Fine root dynamics in a Bornean rain forest

Abstract

The role of fine root dynamics in the carbon and nutrient cycles of a primary, lowland dipterocarp rain forest in Sabah, Malaysia was investigated. A new method for estimating fine root production was developed which involved the combination of excavation and rhizotron techniques to separately quantify spatial and temporal variability in the root system. The aim was to produce a method that could quantify the simultaneous occurrence of fine root production, mortality and decomposition. The biomass of roots ^2, >2-<5, >5-^10, >10-^15 mm diameter in the top 1.2 m of the soil was 2830, 3544, 2310, 2157 kg ha ' respectively. Fine root (<2 mm diameter) production and disappearance were estimated as 4018 and 4843 kg ha' yr'. The concentration of acetic acid extractable phosphorus in the soil was very low (0.7 mg kg ' in the top 5 cm) and the C:N ratio high (21). The hypothesis that soil fertility, and in particular phosphorus availability, is the primary factor governing fine root biomass in lowland tropical rain forests was discussed. Fine root production and disappearance rates were expressed in terms of a nutrient flux into and out of fine root biomass. No evidence was found to support the hypotheses that nutrients were retranslocated out of fine roots during senescence or that nitrogen, phosphorus or potassium were potentially limiting to fine root growth. It was suggested that greater synchrony was recorded in rates of fine root growth than has previously been recorded in rates of above-ground litterfall. Fine roots were found to be less important than above-ground litterfall in supplying the soil with organic matter. A new method for quantifying the decomposition rate of fine roots involving the disappearance rate of fine roots on rhizotrons was developed. Fine root decay rates were found to be similar to previously reported rates of leaf decay in the same forest. Fine roots were decomposing on average for 70% of their Persistence.