Resalinization Is Associated with Bacterial Alpha Diversity by Influencing Life-History Strategies, and Niche Properties in Coastal Saline Soils

Soil salinization is a critical global limiting factor constraining agricultural productivity. Although soil salinity strongly influences microbial diversity and community composition, the underlying mechanisms regulating microbial diversity remain poorly understood. This work aimed to elucidate the impact of the resalinization process on bacterial alpha diversity in coastal saline soils. Soil samples were collected in the Yellow River Delta, Shandong, China, in March, May, and June, and soil salt content increased from 1.73 to 2.33 g kg−1 over this period. Our results indicate that soil salt content increased significantly across different periods (p < 0.01), exhibiting typical characteristics of soil salinization. Increased soil salinity was accompanied by a lower relative abundance of bacterial phyla with lower rrn copy numbers (low-rrn bacteria) and a higher relative abundance of bacterial phyla with higher rrn copy numbers (high-rrn bacteria) (p < 0.05). Moreover, high salinity was also associated with a decrease in niche breadth (p < 0.05) and an increase in niche overlap (p < 0.001) among high-rrn bacteria, whereas niche breadth increased and niche overlap decreased in low-rrn bacteria (p < 0.01). Consequently, the PLS-SEM (partial least squares structural equation modeling) showed that increasing soil salinity constrained bacterial resource utilization by regulating the niche properties of high- and low-rrn bacteria, thereby reshaping bacterial community structure and ultimately affecting bacterial α diversity. These findings provide a theoretical basis for improving soil microbial functioning by developing biologically based remediation strategies in coastal saline soils.