Quantity and quality of dissolved organic carbon released from coarse woody debris of different tree species in the early phase of decomposition

The release of dissolved organic carbon (DOC) from decomposing coarse woody debris (CWD) may result in large DOC inputs to the forest soil. Here we investigated the influence of tree species on the amounts and quality of DOC from CWD in the early phase of decomposition. Logs from 13 tree species were exposed in winter 2008/2009 on the soil in a temperate Fagus sylvatica L. forest in Germany. Runoff solutions were periodically collected for 17 months from June 2011–November 2012 underneath logs and the net release of DOC was calculated for each log on an annual scale. The quality of DOC was assessed by its contents of soluble phenols, hydrolysable carbohydrates and by spectroscopic properties. Prior to field exposure of CWD, bark and sapwood were analyzed for their initial element content and water extractable DOC. Concentrations of DOC in log runoff were much (3–10 times) higher than in throughfall for all tree species. Average concentrations in runoff were largest under Quercus and Prunus and lowest under Tilia and Fraxinus. Accordingly, the net release of DOC from the logs was largest under Quercus and Prunus amounting to 60 and 56 g C m2 projected log area yr1, respectively. The DOC net release for the tree species was positively related to the initial phenol content of sapwood, but not to C/N ratios in bark and sapwood. On a monthly to annual scale, the amount of precipitation had only a small influence on the net release of DOC, but the DOC net release was larger in the growing than in the dormant season. The concentrations of hydrolysable carbohydrates in log runoff were largest for Prunus and Quercus and lowest for Fraxinus and Tilia. Average concentrations of total phenols in runoff ranged from about 2 to 7 mg L1 with Quercus, Fraxinus, Betula, Picea and Larix representing the upper range. Spectroscopic properties indicate that the DOC leached from logs is microbially modified and oxidized in comparison to DOC in initial bark and wood extracts. Our results suggest that the DOC release from CWD is tree species specific in terms of quantity and quality and causes huge DOC fluxes to the soil underneath CWD