SSSAJ Journal of Natural Resources and Life Sciences Education
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Soil Science Society of America Journal 64:949-955 (2000)
© 2000 Soil Science Society of America

DIVISION S-4-SOIL FERTILITY & PLANT NUTRITION

Mechanism of Calcium and Phosphate Release from Hydroxy-Apatite by Mycorrhizal Hyphae

Ricardo L.Lange Nessa and Paul L.G. Vlekb

a Institute of Agronomy in the Tropics, Grisebachstr. 6, Goettingen 37077, Germany
b Center for Development Research, Univ. of Bonn, Walter-Flex-Str. 3, Bonn 53113, Germany

p.vlek{at}uni-bonn.de

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.

Abbreviations: HA, hydroxy-apatite • PVC, polyvinyl chloride • VAM, vesicular-arbuscular mycorrhiza






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Copyright © 2000 by the Soil Science Society of America.