CUENCA, GISELA , ZITA DE ANDRADE & ERASMO MENESES.
IVIC, Centro de Ecología, Apartado 21827, Caracas 1020-A, VENEZUELA.
Mycorrhizae can contribute to plant tolerance to soil acidity and toxic metals such as aluminum. In this work we present the results obtained after nine months of simulated acid rain on seedlings of Clusia multiflora, a tropical woody species which naturally grows on an acid soil high in soluble Al. The aim of this work was: a) to evaluate if vesicular-arbuscular mycorrhizae (VAM) could be responsible for the tolerance to acidity and to aluminum of C.multiflora and b) to evaluate if an inoculum of VAM fungi (VAMF) obtained from acid soils contributes more with the tolerance to acidity of C.multiflora than one obtained from neutral soils. Seedlings growing on a sterilized acid soil were inoculated with VAMF isolated from two contrasting edaphic conditions: acid soil and neutral soil. A non-inoculated control was also included. Each one of these treatments was divided in four and watered with solutions of different acidity: distilled water (pH6.5), water at pH 5,4 and 3. Results showed that in absence of VAM, seedlings of C.multiflora did not grow, indicating that this species is highly dependent of VAMF. Acidity affected the growth of plants inoculated with VAMF from neutral soils which showed less ramified roots and a lower shoot-root relationship than those inoculated with VAMF from acid soils. Acidity did not affect the growth of C.multiflora inoculated with VAMF from acid soils. The histochemical analysis of the distribution of Al in roots showed a new finding, namely that aluminum was accumulated in the mycelium of the fungus, mainly in the vesicles and auxiliary cells. We concluded that VAMF contribute to the acidity tolerance of C. multiflora, diminishing the quantity of this element that is absorbed by the roots and translocated to the shoot.