Distinct Rhizosphere Regulatory Mechanisms of Single Superphosphate and Diammonium Phosphate in Maize Under Saline-Alkali Stress

Background Low phosphorus (P) bioavailability represents a major abiotic constraint on crop productivity in saline-alkali soils. However, the rhizosphere regulatory mechanisms driving divergent plant responses to different P fertilizer sources remain incompletely characterized. Methods Maize was cultivated in rhizobox systems with three treatments, including no P control (CK), single superphosphate (SSP), and diammonium phosphate (DAP). Using an integrated multi-omics approach, we characterized the distinct mechanisms through which the two P fertilizers shape the maize rhizosphere microenvironment. Results A Both SSP and DAP application promoted maize growth, increased P uptake, and enhanced tolerance to saline-alkali stress. Specifically, SSP lowered rhizosphere soil pH, maintained plant K ⁺ /Na ⁺ homeostasis, and stimulated root exudation of metabolites including fructose and citric acid. By contrast, DAP elevated catalase (CAT) activity in plant and alkaline phosphatase (ALP) activity in soil, induced root secretion of sucrose, citric acid, and malic acid, and yielded a larger increase in soil Olsen-P concentration. Of all measured parameters, K ⁺ /Na ⁺ , Olsen-P content, soil microbial community properties, and CAT activity were the dominant drivers of maize P acquisition under saline-alkali conditions. Conclusions SSP and DAP mitigate saline-alkali stress and improve maize P uptake via distinct regulatory pathways, involving the maintenance of ion homeostasis, antioxidant defense modulation, carbohydrate metabolism reprogramming, and rhizosphere microenvironment remodeling. These findings provide a theoretical framework for precision P fertilization and improved P use efficiency in saline-alkali croplands.