Biodegradation and regeneration of water-soluble carbon in a forest soil: leaching column study
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We hypothesized that water-soluble C is a major substrate for microbial activity and studied the susceptibility of water-soluble C both to leaching and to microbial degradation. Soil columns, consisting of A-horizon top soil with and without tree seedlings, were leached every 2 weeks for 20 weeks. Water-soluble material was extracted from the soils before and after the 20-week study. Biodegradability of dissolved organic C (DOC) was assessed by solution incubation. DOC in leachates was constant over the 20 weeks and the extractable C pool declined by 31–40% between the start and end of the experiment. The amount and biodegradability of both leachates and extracts were lower in the presence of seedlings. Water extracts contained 8–17 times more DOC than leachates. Percentage biodegradable DOC was 13–16% in leachates and 18–27% in extracts. A soil C destabilization model was proposed based on the measured pools (particulate, water-extractable, and leachable C) and estimates of soil respiration and microbial biomass from the same soil. Leaching loss accounted for 8–14% of the total C destabilized. Due to its low concentration and biodegradability, we concluded that leachable C was not a significant substrate for heterotrophic soil respiration in the studied system. The role of water-extractable C as a major substrate was less clear, as the regeneration rate of the extractable C in soil is still unknown.
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