Fluxes of dissolved organic carbon in three tropical secondary forests developed on serpentine and mudstone

Leaching of dissolved organic carbon (DOC) from the organic (O) horizon plays an important role in soil C cycles and formation of soil organic matter. The magnitude of DOC fluxes in throughfall and soil solutions was quantified in three tropical secondary forests affected by the former selective logging in East Kalimantan, Indonesia. The sites were located on the Oxisol soil formed on serpentine and two Ultisol soils formed on mudstone. The DOC fluxes in the soil profiles are highest in the O horizons, decreasing markedly with depth at all sites. The DOC fluxes from the O horizons varied greatly from 166 to 261 kg C ha− 1 yr− 1 in Ultisols to 603 kg C ha− 1 yr− 1 in Oxisol, which corresponded to 3.7 to 11.4% of C input. The DOC export from the B horizons was consistently low (10 to 31 kg C ha− 1 yr− 1) due probably to the high DOC adsorption of the clayey Oxisol and Ultisol soils. The contribution of DOC fluxes to soil C balance is minor compared to litterfall (4.0 to 4.8 Mg C ha− 1 yr− 1) and organic matter decomposition (4.2 to 4.7 Mg C ha− 1 yr− 1), however, DOC leached from the O horizon appears to be an important C source into the mineral soils. The magnitude of DOC leaching from the O horizon increased with decreasing P concentration in foliar litter, whereas DOC consumption in the deeper soil horizons is related to clay content that originates from parent materials. The roles of DOC leaching to soil C cycle are shown to be variable at a local scale, depending on vegetation and parent material.

Research highlights
► The DOC fluxes in throughfall and soil solution were quantified under tropical forests in East Kalimantan, Indonesia.
► The contribution of DOC export to soil C balance was minor due to high DOC adsorption in the clayey Oxisol and Ultisol soils.
► The DOC fluxes from the O horizons varied greatly from 166 kg Cha−1yr−1 in the Ultisol soils to 603 kg Cha−1yr−1 in Oxisol soil.
► The importance of DOC fluxes to C source to the mineral soils varied from soil to soil at a local scale.