Abstract
Plants grown at reduced photon irradiances have a reduced growth response to mycorrhizal infection over non-mycorrhizal controls. Although phosphate inflow is reduced with reduced photon irradiance (and even becomes negative in plants grown at 20 μmol m
−2 s
−1), the reduced growth response is not due to a P starvation of plants, as all mycorrhizal plants were sufficient in P. This was largely because the plants were still influenced by phosphate stored in the seed. It is likely that the decreased growth response with decreased photon irradiance is due to an increased significance of the carbohydrate drain by the fungus.