Application of a Pseudomonas strain mitigates the combined stresses of phenolic acids and salt in soil-grown cucumber.

Abstract

As both phenolic acids and salt accumulate in greenhouse soil, soil-grown plants in greenhouses are exposed to both phenolic acid and salt stresses. However, no method for mitigating these combined stresses has been reported for soil-grown plants. In this study, we examined whether bacterial inoculation could alleviate the combined stresses of phenolic acids and salt and facilitate plant productivity in greenhouse. A Pseudomonas strain referred to as CFA was separately inoculated into medium and cucumber-planted soil supplemented with ferulic acid (FA), p-hydroxybenzoic acid (PHBA), and a salt (sodium chloride, sodium sulfate, sodium carbonate, or sodium bicarbonate). CFA showed plant growth-promoting properties and could degrade FA and PHBA in salt-supplemented medium. After application of CFA into FA-, PHBA-, and salt-supplemented soil, CFA colonization was observed, and the levels of malonaldehyde and hydrogen peroxide in the leaves were found to be decreased. Meanwhile, the activities of glutathione peroxidase, ascorbate peroxidase, superoxide dismutase, and catalase in cucumber and those of phosphatase, urease, sucrase, and catalase in soil were increased. Moreover, CFA application to soil improved cucumber growth, reduced FA and PHBA concentrations in soil, enhanced soil polysaccharide contents, and altered the rhizospheric bacterial communities. We thus propose that CFA application affects rhizospheric bacterial communities; it degrades FA and PHBA in soil thus decreasing their concentrations, induces antioxidant enzymes in cucumber, increases the activities of soil enzymes, and enhances soil polysaccharide contents, thus mitigating the combined stresses of FA, PHBA, and salt.