• Ectomycorrhizas;
  • arbuscular mycorrhizas;
  • distribution;
  • tropical rain forest;
  • co-occurrence

The frequent co-occurrence of ectomycorrhizas and arbuscular mycorrhizas in the same ecosystem raises the question about how two functionally different mycorrhizal associations exploit a spatially heterogeneous habitat. Horizontal (in plots along a transect of 3750 m crossing forest types of low and high abundance of ectomycorrhizal (ECM) host species) and vertical (across profiles of litter and 0–5 cm, 10–15 cm, 25–35 cm soil layers) distribution of ectomycorrhizas and arbuscular mycorrhizas 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 two types of mycorrhiza exploit different niches. No pattern was observed in either ECM or arbuscular mycorrhizal (AM) fractional colonization with depth in the profile even though most of the variation in soil parameters was vertical. Only local (between monoliths within plots) horizontal differences were found in soil parameters. By contrast, horizontal differences in fractional colonization were found between forest types, and between monoliths, for ectomycorrhizas but only between monoliths for arbuscular mycorrhizas. The lack of a clear relationship between both horizontal and vertical distribution of ECM and AM fractional colonization and soil parameters suggests that both fungal groups are equally able to colonize the same niche, at the scale of our experiment. 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 distribution of arbuscular mycorrhizas in forest areas dominated by ectomycorrhizas 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 differences between ECM and AM hosts and fungi in their colonizing abilities.