Self-restoration of post-agrogenic Albeluvisols: Soil development, carbon stocks and dynamics of carbon pools

- Study focuses on the self-restoration of post-agrogenic Albeluvisols.
- Vegetation and soils developed towards their natural composition.
- No full restoration took place within the time of 68 years.
- Carbon stocks did not change, but show a distinct redistribution within soil layers.
- Soil organic carbon sequestration occurred dominantly as free particulate organic matter.

This chronosequential study focuses on the vegetation succession, pedogenesis, carbon stocks and functionally different carbon pools of post-agrogenic Albeluvisols under self-restoration in the Taiga zone of the European part of Russia. The sites investigated were comparable in terms of climate, soil texture and land-use history, but differed in duration of agricultural abandonment, covering 4, 12, 17 and 68 years of self-restoration. During self-restoration, the vegetation showed a development towards a mesophytic spruce forest. Pedogenesis resulted in recovery of morphological and chemical features with a vertical differentiation typical for the undisturbed Albeluvisols. During self-restoration, new organic surface layer (O) and new humic topsoil horizon (Ah) were developed. At the end of the chronosequence, the bottom of the well visible former ploughing horizon showed eluvial characteristics. Simultaneously, leaching caused a pH decrease of about 1.8 units, loss of the exchangeable cations, depletion of base saturation from 100% to 18%, and loss of nutrients. A vertical differentiation due to redistribution processes was found for soil organic carbon (SOC) and plant available phosphor and potassium. During self-restoration, the measured carbon stocks did not change substantially in the upper 0.5 m, but show a distinct redistribution within different soil layers, causing SOC accumulation from 0.64 to 0.78 kg m− 2 in the organic surface layers and from 0.75 to 2.64 kg m− 2 in 0-0.1 m, but SOC loss from 3.60 to 1.71 kg m− 2 in 0.1-0.5 m. The simulation results showed also minor alterations for the chronosequence time interval, followed by an increasing SOC sink functioning at long terms of up to 200 years. The investigation of functionally different SOC fractions showed a significant enrichment of free particulate organic matter (POM) and occluded POM, hot water extractable carbon (Chwe), and carbon in grain size fractions, significantly following the increase of total SOC during self-restoration. Nevertheless, self-restoration affected the distribution pattern of carbon to functionally different pools, predominantly stimulating SOC sequestration within free POM fraction. Despite all these alterations the study showed no full restoration for the vegetation and the soils within the chronosequential time scale of 68 years.