Variation of bacterial community diversity and composition in saline-alkali soils reclaimed with flood irrigation and crop cultivation is driven by salinity and edaphic factors.

Reclamation is crucial for improving the fertility and productivity of saline-alkali soils, but the evolution of soil bacterial communities during the course of reclamation, which is an important feedback of soil micro-ecosystem, has received little attention. This study was conducted to investigate the variation of bacterial community diversity and composition in reclaimed saline-alkali soils based on space-for-time substitution, elucidate the underlying ecological mechanisms of bacterial community assembly processes, and identify the key driving factors of bacterial community evolution. The soil bacterial communities in undeveloped saline-alkali land and farmlands with different reclamation history (1-4, 5-6, and 10-25 years) in the Yellow River Delta, China, was analyzed by 16S rRNA gene amplicon sequencing. Soil bacterial diversity was found to increase significantly with reclamation history, and the entire bacterial community composition varied remarkably in the saline-alkali soils at different stages of reclamation. Halophilic and halotolerant bacteria dominated in the soils of undeveloped saline-alkali land (33.7 %), but their abundance diminished largely in the reclaimed soils. Analysis of bacterial community assembly processes suggested that heterogeneous selection dominated the change of bacterial communities in the saline-alkali soils that had been reclaimed for 1-4 years (52.8 %), 5-6 years (93.1 %), and 10-25 years (94.4 %). Salinity, soil organic carbon, pH, and moisture content were found to be the key environmental factors driving the evolution of bacterial communities in the reclaimed saline-alkali soils. While salinity directly shaped the bacterial community diversity, the other key drivers primarily governed the composition of bacterial communities in the saline-alkali soils during reclamation. These findings shed light on the probable ecological mechanisms of assembly processes and the environmental factors driving the soil bacterial communities during reclamation of saline-alkali lands, which could help better understand the evolution of soil bacterial communities under declining saline stress and optimize strategies to improve the agroecosystem health of saline-alkali lands.