Screening of Casuarina equisetifolia rhizosphere-promoting bacteria and their effects on seed germination and seedling growth.

To promote the growth of Casuarina equisetifolia and address the abnormalities in the structure and function of rhizosphere soil microbial community, we isolated eight strains with multiple functions from the root nodules of C. equisetifolia, including nitrogen fixation (N), production of cell wall-degrading enzymes (protease and cellulase), auxin (IAA) production, siderophore production, ammonia (NH3) production, and phosphate solubilization. Among these strains, LB08, LB18, LB19, LB42, LB46, LB63, and LB69 were identified as Paenibacillus species, while LQ10 was identified as a Brucella sp. Results of seed soaking experiments showed that all the eight strains promoted the growth of C. equisetifolia seedlings. Strain LB69 significantly increased the germination rate and seedling vigor by 19.7% and 28.3%, respectively. Strain LQ10 significantly enhanced root length and root vigor by 48.2% and 334.4%, respectively. Strains LB18 and LB42 had the strongest effects on early shoot length and biomass accumulation, with increases of 22.4% and 32.8%, respectively. After seed soaking, the number of isozymes bands of polyphenol oxidase, superoxide dismutase, and peroxidase increased, with some bands showing enhanced intensity and increased diversity of enzyme isoforms, thereby enhancing stress resistance. In summary, the addition of these eight strains promoted plant growth and antioxidant enzyme activity, indicating their potential role as biofertilizers.