Castor bean growth and rhizosphere soil property response to different proportions of arbuscular mycorrhizal and phosphate-solubilizing fungi

A pot culture experiment was performed to study the effects of infection with different proportions of arbuscular mycorrhizal fungus (AMF) and phosphate-solubilizing fungus (PSF) on the rhizosphere soil property of castor bean (Ricinus communis L.). One AMF, Glomus mosseae, and one PSF, Mortierella sp. (Ms), were applied to non-sterilized coastal saline soil. The plant dry mass, leaf chlorophyll content, and P-uptake of castor bean were assessed. In coastal saline soil, the different proportions of both fungi-inoculated seedlings showed significantly greater shoot and root dry weight than the controls, which had lower root-to-shoot ratios than the inoculated seedlings. An increase in phosphorus (P) and chlorophyll contents was also observed in the inoculated seedlings compared with the controls. The appropriate Ms proportion seemed to be advantageous for AMF colonization. However, available P content of fungi-treated soil increased in proportion to the increase in Ms population and AMF colonization. By contrast, the pH of inoculated soil decreased because of the increased proportion of Mortierella, and electrical conductivity values showed a negative correlation with AMF colonization. Soil enzyme activities (i.e., urease, invertase, neutral phosphatase, and alkaline phosphatase) and soil organic matter were also stimulated by inoculation with different proportions of both fungi. However, the catalase activities of inoculated soil were inhibited compared with those of the control soil. Results from this study prove that castor bean planting associated with an appropriate proportion of AMF and PSF will benefit the amelioration of coastal saline soils of eastern China.