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Abstract:
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.
