Ecological restoration of tidal flat and its effects on soil characteristic and bacterial community

Vegetation restoration is a vital ecological remediation technology for greening saline-alkaline soils. However, little attention is paid to the seasonal changes of soil remediation under different vegetation coverage. This study investigated a recently restored coastal tidal flat located on the island of Zhoushan, by examining shifts in physicochemical properties, enzyme activities, and bacterial communities over 1 year. Soils under Suaeda australis (SUA), Phragmites australis (PHR), Tamarix chinensis (TAM), and two hybrid treatments (SUA+PHR and SUA+TAM) were collected seasonally. Results showed that the seasonal climate variations and vegetation types played important roles in soil physicochemical properties and soil enzyme activities during vegetation restoration. Vegetation could stimulate the activities of soil microbial enzymes, of which PHR-covered soils exhibited higher catalase activities, higher alkaline phosphomonoesterase activities were observed in summer except for PHR. The combined communities had the highest urease activities in spring and summer, and the highest levels of polyphenol oxidase activity were found in summer or autumn. Furthermore, the bacterial alpha diversity revealed that SUA- and SUA+PHR-covered soils were not markedly affected as the season progressed, whereas PHR and SUA+TAM were characterized by an increase-decrease trend, as well as TAM exhibited highest in autumn. Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, and Chloroflexi were the dominant phyla in each vegetation types. This study deepens our understanding of the effects of halophyte cultivation on coastal ecosystem phytoremediation.