Local measurements of nitrate and potassium fluxes along roots of maritime pine.: Effects of ectomycorrhizal symbiosis

In order to assess the actual role of ectomycorrhizae in ion uptake by the ectomycorrhizal root system, we used a microelectrode ion flux estimation methodology that provided access to local values of net fluxes. This made it possible to investigate the heterogeneity of ion fluxes along the different types of roots of Pinus pinaster associated or not with ectomycorrhizal species. We compared two fungi able to grow with nitrate in pure culture, Rhizopogon roseolus and Hebeloma cylindrosporum, the former having a positive effect on host tree shoot growth (c. +30%) and the latter a negative effect (c. -30%). In non-mycorrhizal plants (control), NO3- was taken up at higher rates by the short roots than by the long ones, whereas K+ uptake occurred mainly in growing apices of long roots. In mycorrhizal plants, H. cylindrosporum did not modify K+ uptake and even decreased NO3- uptake at the level of ectomycorrhizal short roots, whereas R. roseolus strongly increased K+ and NO3- fluxes at the level of ectomycorrhizal short roots without any modification of the fluxes measured along the fungus-free long roots. The measurement of ion influxes at the surface of the ectomycorrhizal roots can provide a way to reveal actual effects of mycorrhizal association on ion transport in relation to mycorrhizal efficiency in natura conditions.