THE USE OF INOSITOL HEXAPHOSPHATE AS A PHOSPHORUS SOURCE BY MYCORRHIZAL AND NONMYCORRHIZAL SCOTS PINE (PINUS-SYLVESTRIS)

1. The external mycelia of the ectomycorrhizal fungi Thelephora terres tris and Suillus luteus, associated with Pinus sylvestris roots, exhib ited a substantial extracellular acid phosphatase activity, The activi ty 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 bio mass at a low P-i nutrition level. 3. The phytase activity of the exte rnal mycelia could not be detected; at the root surface a phytase acti vity was observed. Mycorrhizas had significantly higher activities tha n uninfected roots. 4. The addition of a relatively high concentration of a soluble phytate to the growth substratum resulted in an increase d relative growth rate (RGR) in both mycorrhizal and non-mycorrhizal p lants. The influence of the mycorrhizal fungi on the use of the phytat e-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 hypo thesis that phytate, which has a low solubility in soils, is a useful P source for ectomycorrhizal plants.