Interdependence of phosphorus, nitrogen, potassium and magnesium translocation by the ectomycorrhizal fungus Paxillus involutus

Translocation is shown of phosphorus, nitrogen, potassium and magnesium to a P-deficient host from ectomycorrhizal fungal hyphae. Mycorrhizal (with Paxillus involutus) and nonmycorrhizal P-deficient spruce (P. abies) seedlings were grown in a two-compartment sand-culture system. Hyphal translocation of nutrients from the inner compartment (penetrated on ly by hyphae) to the host was measured using mass balance (for N, P and K) or stable isotope (N-15 and Mg-25) methods. Addition of P to the hyphal compartment strongly stimulated hyphal growth, and this also increased both seedling P status and growth. Hyphae transloca ted nonlimiting elements in addition to P, contributing 52, 17, 5 and 3-4%, respectively, to total P, N, K or Mg plant uptake. The potential role of t he ectomycorrhizal mycelium in K acquisition was demonstrated. Translocatio n to mycorrhizal seedings of N, K and Mg was strongly reduced when hyphal P -fluxes ceased; this translocation of nonlimiting nutrients depended on sim ultaneous translocation of P. The ectomycorrhizal mycelium has an active role in P acquisition from sourc es not available to roots. Nutrient fluxes within fungal hyphae are interde pendent and strong coupling of N, K and Mg fluxes with long-distance P tran slocation in the mycorrhizal mycelium occurs.