Organic matter dynamics in relation to two forest types in Korup National Park, SW Cameroon
This study presents new data on soil organic matter dynamics in relation to two forest types in a strongly seasonal lowland rainforest in Korup National Park, SW Cameroon. Organic matter dynamics at the start of the wet season were investigated by quantifying changes in the amount of the standing crop of surface organic matter and light fraction soil organic matter (LF.SOM) in five replicate plots with low (≤ 15%) basal area ectomycorrhizal trees ≥ 30 cm gbh (LEM forest type), and five with high (≥ 45 %) basal area ectomycorrhizal trees (HEM forest types). Soil samples were collected in the wet season from three soil depths: an organic-enriched layer (0 - 3 cm), 3 - 8 cm and >8 cm layers, in both HEM and LEM forest types, in 1993 (3 harvests), and in 1994 (8 harvests). LF.SOM and heavy fraction soil organic matter (HF.SOM) were separated from < 2 mm whole soil using tap water and/or saturated NaI solution (density 1.65 g cm-3). Other pools of organic matter quantified included that in the > 2 mm soil fraction and in the < 2 mm sieved whole soil. LF.SOM accounted for 10 - 40 % soil organic matter, 7 - 34 % carbon, 2 - 28 % N and 2 - 25% P of the < 2 mm whole soil across forest types and down the soil profile. The > 2 mm soil fraction accounted for 14 - 21% carbon, 11 - 20 % N, and 6 - 22% P of total soil (i.e. <2 mm whole soil + > 2 mm soil fraction). The amount of LF.SOM was not significantly different between the two forest types at all depths. Both the amount of the standing crop of surface organic matter and LF.SOM declined as the wet season progressed. However, the amount of LF.SOM declined faster (55 %) in the LEM forest than in the HEM forest (22 %). On the other hand, the amount of HF.SOM increased over the same period. A vertical gradient in LF.SOM content was observed.