Abstract: A total of 14 symbiotic bacterial strains were isolated from the root nodules of Casuarina equisetifolia and C. cunninghamiana in Zhejiang Province. All the strains exhibited typical Frankia morphological characteristics, including filamentous hyphae, vesicles, and multilocular sporangia borne terminally or in intercalary position. The 16S rDNA sequencing showed that all the strains were of Frankia, 4 of them belonging to physical group A, 7 belonging to physical group B, and the other 3 belonging to physical group AB. All the strains presented nitrogenase activity, but the activity differed significantly with the strains. Strain ZCN192 had the highest nitrogenase activity (2.897 μmol·mg^-1·h^-1), while ZCN199 had the lowest one (0.056 μmol·mg^-1·h^-1). After in vivo inoculated with all the strains, the plant height, basal diameter, and dry biomass of C. equisetifolia and C. cunninghamiana increased significantly, and overall, the strains with higher nitrogenase activity exhibited more obvious nitrogen fixation effect in vivo.

Key words: UV-B, Competition, Ozone depletion, Wheat