Rhizosphere bacterial diversity and environmental function prediction of wild salt-tolerant plants in coastal silt soil

Coastal silt soil (CSS), hydraulically transported and filled by dredger and mud pump from the bottom of beach in coastal zone in the process of reclamation project, has a high salinity which poses difficulties for coastal development. The use of salt-tolerant plants to improve CSS is a green and efficient method. In this process, the rhizosphere of predominate salt-tolerant plants should enrich more functional microorganisms, which will exert an indispensable ecological influence on plant growth and benign soil transformation. Therefore, comparing the characteristics of plant rhizosphere bacterial communities with different growth capacities on the same CSS can help to find the key rhizosphere hub microorganisms, which will lay a theoretical foundation for the precise improvement of CSS. High-throughput sequencing technology was used to study rhizosphere bacterial diversity of wild salt-tolerant plants (Suaeda glauca, Tripolium vulgare, and Phragmites australis) in the CSS of Lianyun New-town, Lianyungang City, China, through α-diversity, β-diversity, community composition diversity and environmental correlation analysis, and the rhizosphere bacterial functions were predicted. The results showed that the sulfur-oxidizing bacteria (Sulfurovum, Woeseia, and Thioalkalispira) which were dominant in all samples, might impart important salt-stress resistance. Bacteroidetes and sulfate-reducing bacteria Desulfuromonas were enriched in the rhizosphere of S. glauca and P. australis. Bacteroidetes can increase the degradation of organic matter, provide electrons for sulfate-reducing bacteria, and thus promote efficient sulfur-cycling. Sulfate-reducing bacteria can serve as hub bacteria for the growth of salt-tolerant plants by connecting sulfur cycles and organic matter decomposition. In addition, S. glauca, as the dominant plant in CSS, can enrich more functional dominant bacteria, and its rhizosphere bacterial community composition was significantly positively correlated with TN and TOC. These rhizosphere bacteria include phototrophic bacteria Altererythrobacter and methane-oxidizing bacteria Methylophaga related to C cycling, Geothermobacter and Pelobacter related to Fe cycling, and nitrogen-cycle-related bacteria Marinobacterium, Halomonas, and Motiliproteus involved in nitrification/denitrification. This indicates that S. glauca growth can promote the turnover of soil C, N, S, and Fe by enriching these functional bacteria. The analysis of bacterial diversity, as an important ecological indicator, can help to understand the growth of dominant plants in CSS, and the mechanism of benign soil development. The results show that the rhizosphere of S. glauca can enrich a functionally complete bacterial community, which is beneficial to the positive evolution of CSS.