Effects of Reclaimed Water Irrigation on Soil Properties and the Composition and Diversity of Microbial Communities in Northwest China

Reasonably using reclaimed water (RW) for irrigation can help to alleviate water scarcity, while also providing both environmental and economic benefits. However, there is limited information regarding the potential impact of RW irrigation on the nutrients of saline–alkali soils and their microbial communities. This study investigates the effects of RW irrigation on saline–alkali soil properties and microbial communities using a 16S rRNA sequence analysis. The results show that the pH and electrical conductivity (EC) are significantly lower in RW treatment (p < 0.05). Compared to the saline–alkali soil that was not irrigated with RW (CK), the EC value decreased by 42.15–45.76%, in both 0–20 cm and 40–60 cm depth. RW exhibited a significant increase in the abundance of Actinobacteria (32.32–33.42%), Chloroflexi (7.63–15.79%), Firmicutes (9.27–10.42%), and Ascomycota (89.85–95.95%). Bacterial richness and diversity were significantly enhanced after RW irrigation (p < 0.05). At the genus level, the dominant bacterial genera included Bacillus, Penicillium, Aspergillus, and Talaromyces. Differences in the microbial community were observed between the two treatments and among soil depths within each treatment (p < 0.05). A network analysis indicated that the internal relationships among bacterial communities become more complex following RW irrigation, whereas the internal connections within fungal communities tend to become more simplified. A redundancy analysis (RDA) showed that soil microbial communities were directly influenced by EC, total nitrogen (TN), and available potassium (AK). Partial least squares path modeling (PLS-PM) results indicated that soil salinity and available nutrients were the most significant factors influencing the microbial community structure. Together, these results indicate that RW irrigation has a positive impact on ameliorating soil salinity and enhancing microbial community diversity in saline–alkali soils. These findings provide valuable insights for the future agricultural utilization of saline–alkali land.