Kosakonia oryziphila KC516 mediated growth promotion of Cosmos bipinnatus in phosphogypsum by modulating rhizosphere geochemistry and root transcriptome

Phosphogypsum (PG), a by-product of phosphoric acid production, is mainly stockpiled, which occupies land and poses pollution risks, necessitating expanded resource utilization. We isolated Kosakonia oryziphila 516 with good acid-producing and phosphate-solubilizing effects from the rhizosphere of Eleusine indica growing on PG, and it can promote the growth of five plant species, with the strongest growth-promoting effect observed in Cosmos bipinnatus. In this study, pot experiments were conducted to investigate the effects of KC 516 on the phenotypic indices, physiological indices, rhizosphere soil properties, and root gene expression of C. bipinnatus grown in PG-based substrate. Our analysis revealed that KC 516 significantly enhanced plant growth, increasing germination rate, plant height, root length, and dry weight by 12%, 28%, 106%, and 115%, respectively. It also elevated photosynthetic pigments and indole-3-acetic acid (IAA) levels while slightly reducing abscisic acid (ABA) and soluble sugars. In the rhizosphere, KC 516 lowered soil pH and decreased Ca²⁺ and SO₄^2- concentrations, concomitantly increasing available phosphorus by 11.4%. Transcriptome analysis revealed that KC 516 upregulated genes involved in hormone regulation, organic acid synthesis, and anion transport, all of which were positively correlated with growth and photosynthetic parameters. Notably, among 35 differentially expressed transcription factor families, MYB-family transcription factors were associated with photosynthetic pigment accumulation, AP2/ERF regulated root development, and bHLH was linked to organic acid synthesis. By facilitating available phosphorus release in PG and enhancing sulfur uptake, KC 516 promotes the growth of C. bipinnatus in phosphogypsum substrate. This growth promotion is associated with altered expression of genes governing growth hormones, organic acid synthesis, and sulfate anion transport in C. bipinnatus. This study provides a theoretical basis and strain resources for expanding the disposal and utilization pathways of PG and the vegetation restoration of PG stockpile areas.