The use of inositol hexaphosphate as a phosphorus source by mycorrhizal and non-mycorrhizal Scots Pine (Pinus sylvestris)

1. The external mycelia of the ectomycorrhizal fungi Thelephora terrestris and Suillus luteus, associated with Pinus sylvestris roots, exhibited a substantial extracellular acid phosphatase activity, The activity was positively correlated with the ergosterol concentration in the growth substratum and decreased with an increasing P nutrition. 2. The pioneer species T. terrestris grew best at a high P-i nutrition level whereas S. luteus, a 'late-stage' mycobiont, produced more active biomass at a low P-i nutrition level. 3. The phytase activity of the external mycelia could not be detected; at the root surface a phytase activity was observed. Mycorrhizas had significantly higher activities than uninfected roots. 4. The addition of a relatively high concentration of a soluble phytate to the growth substratum resulted in an increased relative growth rate (RGR) in both mycorrhizal and non-mycorrhizal plants. The influence of the mycorrhizal fungi on the use of the phytate-P was small, despite the phytase activity of the mycorrhizal feeder roots. 5. The addition of phytate fixed on a HPLC resin did not result in an increase of the RGR and P uptake neither in the non-mycorrhizal nor in the mycorrhizal Pines. The experiment did not support the hypothesis that phytate, which has a low solubility in soils, is a useful P source for ectomycorrhizal plants.