ICOM1 Abstract

CACERES, ALICIA1 & GISELA CUENCA2. 1Instituto de Biolog’a Experimental, UCV. Apdo. 47114, Caracas 1041, Venezuela. 2Centro de Ecolog’a, IVIC, Apdo. 21827, Caracas 1020-A, Venezuela. -Effects of mycorrhizal associations on growth, photosynthesis and phosphorus response of Clusia minor L Plants in natural ecosystems have varying degrees of dependence on mycorrhizal associations which are the results of inherent properties of the plants themselves and availability of nutrients in the soil in which they naturally occur. The aim of this work was to test if seedlings of Clusia minor (five months old) respond to mycorrhizal inoculation (Scutellospora fulgida) and to P supply in an acid soil (pH: 4.4) and in a neutral soil (pH: 7.1). Nine treatments were performed: Control (NM), mycorrhizal (MYC), Phosphorus (P) (375 mg per kg soil), Phosphorus and MYC (MYC+P) and unsterilized forest soil (F). The results showed that F and NM plants grew significantly less than MYC, MYC+P, and P (P<0.05) in both soils. There are a clear tendency to allocate more biomass to root in NM and F plants in acid soil as compared with treatments in neutral soil. We did not find differences significant among the treatments in neutral soil for some parameters of growth. Although this treatment had the highest weight, it had the lowest mycorrhizal response. The net assimilation rate increased significantly with P fertilization and MYC+P in both soil, whereas a lower response was seen for NM and F plants. The growth response of C. minor in different soils indicated that the mycorrhizal dependence (MD) varies as the P availability of soil changes and the seedlings growing in neutral soil showed the least MD and that support the hypothesis that there are a gradient of dependence in relation to habitat, specially regarding the soil nutrient availability.