Application of exogenous salicylic acid on improving high temperature resistance of Nannochloropsis oceanica

The large-scale farming of Nannochloropsis spp. has long been subject to high temperature. Though salicylic acid is widely used to enhance the high temperature resistance of higher plants, related research in microalgae is still in its infancy. In this study, Nannochloropsis oceanica cells at 25 °C were transferred to high temperature (35 °C) for 96 h, during which period salicylic acid with various concentrations (0, 15, 25, 35, and 50 mg L−1) were added into high temperature groups. The results indicated that high temperature could heavily inhibit the growth of N. oceanica, and result in various physiological and biochemical changes. The addition of exogenous salicylic acid at moderate concentration distinctly alleviated the inhibition of heat stress on N. oceanica. Moreover, further analysis indicated that exogenous salicylic acid could significantly increase the contents of soluble sugars, soluble proteins, total unsaturated fatty acids, and catalase activity, but result in the decrease of the nitrate reductase activity, the malondialdehyde content, and fatty acid profile. Our results also demonstrated that salicylic acid at a concentration of 15 mg L−1 received the best growth performance of N. oceanica under 35 °C. This study investigates the thermal protection effect of salicylic acid on N. oceanica under high temperature, and can provide valuable information for the large-scale production of microalgae.