Effect of phosphate-solubilizing bacteria and vesicular-arbuscular mycorrhizae on tomato growth and soil microbial activity

The interaction of vesicular-arbuscular mycorrhizae (VAM) and phosphate-solubilizing bacteria (PSB) on plant growth, soil microbial activities, and the production of organic acids was studied in non-sterile soil containing hydroxyapatite and glucose. Glomus etunicatum (VAM), a fungus, and Enterobacter agglomerans, a bacterium able to solubilize insoluble phosphate, were used as inocula. Three treatments and a control were used: inoculation with E. agglomerans (treatment E), inoculation with G. etunicatum (treatment G), inoculation with E. agglomerans+G. etunicatum (treatment E+G) and the control (C). Inoculation with E, G, or E+G had increased plant growth by days 35, 55, and 75 compared with the control. Microbial biomass carbon (C) and alkaline phosphatase activity in the rhizosphere generally increased with time. Alkaline phosphatase activity was higher in treatments G and Et G compared with the control at 35 and 55 days. The highest acid phosphatase activity was observed in treatment E at 35 days; however, this markedly decreased with time. A significantly higher soluble phosphorus (P) concentration was observed in treatments E and E+G on day 55 com pared with C. However, there was no significant difference in soluble P concentration in the rhizosphere between treatments with time. The P concentration was greatest in all treatments on day 55. The highest oxalic acid concen tration was observed in the rhizosphere of the non-sterile soil in E+G on day 35. Total N and P uptake in plants from treatments E and G were higher compared with the control. However the highest N and P uptake was observed in treatment E+G. This study suggests a synergistic interaction between E. agglomerans and G. etunicatum.