Stand age-related effects of mangrove on archaeal methanogenesis in sediments: Community assembly and co-occurrence patterns.

Mangrove sediment is a key source of methane emissions; however, archaea community structure dynamics and methanogenesis activities during long-term mangrove restoration remain unclear. In this study, microcosm incubations revealed a substantial reduction in microbial-mediated methane production potential from mangrove sediments with increasing stand age; methane production rates decreased from 0.42 ng g d in 6-year-old stands to 0.23 ng g d in 64-year-old stands. High-throughput sequencing revealed a reduction in community diversity because of specific microorganism colonization and species loss, notably a decline in the relative abundance of Bathyarchaeia in sediments of 64-year-old stands. In addition, mangrove sediments, especially those in older stands (20- and 64-year-old), had more complex and stable co-occurrence microbial networks than mudflats. Furthermore, archaea community assembly in older stands was dominated by stochastic processes wherein dispersal limitation was prominent, and that in younger stands (6- and 12-year-old) was driven by deterministic processes. The proportion of dispersal limitation of Bathyarchaeia and traditional methanogens in sediment decreased with an increase in stand age. Quantitative polymerase chain reaction analysis confirmed a decrease in Bathyarchaeia (from 3.50 to 0.54 copies g) and mcrA gene (from 3.83 to 0.25 copies g) abundance in mangrove sediments with an increase in stand age. These findings demonstrate the critical role of Bathyarchaeia in methanogenesis; the decline in microbial interactions and abundance, and the reduced proportion of dispersal limitation of Bathyarchaeia and traditional methanogens collectively contributed to the mitigation of microbial-mediated methane production potential in older mangrove stands.