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Understanding the mechanisms involved in the building up of organic matter pools with long residence time in soils is fundamental for the comprehension of carbon dynamics. As organic matter persistence depends on environmental conditions and soil properties, both pedogenic processes and factors should be key elements for identifying the link between organic pools and stabilization mechanisms.In the Ligurian Alps, an area where pedodiversity is large, we evaluated the importance of two soil formation factors, vegetation and parent material, and consequently pedogenic processes and soil features, on organic matter stabilization in forest soils. We thus selected 20 profiles, developed on different parent materials and forest stands, which ranged from Regosols, to Cambisols, to Chernozems/Kastonozems, to Podzols and Luvisols/Alisols. In the mineral horizons, we determined the soil physico-chemical properties and fractionated organic matter into labile and stabilized (recalcitrant and mineral-bound) pools using NaClO followed by HF treatment.Soil and organic matter characteristics were primarily explained by the parent material and soil type, while vegetation affected organic matter quality but not the total amounts. The labile and recalcitrant organic pool proportions were linked to parent material likely through its effect on pH and other microenvironment characteristics. The mineral-associated organic matter instead followed a pedogenic pathway, with higher percentages of stable organic carbon in illuvial B horizons from Podzols and Luvisols/Alisols. In the study area, therefore, the most developed soils were relatively more resilient for organic matter conservation than less developed soils, which are more prone to C losses.

Because of extensive Pleistocenic glaciations, which erased most of the previously existing soils, slope steepness and climatic conditions favoring soil erosion, most soils observed in the Alps (and in other mid-latitude mountain ranges) have developed during the Holocene or Late Glacial period.However, in few sites, particularly in the outermost sections of the Alpine range, Pleistocene glaciers covered only small and scattered surfaces, and ancient soils could be preserved for long periods on stable surfaces. In many cases, these soils retain good memories of Quaternary periglacial activity, which have never been characterized on the Alpine range. Based on both geomorphological and pedological interpretations, this work aims to investigate these environments, providing, therefore, new evidences to support paleoclimate reconstructions on the Alps.We described and sampled soils on stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern Piemonte, Italy). The sampling sites were between 600 to 1600 m a.s.l., under present day lower montane Ostrya carpinifolia, montane Fagus sylvatica forests or montane heath/grazed grassland, on quartz-rich substrata.The surface morphology often showed strongly developed fossil periglacial morphologies such as large-scale patterned ground, blockfields/blockstreams or solifluction sheets.The soils preserved in such Quaternary periglacial landforms normally showed stratification of different layers (units), separated by structural discontinuities, evidencing different depositional settings and different pedogenic development degree. A strong cryogenic granulometric sorting characterized all the observed soils/paleosols, with silt-enriched horizons and lateral differentiation of sand-and stone-rich parts and fine enriched ones; organic matter was irregularly distributed at depth as a result of past cryoturbation. Compact and dense layers with strong platy/lenticular structural aggregation, wedge casts and large-scale cryoturbations were described below fixed depths in all soil profiles. Thus, surface morphology and soil properties suggest the presence of permafrost during cold Pleistocene phases, with two main active layer thicknesses at 60-120 and 100-160 cm depths respectively.

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