Dissolved organic carbon from the forest floor with different decomposition rates in a rainforest in south-eastern Brazil

Abstract

Dissolved organic carbon (DOC) fluxes between environmental compartments are an important component of the global carbon balance and pedoecological processes. Tropical forests are the world’s most productive ecosystems and the forest floor is the main DOC-source in these environments. This study aimed to compare DOC concentrations under the forest floor with different litter-decomposition rates. Four study plots were established along a hillslope profile where heterogeneity was observed in previous studies: drainage divide (DRD); upper-hillslope (UHS); lower-hillslope (LHS); and valley bottom (VLB). Inversely proportional to the decomposition rates, the litter storage in this profile was as follows: DRD > UHS ≅ LHS > VLB. The bulk precipitation was a DOC source statistically similar to canopy-washing, and DOC concentrations in throughfall were statistically similar among the hillslope positions. There was some dilution effect in the inter-event modulation, mainly in throughfall and associated with the rainfall maximum intensity. The DOC concentrations under the forest floor were related in a non-linear manner with the litter storage: thin stocks in VLB showed lower DOC concentrations, but the thicker stocks in DRD did not materialise in the highest concentrations; the litter storage in UHS and LHS showed higher DOC-concentrations as a result of a balance between maintaining the DOC-source and making new soluble byproducts available that favoured the DOC-release to water.