Effects of development stage on organic matter transformation in Podzols

Podzols are soils in which organic acid and mineral leaching results in the formation of a B horizon, which often contains a high amount of organic carbon. As Podzols cover large areas of the globe (±12% in European forests), carbon stocks of Podzols are important in the context of climate change mitigation. However, the dynamics of carbon storage in Podzols are not yet fully understood. In this study pyrolysis-GC/MS was used to investigate organic matter (OM) transformation from leaf litter to stabilized OM in the B horizon. It was analysed how OM transformation differed for different stages of Podzol development (leaf litter > incipient > active > buried) and for different vegetation types (deciduous, coniferous, mixed) in a temperate climate. The consequences for carbon storage in Podzols were evaluated. Identified pyrolysis products (1 0 5) were assigned to different chemical groups (lignin phenols, aliphatics, etc.) and relative abundances were calculated. The relative abundance of (lignin) phenols decreased from 42 to 58% in leaf litter and fermentation material to 34–49% in A and B horizons of incipient Podzols, to 14–47% in active Podzols, and to 10–18% in buried Podzols. At the same time, the relative abundance of aliphatics increased from 10 to 14% in leaf litter and fermentation material to 19–27% in the A and B horizons of incipient Podzols, to 13–56% in active Podzols, to 27–63% in buried Podzols. Vegetation type did not cause large changes in the OM composition. Incipient Podzols had a soil OM composition similar to the illuvial dissolved OM (DOM) input, as the buildup of stabilized OM has just started. Concluding, the soil OM composition changes for different Podzol development stages (incipient > active > buried), and stabilization of aliphatics increases when the relative input of illuvial DOM, and thus of lignin phenols, decreases.