Nitrogen and phosphorus acquisition by the mycelium of the ectomycorrhizalfungus Paxillus involutus and its effect on host nutrition

The contribution of the extramatrical mycelium to N and P nutrition of myco rrhizal Norway spruce (Picea abies (L.) Karst.) was investigated. Seedlings either inoculated with Paxillus involutus (Batsch) Fr. or non-mycorrhizal were grown in a two compartment sand culture system where hyphae were separ ated from roots by a 45 mu m nylon net. Nutrient solution of the hyphal com partment contained either 1.8 mM NH4+ and 0.18 mM H2PO4- or no N and P. Alu minium added to the hyphal compartment as a tracer of mass flow was not det ected in the plant compartment, indicating that measurements of N and P tra nsfer by the mycelium were not biased by solute movement across the nylon n et. The addition of N and P to the hyphal compartment markedly increased dry we ight, N and P concentration and N and P content of mycorrhizal plants. Calc ulating uptake from the difference in input and output of nutrient in solut ion confirmed a hyphal contribution of 73 %, and 76 %, to total N and P upt ake, respectively. Hyphal growth was increased at the site of nutrient solu tion input.