EVIDENCE ON THE PATHWAYS OF PHOSPHORUS TRANSFER BETWEEN VESICULAR - ARBUSCULAR MYCORRHIZAL PLANTS

Mycorrhizal hyphae can link one root to another, and it is possible that phosphorus passes from plant to plant by these links. We present evidence on whether this 'direct transfer pathway' is the major route between mycorrhizal plants, or whether most phosphorus passes from the roots of one plant to the soil before being taken up by the other plant's roots or its associated mycorrhizal hyphae (the 'soil pool pathway'). The time-course of loss of ³² P from Lolium perenne L. roots to solution was measured after ³² P had been fed to leaves. Another experiment indicated that the amount of ³² P lost to soil was not influenced by mycorrhizal infection. ³² P was applied to soil in which Plantago lanceolata L., mycorrhizal or non-mycorrhizal, was growing and the time-course of uptake determined. Using these results, two alternative models, the 'direct transfer model' and the 'soil pool model', were used to predict the time-course and amount of ³² P transfer from L. perenne to P. lanceolata. The predictions were then compared with measured transfers between these two species presented here and in a previous paper. The soil pool model's predictions of both amount and time-course of transfer gave the better fit to observation. The evidence thus suggests that direct hyphal links between roots are not important in phosphorus transfer between these plants.