• saprotrophic soil microorganisms;
  • Pisolithus tinctorius;
  • ectomycorrhizal fungus;
  • Pinus resinosa;
  • red pine;
  • nutrition;
  • interactions;
  • synergism


  • • 
    The influence of interactions between the mycorrhizal fungus, Pisolithus tinctorius , and saprotrophic organisms on nutrient transfer to host red pine ( Pinus resinosa ) seedlings is presented here.
  • Red pine seedlings were grown axenically, and with P. tinctorius and forest-floor microbes (both individually and in combination), in two experiments varying in nitrogen availability. Root and shoot growth, as well as tissue nitrogen and phosphorus content, were analyzed after harvesting.
  • At low nitrogen availability, forest-floor microbes, but not P. tinctorius , significantly reduced seedling nitrogen content. Moreover, P. tinctorius did not ameliorate this negative effect. However, seedling phosphorus content increased with forest-floor microbes and P. tinctorius individually, and these combined to give an additive effect. Forest-floor microbes and P. tinctorius , individually, significantly increased seedling nitrogen and phosphorus contents at high nitrogen availability, interacting to give additive and synergistic effects on nitrogen and phosphorus content, respectively.
  • The effect of ectomycorrhizal fungi on host-plant nutrition might depend strongly on the nutrient status of coexisting saprotrophic soil microbes. When nutrients are not limiting, their beneficial effects on host nutrition may be additive or synergistic.