Ectomycorrhizal (ECM) fungi form mutualistic symbioses with trees in boreal and north temperate forests and have key roles in regulating biogeochemical cycles. The extensive mycelium produced by many ECM fungi enables resources to be transported over large distances. Some ECM fungi are considered to be specialists and have a restricted range of host plant species whilst others are considered generalists and can form mycorrhizas with a number of species. Little is currently known about the reasons why specialist and generalist mutualists have evolved and so this project aims to investigate the basis for these different strategies. The resource stoichiometry between plant and fungal partners was predicted to be a key factor: specialist fungi may be more efficient in obtaining nutrients from litter and transporting these rapidly to host plants and in return may receive larger amounts of plant photosynthate. Here, stable and radioisotopes were used to trace and quantify transfer of carbon and phosphorus, and fine-scale spatial-temporal analysis of amino acid transportation between host plants and fungi. The photon-counting scintillation imaging (PCSI) was used to show the amino acid was transported long-distance by ECM fungi intact and that the transportation was highly directional but the speed of transfer varies between species of ECM. The transportation of amino acid and phosphorus from generalist fungus to the host plant was rapid compared to the specialist fungus.