Phosphorus solubilization and pH changes as a result of the interactions between soil bacteria and arbuscular mycorrhizal fungi on a medium containing NO3- as nitrogen source

The interactions between arbuscular mycorrhizal fungi and bacteria may affect the nutrient dynamics in the environment. To study these changes, assays were conducted in a two-compartment Petri plate system. A NO3--N medium containing an insoluble phosphate (P) source was used to evaluate the effect of Glomus intraradices (Schenck & Smith) external mycelium, mycorrhizal, and nonmycorrhizal transformed carrot roots (Daucus carrota L.), alone or in interaction with Pseudomonas aeruginosa (Schroeter) Migula, Pseudomonas putida (Trevisan) Migula, or Serratia plymuthica (Dyar) Bergey et al., on phosphorus solubilization and pH changes of the medium. In the NO3--containing medium, G. intraradices external mycelium as well as the three bacterial species studied were rather inefficient P solubilizers when growing individually. However, when G. intraradices external mycelium interacted with either P. aeruginosa or R putida, the levels of soluble P in the medium significantly increased (P less than or equal to 0.05). These improvements were closely related to changes in the pH of the medium.