Phosphorus Dynamics in a Lowland African Rain Forest: The Influence of Ectomycorrhizal Trees

• Published in: Ecological monographs 1997-08, Vol.67 (3), p.367-409
• Main Authors: D. Mc C. Newbery, Alexander, I. J., Rother, J. A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Beans; Biological and medical sciences; Ecology; Environmental aspects; Forest ecology; Forest litter; Forest soils; Fundamental and applied biological sciences. Psychology; Habitat (Ecology); Hems; Legumes; Mimosaceae; Minerals; Nitrogen; Organic soils; Phosphorus; Plant canopies; Rainforests; Soil ecology; Synecology; Terrestrial ecosystems; Trees
• ISSN: 0012-9615; 1557-7015
• DOI: 10.2307/2963460

In the southern part of Korup National Park, Cameroon, nine replicate plots (40 × 80 m) in forest with low abundances (5-15% of the basal area of all trees ≥ 30 cm gbh [girth at breast height]; LEM) and nine with high abundances (45-68%; HEM) of ectomycorrhizal caesalpiniaceous legumes were selected from an earlier enumeration along an east-west 5-km transect. The codominant caesalps in HEM plots were Microberlinia bisulcata, Tetraberlinia bifoliolata, and T. moreliana, and ordination showed the LEM and HEM plots to be floristically distinct. The HEM plots lay in a large well-defined patch of these caesalps, set within surrounding LEM forest. A further contrast to HEM forest was achieved by selecting six LEM and six VLEM plots (very low, ≈ 0% ectomycorrhizal trees) on a second transect 12 km to the north. Korup has an annual rainfall of 5180 mm with one very distinct 3-mo dry season (December-February). The soils are sandy, acidic, and very phosphorus poor. The aim was to determine whether LEM and HEM plots differed in their litter and soil phosphorus status and the characteristics of their phosphorus cycles. On 13 occasions between August 1988 and September 1990, litter and soils in the surface root layer and the mineral layer 5 cm below were sampled on the main transect and analyzed for phosphorus fractions. This analysis distinguished between inorganic and organic forms and provided various measures of liability. Nitrogen and carbon contents, pH, and moisture contents of each layer, depth of the root layer, and amounts of litter (i.e., litter mass) and soil were the other main variables. In a subset of plots, leaf litterfall was collected over the period and analyzed for phosphorus and nitrogen, and two litter-bag experiments in early wet seasons estimated rates of litter disappearance. Root biomass and change with depth were estimated from pit samples within the plots. HEM plots had slightly higher mean basal area of trees than LEM plots (32.3 and 27.1 m2/ha, respectively) and higher fine root (≤ 5 mm diameter) biomasses (519 and 364 g/m2, 0-5 cm), but the same mean litter mass (155 g/m2) and annual leaf litterfall (720 g/m2) and very similar disappearance rates (1.82 g·m-2·d-1on litterfall/mass basis; t1/2of 53 d from litter bags). Litter mass (and litterfall) reached a clear peak in the mid-dry season in both HEM and LEM plots (slightly earlier in HEM), almost completely disappearing by mid-wet season. The phosphorus concentrations in HEM falling lea