Photophysiological responses of Gracilariopsis bailinae to temperature and light intensity

There are species differences in the adaptation of macroalgae to temperature and light intensity. Gracilariopsis bailinae is a large alga that likes high temperature. In order to scientifically guide its application in mariculture and marine ecological restoration, we investigated the photosynthetic physiological responses characteristics of G. bailinae to temperature and light intensity by using chlorophyll fluorescence technology, combined with changes in photosynthetic pigment content and growth rate of algae. We measured various physiological parameters, including specific growth rate (SGR), photosynthetic pigments content Chlorophyll a (Chl a), carotenoid (Car), and phycobiliprotein, and chlorophyll fluorescence parameters Maximum photochemical efficiency of PSII (F_v/F_m), actual light conversion efficiency (Φ_PSII), electron transfer rate (ETR), photochemical quenching (qP), and non-photochemical quenching (NPQ) of G. bailinae cultured at five different temperatures (15, 20, 25, 30, 35 ℃) and four different light intensities (1 000, 3 000, 6 000, 9 000 lx). Results reveal that temperatures and light intensities had a significant interaction effect on the parameters measured, except for Car and F_v/F_m (P<0.01). The SGR, phycobiliprotein contents, and chlorophyll fluorescence parameters of G. bailinae increased significantly as temperature increased (P<0.05), whereas high light intensity treatment led to a significant decrease in photosynthetic pigments content and values of F_v/F_m, Φ_PSII, ETR, and qP, but a significant increase in NPQ and SGR (P<0.05). These results indicate that G. bailinae can enhance its survival capacity under high temperature conditions by increasing the synthesis of phycobilin, and achieve photoprotection under high light conditions by increasing heat dissipation and decreasing photosynthetic pigment synthesis.