Beschreibung:
The role of vesicular‐arbuscular mycorrhiza (VAM) in facilitating the uptake of sparingly soluble nutrients from the soil has been well documented. Uncertainty remains regarding the mechanism controlling the dissolution of tightly bound P such as in phosphate rock. We studied the differential Ca and P uptake by the external mycelium of VAM in maize (Zea mays L.) grown in an acid tropical soil supplied with hydroxy‐apatite (HA). Three experiments were conducted in modified double‐pot systems where Ca was adequately provided through a nutrient solution and P in the form of apatite through a compartment only accessible to the hyphae. The results showed that in this system: (i) plant uptake of the apatite P occured only with VAM formation, (ii) the P release from the apatite was accompanied by a stochiometrically equivalent buildup of exchangeable Ca in the hyphal compartment, and (iii) the released apatite P was quantitatively recovered by the maize . It appears that the hyphae drove the apatite dissolution by mass action through the selective absorption of P, thereby overcoming the counter‐ion effect due to the Ca accumulation in the soil.