Pisolithus arhizus ectomycorrhiza affects plant competition for phosphorus between Pinus elliottii and Panicum chamaelonche

 Our objective was to evaluate the ability of an ectomycorrhizal fungus to alter the competitive interaction of pine seedlings growing with grass, and to determine whether the interaction was modified by soil-phosphorus (P) concentration. Slash pine (Pinus elliottii), inoculated with the ectomycorrhizal fungus Pisolithus arhizus or fortuitously colonized by Thelephora terrestris, and a native grass (Panicum chamaelonche) were grown in a greenhouse at three P levels (0.32, 3.22, 32.26 μM H₃PO₄). Pine inoculated with P. arhizus took up more P when competing with the nonmycorrhizal grass than when competing with another pine (irrespective of pine mycorrhizal status). Phosphorus uptake kinetics (C_min, the minimum concentration at which P can be absorbed from a solution; I_max, the maximum uptake rate) for pine and grass were also determined under hydroponic conditions. Pine had a higher I_max than grass but grass had a lower C_min, suggesting that pine is more competitive at higher nutrient concentrations while grass is more competitive at lower nutrient concentrations. The controlled conditions used in these experiments allowed us to evaluate specific parameters (P uptake and absorbing surface area) affecting plant competition. Accepted: 7 August 1999