PHOSPHORUS-NUTRITION OF ECTOMYCORRHIZAL AND ARBUSCULAR MYCORRHIZAL TREE SEEDLINGS FROM A LOWLAND TROPICAL RAIN-FOREST IN KORUP NATIONAL-PARK, CAMEROON

The relationship between mycorrhizal colonisation and phosphorus acqui red by seedlings of the arbuscular mycorrhizal tree Oubanguia alata Ba k f. (Scytopetalaceae) and the ectomycorrhizal tree Tetraberlinia more liana Aubr. (Caesalpinioideae) was evaluated at low and high inorganic phosphorus availability. AM colonisation was positively correlated wi th phosphor us uptake by O. alata at low, but not at high phosphorus a vailability. Seedlings growth was positively related to arbuscular myc orrhizal colonisation at both low and high phosphorus availability, su ggesting that growth promotion by arbuscular mycorrhizas is not nr sim ply related to an increase of phosphorus uptake. In contrast, phosphor us uptake by T. moreliana was correlated with EM colonisation at both low and high phosphorus availability, but there was no relationship be tween growth and ectomycorrhizal colonisation. Promotion of phosphorus uptake by arbuscular mycorrhizas and ectomycorrhizas at low phosphoru s availability is consistent with the cooccurrence of the two types of mycorrhiza in tropical rain forests where available soil phosphorus i s low. However, ectomycorrhizal colonisation may also be of advantage where inputs of phosphorus rich litter raise the phosphorus status of the soil, as seen in the groves of ectomycorrhizal trees in Korup Nati onal Park, and may be one of the factors reinforcing local dominance b y these trees.