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Keywords:

  • Key words: Tropical rain-forest, ectomycorrhizas, phosphorus, Caesalpinioideae, ordination

SUMMARY

The mycorrhizal status of a group of caesalpinioid legumes in lowland rain-forest in Korup National Park, SW Cameroon, was examined. Species in ten genera, Anthonotha, Aphanocalyx, Berlinia, Didelotia, Gilbertiodendron, Julbernardia, Microberlinia, Monopetalanthus, Tetraberlinia(tribe Amherstieae) and Afzelia(tribe Detarieae) were ectomycorrhizal. These species were not uniformly distributed in the forest, and three large emergent species Microberlinia bisulcata A. Chev., Tetraberlinia bifoliolata(Harms) Hauman, and T. moreliana Aubr. in particular appear to form groves c. 600 m across. This type of distribution may be related to the ectomycorrhizal habit.

A previous large scale enumeration and soil survey on four 5 km transects of plots in the forest, carried out during the wet season, had revealed an association between these ectomycorrhizal legumes and low concentrations (leqslant R: less-than-or-eq, slant 5 μg g-1) of extractable phosphorus in the mineral soil. In the current study part of one of the original transects in a low phosphorus area of the forest, where ectomycorrhizal trees comprise 29 % of the basal area, was resampled at the subplot level during the dry season. Whereas in the wet season soil phosphorus had been lower (2·8 μg g-1) within the ectomycorrhizal groves than without (3·8 μg g-1), in the dry season the situation was reversed and the overall concentrations were higher (12·3 and 7·9 μg g-1 respectively). Ordination analysis re-affirmed the association of the three Microberlina/Tetraberlinia species with relatively low concentrations of extractable phosphorus in the wet season but relatively high ones in the dry season. The groves are characterized by high inputs of leaf litter in the dry season, extensive colonization of surface organic matter by ectomycorrhizas and hyphal strands, and high carbon: extractable inorganic phosphorus ratios in the mineral soil in the wet season. These features are discussed in relation to the presumed ability of ectomycorrhizas to utilize organic phosphorus.