Variations in soil biological properties in poplar plantations along coastal reclamation stages

Mudflat reclamation has changed the ecological environment and soil properties in coastal areas. However, the variations in soil biological properties in areas with a history of coastal reclamation are still poorly understood. We studied the variations in chemical properties, soil microbial biomass carbon (SMBC), nitrogen (SMBN), and phosphorus (SMBP), soil microbial enzyme activity, and soil bacterial diversity in one tideland (native land) and four reclamation stages (reclaimed for 7, 22, 42, and 62 years). With the increase in reclamation time, soil salinity and pH decreased significantly, and the concentrations of soil organic carbon (SOC), total nitrogen, and total phosphorus increased. The concentrations of SMBC, SMBN, and SMBP and the activities of soil β-glucosidase, invertase, urease, and alkaline phosphatase continuously increased with the increase in reclamation time. The diversity and composition of soil bacteria exhibited less variation in natural grasslands (reclaimed for 7 years) compared with tidelands, and the diversity of soil bacteria was significantly higher in poplar plantations (reclaimed for 22, 42, and 62 years) compared with tidelands. The composition of soil bacteria in poplar plantations significantly differed among 22, 42 and 62-year reclaimed land, but no significant difference was observed between 42 and 62-year reclaimed lands. Compared with tideland, in the poplar plantations, the relative abundance of Proteobacteria and Actinobacteria decreased significantly, and the relative abundance of Acidobacteria increased by 391% - 468%. Bacterial communities showed nonrandom co-occurrence and modular patterns in the reclaimed land. Geodermatophilaceae, Bradyrhizobiaceae, Acidimicrobineae_incertae_sedis, and Reyranella were identified as the keystone taxa in the bacterial co-occurrence network. Multivariate regression tree analysis showed that variations in soil salinity and SOC were the key driving factors affecting soil bacterial diversity and community composition along the reclamation stages. Our study showed that the microbial properties of the topsoil layer in poplar plantations continuously improved in reclaimed coastal land. © 2020 Elsevier B.V.