Succession of bacterial community composition in coastal agricultural soils along a 1000-year reclamation chronosequence in Hangzhou Bay, China

Soil bacterial successional trajectories under frequently disturbed circumstances (such as agricultural practice) are less known due to the complexity and uncertainty of disturbance. Here, a reclaimed coastal soil chronosequence spanning over a millennium was studied to understand the variation in soil microorganisms. We used 16S rRNA gene-based quantitative PCR to determine bacterial number and Illumina Sequencing to analyse bacterial community composition and diversity. Despite 10-fold higher 16S rRNA gene copy number, coastal sediments showed the lowest bacterial phylogenetic diversity, demonstrating that bacteria acclimatised in the destination environment with low nutrient and high salinity. Among the reclaimed soil, regular variation in microbial distribution (abundance and diversity) and the "disturbance climax" theory can explain the dynamics of bacterial succession. Consistent with soil physicochemical variables, bacterial community varied in an orderly way and changed more drastically at initial stage (early 60 years) but only slightly fluctuated thereafter. The soil variables soil organic matter (SOM), total nitrogen (TN), and electrical conductivity (EC) were confirmed to be the main factors affecting bacterial succession, among which SOM played a dominant role in initial and long-term reclamation stage (500 similar to 1000 years), while TN was more important in mid-term reclamation (5 similar to 280 years).