light intensities remained relatively constant, and Fv/Fm was maintained at around 0.6. NPQ was increased and SOD activity was decreased in C. calcitrans with the increase of light intensity. These findings suggested that T. pseudonana employed a more positive physiological strategy for adaptation to environmental stress under low light intensity, while C. calcitrans possessed a good physiological strategy for adaptation to environmental stress under high light intensity. Taken together, we provided a better understanding of the growth effects of these two microalgae under different light intensities and offered novel insights into their mass culture.