SPATIAL-DISTRIBUTION OF ECTOMYCORRHIZAS AND ARBUSCULAR MYCORRHIZAS INKORUP NATIONAL-PARK RAIN-FOREST, CAMEROON, IN RELATION TO EDAPHIC PARAMETERS

The frequent co-occurrence of ectomycorrhizas and arbuscular mycorrhiz as in the same ecosystem raises the question about how two functionall y different mycorrhizal associations exploit a spatially heterogeneous habitat. Horizontal (in plots along a transect of 3750 m crossing for est types of low and high abundance of ectomycorrhizal (ECM) host spec ies) and vertical (across profiles of litter and 0-5 cm, 10-15 cm, 25- 35 cm soil layers) distribution of ectomycorrhizas and arbuscular myco rrhizas in relation to edaphic parameters (pH, moisture, total carbon, total nitrogen and extractable-phosphorus concentration) was compared in Korup National Park rain forest, to test the hypothesis that the t wo types of mycorrhiza exploit different niches. No pattern was observ ed in either ECM or arbuscular mycorrhizal (AM) fractional colonizatio n with depth in the profile even though most of the variation in soil parameters was vertical. Only local (between monoliths within plots) h orizontal differences were found in soil parameters. By contrast, hori zontal differences in fractional colonization were found between fores t types, and between monoliths, for ectomycorrhizas but only between m onoliths for arbuscular mycorrhizas. The lack of a clear relationship between both horizontal and vertical distribution of ECM and AM fracti onal colonization and soil parameters suggests that both fungal groups are equally able to colonize the same niche, at the scale of our expe riment. By contrast, a negative relationship was found between AM and ECM fractional colonization in the litter and 0-5 cm and 10-15 cm soil layers. This, in addition to the more heterogeneous horizontal distri bution of arbuscular mycorrhizas in forest areas dominated by ectomyco rrhizas and a patchy vertical distribution of the former as opposed to a more coherent distribution of the latter, suggests that both types of mycorrhizal fungi compete for the same niche. The co-occurrence of ectomycorrhizas and arbuscular mycorrhizas might be explained by diffe rences between ECM and AM hosts and fungi in their colonizing abilitie s.