Content and stability of topsoil and deep soil organic carbon under different vegetation types in the Bieszczady Mountains (Eastern Carpathians, SE Poland)

Mountain soils are important carbon reservoirs, yet the distribution and stability of soil organic carbon (SOC) in deep soil horizons remain poorly understood, particularly in temperate mid-elevation mountain regions. Although vegetation is recognized as a key control on the vertical distribution and stabilization of SOC, its influence on deep soil carbon pools remains largely unexplored. This study investigates the content, composition and stability of SOC in topsoil and deep soil horizons under different vegetation types in the Bieszczady Mountains (Eastern Carpathians, SE Poland).

The research was conducted under four contrasting vegetation types representing forest and non-forest ecosystems: Vaccinietum myrtilli, Calamagrostietum arundinaceae, Dentario glandulosae–Fagetum and Campanulo serratae-Agrostietum. For each vegetation type, representative soil profiles were excavated and sampled by genetic horizons from surface organic layers to deep mineral horizons. Basic soil properties, including pH, soil texture and mineral composition, were determined to characterize environmental controls on SOC stabilization.

Soil organic carbon and total nitrogen contents were measured using elemental analysis. The chemical composition of soil organic matter (SOM) was examined using Fourier-transform infrared (FTIR). To evaluate SOC stability, soil organic matter (SOM) was separated using a density-based physical fractionation method, which allows the isolation of labile particulate organic matter from mineral-associated, more stable carbon pools. Additionally, soil respiration measurements were used to assess microbial activity and potential SOC mineralization.

This approach helps to understand how different types of vegetation influence both the quantity and stability of SOC in topsoil and subsoil layers. The results can provide new insights into carbon sequestration mechanisms in temperate mountain ecosystems and hightlight the significant role of deep soil horizons in long-term carbon storage.