Soil phosphate availability drives shifts between arbuscular mycorrhizal and ectomycorrhizal fungi in the dual mycorrhizal plant Quercus serrata.

Dual mycorrhizal plants are associated with both arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) fungi that differ in cost and effectiveness for nutrient acquisition. Little is known about environmental drivers for the shifts between these associations in dual mycorrhizal plants. We hypothesize that high phosphate availability leads to increases in AM fungal association that may be less costly than EcM fungal association. Root, soil, and leaf samples of the dual mycorrhizal plant Quercus serrata were collected from 15 field sites differing in available phosphate across Japan. The fungal internal transcribed spacer region of DNA extracted from the roots was amplified and sequenced. Chemical properties of the soil and leaf samples were analyzed. AM fungal richness and abundance were positively correlated with NaOH-extractable phosphate (NaOH-Pi) in the soil, whereas the abundances of short- and long-distance explorer-type EcM fungi were correlated negatively and positively, respectively, with inorganic N to NaOH-Pi ratios. These results imply that phosphate availability drives EcM-AM shifts, as well as that in the exploration types of EcM fungi. We demonstrated that dual mycorrhizal plants flexibly accommodate the distinctive mycorrhizas in response to soil nutrients, which might be important traits to optimize the cost-benefit ratios for nutrient acquisition in a given environment.