Fluxes of dissolved organic carbon in two tropical forest ecosystems of East Kalimantan, Indonesia

Leaching of dissolved organic carbon (DOC) from the organic horizon is an important process involved in translocation and stabilization of organic matter in forest soils. Despite there being many studies on the DOC fluxes in temperate forest soils, very little information is available in tropical forest soils. The roles of DOC leaching in soil organic carbon cycle were evaluated by quantifying the fluxes of DOC in throughfall and soil solution in the Ultisols under tropical secondary and pristine forests in East Kalimantan, Indonesia. The fluxes of DOC in the soil profiles are highest from the O horizon (470-562 kg C ha− 1 yr− 1), decreasing markedly in the A and B1 horizons of the two Ultisols studied. DOC fluxes from the O horizon are comparable to those of temperate forests because of the greater amounts of precipitation, substantial C input (3.7-4.3 Mg C ha− 1 yr− 1) and its rapid decomposition (4.2-5.4 Mg C ha− 1 yr− 1). The proportion of DOC leaching to C input in the O horizon (12.7-13.2%) is similar to Spodosols under boreal and temperate forests. DOC leached from the O horizon appears to be an important carbon source into mineral soils, even in tropical regions. At the same time, DOC leaching contributed to eluviation of Al and Fe from the O horizon and their illuviation in the subsurface soil horizons. It was quantitatively shown that DOC leaching is important to the translocation of organic matter, Al and Fe in the acidic Ultisols in tropical forests, as well as the soils under boreal and temperate forests that undergo podzolization.