Prokaryotic Microbial Diversity and Community Assembly in Reclaimed Coastal Agricultural Soils

Coastal reclamation profoundly alters soil physicochemical conditions and strongly influences soil microbial ecology; however, the millennial-scale successional patterns and assembly mechanisms of prokaryotic communities under such long-term disturbance remain insufficiently understood. In this study, we investigated archaeal and bacterial communities in the plow layer along a 0-1000-year coastal reclamation chronosequence on the southern shore of Hangzhou Bay. We analyzed community abundance, diversity, composition and assembly processes, and quantified the relative contributions of geographic distance, environmental factors and reclamation years to microbial biogeographic patterns. The results showed that reclamation markedly drove continuous soil desalination, acidification, nutrient accumulation, and particle-size refinement. Bacterial abundance exhibited a sharp decline during the early stages of reclamation, whereas archaeal abundance remained relatively stable. The α-diversity of both archaea and bacteria peaked at approximately 210-230 years of reclamation. Community assembly processes differed substantially between the two microbial domains: the archaeal communities were dominated by stochastic processes (77.78%) identified as undominated processes and dispersal limitation, whereas bacterial communities were primarily shaped by deterministic processes (70.75%) driven as variable selection. Distance-decay analysis indicated that bacterial communities were more sensitive to environmental gradients. Multiple regression and variance partitioning further demonstrated that soil pH and electrical conductivity were the key drivers of community structure. Overall, this study reveals the millennial-scale community dynamics and assembly mechanisms of archaea and bacteria in response to coastal reclamation, providing mechanistic insights into long-term microbial ecological succession and offering valuable guidance for sustainable agricultural management and ecological restoration in reclaimed coastal regions.