Dissolved organic carbon from European beech logs: Patterns of input to and retention by surface soil

Abstract

The flux of dissolved organic carbon (DOC) from aboveground litter into the soil is generally considered an important pathway for carbon transport. However, the extent to which dead wood, a highly concentrated source of carbon (C), may contribute not only to this flux but also to the accumulation of soil organic carbon (SOC) is still unknown. Here, concentrations and fluxes of DOC in solution beneath 5 logs of Fagus sylvatica were quantified using tension lysimeters. Soil samples beneath and adjacent to an additional 18 logs were analyzed for SOC. Concentrations of stable C isotopes were determined in wood of logs, DOC, and SOC to follow the fate of C from logs to the soil. Mean DOC concentrations in soil solution beneath logs were highly variable and ranged between 11.6 ± 5.8 mgL−1 (± SD) and 696 ± 654 mg·L-1, while beneath litter without logs the DOC concentrations had an average value of 10 ± 3 mg·L-1. Peak DOC concentrations beneath logs reached 4317 mg·L-1. At 0–20 cm soil depth, SOC concentrations and SOC pools beneath logs were not higher than for control soils. The difference in the composition of stable C isotopes between wood (-25.5 ± 1.0%o) and litter (-28.4 ± 0.2%o) was maintained in DOC and SOC beneath respective substrates. A calculated amount of 20.5 ± 13.6% of the original SOC within 0–20 cm mineral soil was exchanged over a period of 17 ± 8 y by C from logs. However, despite the increased DOC fluxes, SOC pools beneath logs did not increase.