Mycorrhizal Mediation of Phosphorus Availability: Synthetic Iron Chelate Effects on Phosphorus Solubilization

To determine whether chelation of Fe in slightly acidic soils will release sufficient P from Fe phosphate complexes to stimulate plant growth in P‐limited soils, the effect of EDDHA {ethylenediamine [di( o ‐hydroxy‐phenylacetic) acid]}, a strong synthetic Fe‐chelating compound, on plant growth was studied in two P‐deficient native prairie soils and a P‐rich agricultural soil. Under laboratory conditions, EDDHA increased P extractability in the three soils. Subsequently, in a prairie soil/water slurry, repeated application of 10 −4 M EDDHA significantly increased big bluestem ( Andropogon gerardii Vitman) growth and P uptake as compared with distilled water controls or slurries which received only a single application of 10 −3 M EDDHA. In slurries prepared with agricultural soil, growth of big bluestem was not affected by either concentration of the EDDHA. When the effect of EDDHA on growth of mycorrhizal and nonmycorrhizal plants was compared, in the prairie soils without EDDHA, mycorrhizal plants were significantly larger than nonmycorrhizal plants. Mycorrhizal plants in EDDHA‐amended soil had significantly greater growth and P uptake than mycorrhizal plants in unamended soil. However, neither concentration of EDDHA affected growth of nonmycorrhizal plants. In agricultural soil, plant growth was not affected by the mycorrhizal fungus or the EDDHA amendment. It appears that siderophore production by mycorrhizae or other soil microbes can significantly increase P availability in low pH soils and that this is a feasible mechanism by which mycorrhizal plants could assess P sources unavailable to nonmycorrhizal plants.