Biochemical Stability of Water-Soluble Organic Matter in Tundra Soils of the Khibiny Mountains during Postfire Succession

Abstract

The dynamics of the content of water-soluble organic matter (WSOM) and its resistance to microbiological transformation in the Entic Folic Podzol of the postfire succession in the dwarf-shrub mountain tundra of the Khibiny Mountains are studied. A medium-intensity fire does not cause a statistically significant decrease in the soil WSOM content as compared to the reference plot. The activity of WSOM mineralization is mainly determined by the WSOM properties rather than by the microbial community. The dynamics of biodegradation is adequately described by a two-component first-order exponential model with a statistically significant existence of fast-mineralized (mean residence time, <1 day) and slow-mineralized (mean residence time, 33 to 111 days) pools. The maximum share of the fast pool is typical of the soil immediately after a fire and smoothly decreases during further postfire succession. During biodegradation, a biokinetic selection of the aromatic hydrophobic compounds most resistant to microorganisms is observed, while the simple nitrogen-containing components of WSOM are the first to be consumed by microorganisms.