Identification and nitrogen fixation effects of symbiotic Frankia isolated from <i>Casuarina</i> spp. in Zhejiang, China

Abstract

Fourteen symbiotic isolates were obtained from root nodules of Casuarina equisetifolia and Casuarina cunninghamiana in Zhejiang, China. All isolates exhibited typical Frankia morphological characteristics, including filamentous hyphae, vesicles, and multilocular sporangia borne terminally or in an intercalary position. Combined with 16S rDNA sequence alignment results, all isolates were identified as Frankia spp. 4 isolates belonged to the physical Group A, 7 to Group B, and 3 to Group AB. The strains demonstrated varied nitrogenase activities, with the ZCN192 strain being the highest (2.897 μmol·mg^-1h^-1) and ZCN199 the lowest (0.056 μmol·mg^-1h^-1). After in vivo inoculation, all strains significantly increased seedling height, basal diameter, and dry biomass of Casuarina spp. Generally, strains with higher nitrogenase activities exhibited more effective nitrogen fixation in vivo.

Keywords: Casuarina spp., Frankia, identification, nitrogen fixation effect.