PHOSPHORUS UPTAKE BY MYCORRHIZAL AND NONMYCORRHIZAL PINUS ROOTS

Ectomycorrhizae of Pinus caribaea var. hondurensis Morelet with the fungus Pisolithus tinctorius (Persoon) Coker et Couch grown under two different P sources were studied, in an effort to understand the mechanism of P absorption by these symbionts. Mycorrhizal plants yielded significantly more root and top fresh and dry matter, higher Vmax and lower Km and Cmin than the nonmycorrhizal ones. The source of P did not influence significantly these parameters. The results suggest that the increased P uptake by mycorrhizal plants was due to an increase in the number of absorption sites per unit of weight of root and mainly to an increase in the affinity of these sites to P. Moreover mycorrhizal plants, opposite to nonmycorrhizal ones, seem to be able to uptake P from the soil solution when this ion is present in rather low concentrations.