Soil profile rather than reclamation time drives the mudflat soil microbial community in the wheat-maize rotation system of Nantong, China

Purpose Conversion of coastal mudflats to agricultural soil is one of the most important land use practices in Eastern China. However, effects of soil profile and reclamation time on soil microbial community, which play an important role in soil nutrient cycling, are still poorly documented. Materials and methods Soil profile (0-15 cm, 15-30 cm, 30-45 cm) samples were collected from four sites with different reclamation ages (R12: 12 years, R38: 38 years, R68: 68 years, R100: 100 years) in Rudong County, Nantong, Jiangsu, China. Soil bacterial communities were determined via Illumina 16S rRNA gene high-throughput sequencing. Results and discussion Soil electrical conductivity (EC) responded more rapidly to reclamation time than soil pH. Soil total carbon and nitrogen increased with increasing reclamation age. Soil available nutrients (ammonium, nitrate, dissolved organic carbon, and available phosphorus) were affected by the agricultural practice and did not show a unanimous tendency between different reclaimed sites. Proteobacteria, Acidobacteriota, and Bacteroidota dominated the bacterial community across different sites and soil profiles. However, Methylomirabilota- and Nitrospirota-associated species, which are involved in nitrogen cycling, increased with increasing soil depth. Canonical correspondence analysis (CCA) showed that bacterial community was grouped by soil depth and also significantly affected by soil pH, EC, and reclaimed time. Moreover, co-occurrence network analysis showed a potential role of low abundant phyla besides dominant phyla in stabilizing the bacterial community, and the connection between soil properties and bacterial amplicon sequence variant (ASV) numbers would shift along soil profiles. Conclusions Reclamation time of the coastal mudflats is not the only reason for the shift of bacterial community. Here, we found soil profile had a strong influence on soil bacterial composition in the coastal reclaimed wheat-maize rotation soils.