Abstract:Eelgrass () beds, one of the most important coastal ecosystems, are highly ecologically and economically valuable. However, eelgrass beds have been reduced worldwide because of natural and anthropogenic causes. To restore the degraded eelgrass beds, numerous studies have been conducted and various techniques developed. Among them, eelgrass transplantation is the most widely used and intensively studied technology. Some studies have shown that appropriate artificial propagation methods can effectively promote the survival and growth of the transplants, and phosphate-solubilizing microorganisms not only provide phosphate for the growth of the plants, the metabolites also play a major role in promoting plant growth and controlling diseases. However, techniques for promoting the growth of transplanted eelgrass are still absent. Therefore, investigating phosphate-solubilizing bacteria within the eelgrass rhizosphere is necessary. In this study, the growth-promoting activities of the rhizobacteria of eelgrass were investigated, by isolating four phosphate-solubilizing bacteria (P1, P2, P3, and P4) from the rhizosphere sediments of eelgrass using an SRSM medium. Based on the morphological, physiological, and biochemical characteristics, and the sequence analysis of 16S rDNA, we identified P1 as Escherichia coli, and P4 as . The optimal culture conditions and typical growth curves for the four rhizobium strains were established. The optimal temperatures for the growth of the four strains were 34.67℃, 33.95℃, 34.60℃, and 31.19℃, respectively. The optimal salinity for growth was 27.10, 28.29, 29.54, and 26.08, respectively. The optimal pH for growth was 8.26, 7.92, 8.17, and 8.21, respectively. A pot test was conducted to investigate the effects of the four phosphate-solubilizing bacteria strains on eelgrass growth. The results showed that the survival rate, growth, physiological status, and enzyme activity of the rhizosphere soil in the four inoculation treatments increased to some extent. Among the treatments P2 showed the best promoting effect, with the new leaf area, aboveground productivity, and belowground productivity being (54.31±4.79) cm2, (3.58±0.36) mg/(shoot·d), and (0.28±0.04) mg/(shoot·d), respectively. Additionally, the contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids significantly increased in the P2 treatment with values of 31.35 μg/cm2, 12.57 μg/cm2, 39.42 μg/cm2, and 6.21 μg/cm2, respectively. Except for P4, the activity of alkaline phosphatase in all other inoculation treatments was significantly increased (<0.05). However, no significant differences were observed in the soil urease activity between the inoculation and control treatments. A comprehensive analysis indicated that (the P2 strain) could be applied in the future development and application of microbial inoculants and seagrass phosphobacterial fertilizers, thereby benefitting the recovery of eelgrass beds in the future.
