The alleviative effect of exogenous phytohormones on the growth, physiology and gene expression of Tetraselmis cordiformis under high ammonia-nitrogen stress.

•High ammonia increased activities of MDA, SOD and CAT of T. cordiformis.•Inhibition to the photosynthetic activity was alleviated by phytohormones.•Phytohormones alleviated the oxidative damage of high ammonia on T. cordiformis.•The antioxidant capacity of T. cordiformis was improved by phytohormones.•Phytohormones mitigated the inhibition to glutamine synthetase-related gene.