Soil climate regulation services: high SOC stock in Podzols and Umbrisols in an alpine grassland (Valle Adamé, Italy)

The United Nations Sustainable Development Goals include soil conservation as an urgent climate action to be taken; alpine grassland soils, rich in organic matter and particularly vulnerable to climate change, require special attention. In the upper Adamé valley (Italy), the effects of soil and vegetation types and environmental parameters, on soil carbon (SOC) stock and other soil properties were evaluated. Sampling points were chosen starting from the main vegetation types (dominant species: Rhododendron ferrugineum, Nardus stricta, Festuca luedii, Adenostyles leucophylla and Salix herbacea). For each vegetation type, five plots were selected, within which three soil minipits were described and sampled by layers (0–10 cm, 10–20 cm and 20–40 cm), at 75 georeferenced points. The results highlighted that: (1) Podzols and Umbrisols showed high capacity to store OC in the top 40 cm (17.3 ± 8.2 kg m−2), whereas Fluvisols and Leptosols demonstrated a low capacity (5.0 ± 3.5 kg m−2); (2) topographical factors indirectly affected the variability of the SOC stock by influencing the spatial distribution of vegetation; (3) 74% of the SOC stock was sequestered in the upper 0–20 cm layer; (4) regardless of soil type, Festuca and Salix were the vegetation types that mostly contributed to the surface SOC enrichment, followed by Rhododendron, Nardus and Adenostyles. Following climate change, a shift of the Salix and Nardus vegetation types in favour of the Rhododendron type is expected in the short to medium term. As a consequence, a possible reduction in the effectiveness of the climate regulation service provided by the soils may occur.