Seasonal variations in soil physicochemical properties and microbial community structure influenced by Spartina alterniflora invasion and Kandelia obovata restoration

Spartina alterniflora invasion has initiated one of the greatest changes to occur in coastal wetlands in China, and ecological replacement using mangrove species such as Kandelia obovata is an effective method for controlling these invasions. The effects of S. alterniflora invasions and subsequent K. obovata restorations on soil microbial community structures in different seasons are still not fully understood. In this study, soil samples were collected from six vegetation types (unvegetated mudflat, invasive S. alterniflora stands, one-/eight-/ten-year K. obovata restoration areas, and native mature K. obovata forests) in summer and winter. The variations in the soil microbial community structure between the vegetation types across two seasons were then characterized based on 16S rRNA gene sequencing, and the physicochemical properties that shaped the microbial communities were also determined. The invasion and restoration processes significantly influenced microbial community diversity, composition, and putative functions in different seasonal patterns. Microbial communities from a ten-year restoration area and a native mature K. obovata area shared more similarities than other areas. In both seasons, the key environmental factors driving microbial community included total carbon and nitrogen content, the ratio of carbon to nitrogen, and the soil pH. In addition, total sulfur and total phosphorus contents significantly contributed to structuring microbial communities in summer and winter, respectively. This study provides insights into microbial diversity, composition, and functional profiles in association with physicochemical impacts, with the aim of understanding microbial ecological functions during the invasion and restoration processes in wetland ecosystems.