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Effective retention of litter-derived dissolved organic carbon in organic layers
- Müller, Matthias, Alewell, Christine, Hagedorn, Frank
- Soil biology & biochemistry 2009 v.41 no.6 pp. 1066-1074
- plant litter, dissolved organic carbon, soil organic matter, organic horizons, treeline, carbon dioxide, stable isotopes, carbon, soil respiration, microbial activity, soil microorganisms, root exudates, leaching, biodegradability, Switzerland
- This study aimed to gain insight into the generation and fate of dissolved organic carbon (DOC) in organic layers. In a Free Air CO2 Enrichment Experiment at the alpine treeline, we estimated the contribution of 13C-depleted recent plant C to DOC of mor-type organic layers. In an additional laboratory soil column study with 40 leaching cycles, we traced the fate of 13C-labelled litter-DOC (22 and 45 mg l-1) in intact Oa horizons at 2 and 15 °C. Results of the field study showed that DOC in the Oa horizon at 5 cm depth contained only 20 ± 3% of less than six-year-old C, indicating minor contributions of throughfall, root exudates, and fresh litter to leached DOC. In the soil column experiment, there was a sustained DOC leaching from native soil organic matter. Less than 10% of totally added litter-DOC was leached despite a rapid breakthrough of a bromide tracer (50 ± 7% within two days). Biodegradation contributed only partly to the DOC removal with 18-30% of added litter-DOC being mineralized in the Oa horizons at 2 and 15 °C, respectively. This was substantially less than the potential 70%-biodegradability of the litter-DOC itself, which indicates a stabilization of litter-DOC in the Oa horizon. In summary, our results give evidence on an apparent 'exchange' of DOC in thick organic layers with litter-DOC being retained and 'replaced' by 'older' DOC leached from the large pool of indigenous soil organic matter.