Nitrate uptake in maritime pine (Pinus pinaster) and the ectomycorrhizal fungus Hebeloma cylindrosporum: effect of ectomycorrhizal symbiosis

Nitrate uptake rates were determined for nonmycorrhizal and mycorrhizal maritime pine (Pinus pinaster) associated with the ectomycorrhizal basidiomycete Hebeloma cylindrosporum and for this fungal species grown in vitro. Different [NO3−] (0–1.3 and 10 mM) were supplied to nonmycorrhizal or mycorrhizal P. pinaster plants grown axenically in test tubes for 21 weeks. Uptake of NO3− by the plants was determined by measuring NO3− depletion from the medium that was added to the culture tubes without root pertubation. For all applied [NO3−] the uptake rates for NO3− in mycorrhizal plants were increased about twofold compared with nonmycorrhizal plants. The same range of [NO3−] was supplied to the fungus in pure culture, and uptake rates were calculated either from the measurement of NO3− depletion from the medium or by 15N accumulation in the mycelium. For the same external nitrate concentrations the results obtained with these two methods were not significantly different. The amount of fungal biomass in mycorrh...