Biodegradation and regeneration of water-soluble carbon in a forest soil: leaching column study

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.

Keywords Dissolved organic carbon • Water-extractable carbon • Biodegradation • Ammonium • Nitrate • Leaching • Below-ground carbon dynamics