Ectomycorrhizal rain-forest legumes and soil phosphorus in Korup National Park, Cameroon


  • Permission to conduct this research was given by the Ministry of Higher Education and Scientific Research in the Cameroon. We are grateful to the Leverhulme Trust (D.M.N., during the tenure of a Research Fellowship) and Carnegie Trust (I.J.A.) for financial support. S. J. Gardiner undertook the chemical analyses of the 1984 and 1986 samples at Stirling, and F. Namata helped invaluably in the field. We are grateful also for the assistance afforded us by British Embassy and the British Council in Yaoundé, and Plantations Pamol du Cameroun Limited. Full acknowledgements for the original enumeration study and soil sampling are given in Gartlan et at. (1986).


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.