High dissolved organic carbon deposition is buffered by surface soil in a headwater catchment of a subtropical plantation

Abstract

High atmospheric dry and wet deposition of dissolved organic carbon (DOC) may contribute to net ecosystem carbon balance (NECB), but the input and output fluxes of DOC and their transport processes in a catchment remain unclear. Here, to elucidate the importance of DOC in NECB from the view of Earth’s critical zone, we measured the water fluxes of inputs (precipitation, throughfall, and stemflow) and outputs (soil leachate, surface flow, interflow, streamflow and groundwater) and their DOC concentrations in a subtropical plantation headwater catchment. Our results showed that dry DOC deposition from plant-derived dust and exudates (22,317 kg C km−2 yr−1) was about 4.5 times higher than the wet DOC deposition from precipitation (4966 kg C km−2 yr−1), and accounted for 3.88 and 0.86% of the net ecosystem C productivity (NEP) (5.75×105 kg C km−2 yr−1), respectively. In comparison, DOC fluxes in stream and groundwater were 5912 and 3905 kg C km−2 yr−1, indicating that soil-buffered DOC flux was 17,466 kg C km−2 yr−1 and accounted for 3.04% of NEP. A positive correlation between DOC and pH and total dissolved solids in soil leachate indicated that the biophysical and chemical absorption bridged the interaction between soil minerals and organic carbon. Our results underline the importance of including plant-derived DOC deposition in carbon sink estimations in subtropical plantation headwater catchments.