Effects of Phosphogypsum and Suaeda salsa on the Soil Moisture, Salt, and Bacterial Community Structure of Salinized Soil

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The improvement of saline soil is an important issue that cannot be ignored in the farmland soil environment. The change in soil salinity will inevitably affect the soil bacterial community. This experiment was based on moderately saline soil in the Hetao Irrigation Area, conducted by applying phosphogypsum (LSG), interplanting Suaeda salsa with Lycium barbarum (JP) and applying phosphogypsum and interplanting S. salsa with L. barbarum (LSG+JP),and the local unimproved soil of a L. barbarum orchard was used as the control (CK), to explore the effects of different improvement methods on soil moisture, salinity, nutrients, and bacterial community structure diversity during the growth period of L. barbarum. The results showed that compared with that under CK, the LSG+JP treatment significantly decreased the soil EC value and pH value from the flowering stage to the deciduous stage (P<0.05), with an average decrease of 39.96% and 7.25%, respectively; the LSG+JP treatment significantly increased soil organic matter (OM) and available phosphorus (AP) content during the whole growth period (P<0.05), with an average annual increase of 81.85% and 203.50%, respectively. The total nitrogen (TN) content was significantly increased in the flowering and deciduous stages (P<0.05), with an annual average increase of 48.91%. The Shannon index of LSG+JP in the early stage of improvement was increased by 3.31% and 6.54% compared with that of CK, and the Chao1 index was increased by 24.95% and 43.26% compared with that of CK, respectively. The dominant bacteria in the soil were Proteobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria, and the dominant genus was Sphingomonas. Compared with that in CK, the relative abundance of Proteobacteria in the improved treatment increased by 0.50%-16.27% from the flowering stage to the deciduous stage, and the relative abundance of Actinobacteria in the improved treatment increased by 1.91%-4.98% compared with that in CK in the flowering and full-fruit stages. Redundancy analysis (RDA) results showed that pH, water content (WT), and AP were important factors affecting bacterial community composition, and the correlation heatmap showed that Proteobacteria, Bacteroidetes, and EC values were significantly negatively correlated (P<0.001); Actinobacteria and Nitrospirillum were significantly negatively correlated with EC values (P<0.01). In conclusion, the application of phosphogypsum and interplanting S. salsa with L. barbarum (LSG+JP) could significantly reduce soil salinity, increase nutrients, and improve the diversity of soil bacterial community structure, which is beneficial to the long-term improvement of saline soil in the Hetao Irrigation Area and the maintenance of soil ecological health.