Abstract: In order to understand interspecific competition of live prey microalgae, the effect of nitrogen-phosphorus ratio (N/P) on the interspecific competition of Chlorella pyrenoidosa and Isochrysis zhanjiangensis was investigated by adding NaNO₃ and KH₂PO₃ as N and P sources. Under monoculture mode, C. pyrenoidosa normally grew with N/P ranging from 4 to 22 and was inhibited when the ratio was over 22, while I. zhanjiangensis was not obviously affected. Co-culture mode could promote the growth of C. pyrenoidosa and inhibit the growth of I. zhanjiangensis. C. pyrenoidosa owned an obviously competitive advantage in the co-culture mode, especially when N/P was 13 and 16. C. pyrenoidosa could be co-cultured with I. zhanjiangensis in large scale production, which might increase the output of C. pyrenoidosa and provide the possibility to harvest mixed microalgae as live food for aquaculture.

Key words: 1-aminocyclopropane-1-carboxylate deaminase, plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, microbiome, Piriformospora indica