Influence of Simulated Saline Alkaline Conditions on Soil Bacterial Community and Isolations

Saline-alkaline ions including Na⁺, Cl^-, HCO₃^-, and CO₃^2- etc., adversely impact agricultural production by decreasing soil adaptability and function of microbial communities. Until now, most of the studies regarding salinity were mainly focused on sodium chloride and sodium sulfate, seldom concerning the actual saline-alkaline soil conditions. In the current study, we collected saline-alkaline soil samples from three different habitats, and employed six simulated saline-alkaline conditions (encompassing sulfate-type, chloride-type, and soda-type) to enrich soil bacterial communities. Using high-throughput sequencing, we characterized the composition of bacterial communities under distinct enrichment conditions, and isolated strains from the respective soil environments via the single-colony isolation method. The results showed that, regardless of soil sources, bacterial community diversity decreased significantly under conditions where pH ≥ 9.0 and total salinity ≥ 6.0%. Among all tested factors, pH and carbonate ions were the most impactful in shaping bacterial community composition, followed by sodium chloride. This suggests that soda-type saline-alkaline soils exerted the strongest influence on microbial communities. Furthermore, specific microbial taxa responded differently to salt ion compositions. For example, Bacillus and Woeseia genus were positively associated with water-soluble chloride and sodium ions. Additionally, the keystone taxa among the enriched halotolerant bacterial isolates included Bacillus, Halomonas, Clostridioides, Pseudoalteromonas, Zobellella, and Alkaliphilus genus. From sulfate-type saline-alkaline soils, a greater number of bacterial isolates were recovered; however, no isolates could be enriched under condition 6 (pH 10, NaCl 10 g/L, Na₂SO₄ 5 g/L, Na₂CO₃ 5 g/L, salinity 2.0%). These results provided theoretical foundation and potential application guidance for the bio-remediation of saline-alkaline soils.