Potassium-solubilizing rhizobacteria enhance K⁺/Na⁺ homeostasis and antioxidant defenses in cotton seedlings under salinity

Soil salinity severely restricts cotton production in arid regions by limiting potassium (K) availability and disturbing K⁺/Na⁺ homeostasis. Although potassium-solubilizing plant growth-promoting rhizobacteria (PGPR) offer a promising strategy, the mechanistic links between microbial K solubilization, ion regulation, antioxidant responses and growth remain poorly defined. We isolated a salt-tolerant potassium-solubilizing strain, Pseudomonas aeruginosa A10 rhizobacteria, from saline–alkaline gray desert soil and evaluated its effects on cotton using five NaCl levels (0, 100, 300, 500, 700 mM) in vitro and three salinity treatments (0, 100, 200 mM) in pot experiments. P. aeruginosa maintained robust growth up to 500 mM NaCl and retained > 50 % of its non-saline K-solubilizing capacity. It secreted substantial amounts of lactic, citric, acetic and succinic acids, mobilizing mineral-K and increasing water-soluble and exchangeable K. In seedlings, inoculation improved germination, increased plant height by 22–38 %, total chlorophyll content by ∼21 %, and shoot and root biomass by 15–51 %. It enhanced K⁺ uptake (16–22 %), reduced Na⁺ accumulation (14–34 %), and raised the K⁺/Na⁺ ratio by 55–75 %. P. aeruginosa also strengthened antioxidant defenses, with activities of peroxidase, superoxide dismutase and catalase activities increasing by 14–85 % and malondialdehyde content and superoxide anion levels decreasing by 16–34 %. Random-forest and PLS-PM analyses identified soil K availability (water-soluble and exchangeable K), ionic rebalancing and antioxidant activation as the central pathways driving growth improvement. Overall, P. aeruginosa alleviates salt stress through a coordinated “K solubilization–ion homeostasis–antioxidant defense” mechanism, offering a biologically based approach to enhance cotton resilience, reduce reliance on chemical K fertilizers, and improve soil health in saline–alkaline farming systems.