Influence of stand age on sediment bacterial communities in restored mangrove forests

Microbes in mangrove sediments provide essential ecological functions, acting symbiotically with their mangrove hosts. Investigating their dynamics in restored mangroves over a chrono-sequence offers valuable indications on how microbial diversity is shaped by both restored mangrove age and environmental factors. In this study, we examined the dynamics of the bacterial community and sediment properties in four Rhizophora apiculata forests restored at different times, as well as the sediments of an intact Avicennia marina forest. The result indicated that higher diversity and abundance in older restored mangroves were supported by higher nutrients in sediment, particularly carbon content (ANOVA, p < 0.01). The most dominant bacterial phylum Proteobacteria, showed decreasing relative abundance with sediment depth, while Chloroflexota exhibited increasing relative abundance. The bacterial community demonstrated a strong correlation with sediment properties, especially salinity and carbon content. Co-occurrence network analysis revealed increasing module counts in younger restored mangrove forests, with stabilised counts observed at the 9 years suggesting established bacterial functional dynamics by this age. Random attack of network analysis also indicated that the 5- and 9-year-old mangrove forests were more fragile, while the 16 year-old mangrove forests displayed lowest resilience due to higher salinity levels. In contrast, the 21-year-old restored mangrove and intact A. marina exhibited robust and well-connected networks. In summary, older R. apiculata restored forests fostered enhanced soil nutrient content, especially surface sediment carbon content, and supported a more stable, diverse bacteria community network.