Dissolved black carbon in throughfall and stemflow in a fire-managed longleaf pine woodland

Abstract

The interception of rainfall by trees enriches rainwater with tree-derived dissolved organic matter (tree-DOM), which represents the first terrigenous source of DOM during storm events. The tree-DOM is then exported from the canopy via rainfall that drips from leaves and branches (throughfall) or is funneled down the tree trunk (stemflow) to the forest floor. Here, we evaluate contributions of dissolved black carbon (DBC) to tree-DOM in fire-managed longleaf pine woodlands (Pinus palustris). These are the first quantitative measurements of throughfall and stemflow DBC for any type of forest or tree species. The inter-storm variability of tree-DOM concentrations, composition, and optical properties in throughfall and stemflow were also examined. Tree-DOM was enriched in dissolved organic carbon (DOC) and DBC compared to rainfall, and concentrations did not vary with storm size. Therefore, longleaf and slash pines contain a large repository of leachable organic matter that was not significantly diminished, even during large storm events. The aromaticity of stemflow DOM increased with amount of rainfall, suggesting bark may need to undergo a certain degree of saturation for the solubilization of DBC and other aromatic components. In tree-DOM, DBC comprised ~ 2% of DOC. A simple mass balance suggested annual yields of DBC in throughfall and stemflow (50–350 kg-DBC and 19 kg-DBC km−2 year−1, respectively). Therefore, atmospheric deposition would be enough to sustain a continual source of tree-derived DBC in longleaf pine ecosystems regularly maintained by fire.