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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 and 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.

Sorption of organic matter (OM) onto soil minerals affects OM dynamics, and is strongly controlled by mineral surface properties. Moreover, the degree and mechanism of interaction between different minerals may influence their surface reactivity. We therefore aimed to understand mineral surface modifications brought about by different Fe (hydr)oxide–vermiculite associations, and their influence on OM sorption. This could have important implications on OM dynamics in young hydromorphic soils where seasonal variations in redox conditions may affect mineral surfaces. Paddy soil-derived dissolved OM was used in sorption isotherms on mixed mineral phases obtained by precipitating different amounts of Fe (hydr)oxides on vermiculite. Results evidenced that the surface properties of vermiculite strongly drove Fe (hydr)oxide precipitation, and consequently OM sorption mechanisms. The change in surface charge with increasing Fe loading resulted in a higher retention of dissolved organic carbon. However, dissolved organic nitrogen adsorption isotherms and FTIR carboxyl vibrational shifts revealed the occurrence of two binding mechanisms, one driven by electrostatic attraction of N-containing compounds by the negatively charged vermiculite surface, and another involving ligand exchange of carboxylic compounds with the positive oxides, precipitated in localized nucleation sites. Moreover, the modification of both solution and solid properties during sorption, promoted the selective adsorption of aromatic molecules with increasing Fe coverage.

Soil erosion depends mainly on its intrinsic vulnerability (soil erodibility), which is represented by the K factor of the RUSLE equation. Soil erodibility is strictly related to soil structure, which depends mostly on soil particle-size distribution and organic and inorganic binding agents. Soil erodibility can be estimated through soil aggregate stability measurements. However, the effects of different humus forms on soil erodibility and aggregate stability are poorly understood. In this study, we evaluate the influence of different humus forms on these parameters, and consequently on soil susceptibility to erosion. In the Western Italian Alps, 67 sites were selected on different substrata under common forest vegetation types. In all sites, soil profiles and humus forms were described and classified. Soil samples from the upper mineral horizons (A or E) were analysed (SOM content, water aggregate stability that measures aggregates loss) and soil erodibility K factor was calculated. The results showed that surface mineral horizons in soils with Mor humus were the most susceptible to erosion because they had the greatest values of K and aggregates loss, and their surface mineral horizons were characterized by the lowest SOM content. Conversely, surface mineral horizons in soils with Amphi, which had the greatest SOM content, were the least susceptible to erosion, as demonstrated by the lowest K values and limited aggregates loss. Mull and Moder forms showed intermediate behaviours. Despite a similar SOM content as Mulls, Moders showed a slightly greater aggregates loss. At low SOM content, the aggregates loss increased but it varied significantly among the humus forms. In Moders, SOM variations induced large changes in aggregates losses while Amphi forms were the least influenced by SOM. These results show that the intrinsic characteristics of humus forms, derived from the biological factors to which they are associated, influence soil erodibility and aggregate stability and consequently soil susceptibility to water erosion.

In the Ligurian Alps, a wide range of site conditions that influence soil development and may affect humus variability is present. In this work, we wanted to evaluate the potentialities of humus forms as a synthetic indicator of both chemical properties of the humic episola and site conditions in the upper Tanaro Valley (NW Italy). Vegetation affected the C/N ratio of the least transformed organic horizons, but the effect disappeared in mineral ones, where soil pH was related to the parent material. All terrestrial humus forms were found in the area and their distribution well reflected the interactions between vegetation, lithology, elevation that shaped soil properties and affected the degradability of litter and its actual degradation by microorganisms and soil fauna. Humus forms were thus able to capture the ecological conditions, integrating the information provided by soil classifications.

Background and Aim: Biotic and abiotic factors contribute in shaping the distribution through the soil profile of elements released by mineral weathering; among them, leaching and biocycling dominate in temperate environments. We evaluated if the intensity of leaching and biocycling of nutrients can be modulated by element deficiencies linked to the abundance of serpentine in the soil parent material, i.e. if the most deficient elements are more efficiently retained. Methods: We selected twelve poorly developed soils from Northern Italian beech stands, with variable amounts of serpentinites in the parent material, and determined total and exchangeable Ca, Mg and K, as well as an index of abundance of serpentine minerals. Results: The total element content depended on the abundance of serpentines, while only exchangeable Mg was related to the parent material. The vertical trend of Ca and K indicated the role of biocycling in all soils, but the relative availability of Ca (ratio between exchangeable and total content) was much higher in the top horizons of serpentine-rich soils. Conclusions: The different element availability among soils suggested that the vertical distribution of available elements was linked to the parent material and that losses were limited in serpentine-rich soils, probably because plants take up the deficient elements as soon as they are released from litter and thus limit their leaching in deeper soil horizons.

The soil liquid (LL) and plastic limit (PL), and their difference PI (plasticity index) are physical properties related with the soil mechanical behavior, determined on the

In Podzols, organic matter (OM) is stabilized mainly by interaction with minerals, as a direct consequence of pedogenic processes. Metal-organic associations strongly affect OM surface features, particularly microporosity. Cemented ortstein horizons (CM) may form during podzolization, accompanied by a spatial arrangement of OM on mineral surfaces, which differs from that in non-cemented horizons (N-CM). To investigate the metal-organic associations and their changes during pedogenesis, we selected both N-CM and CM podzolic horizons, isolated NaClO-resistant OM and compared the specific surface area (SSA) before and after OM oxidation. The SSA was assessed by using N-2, to detect the pores in the range of micropores (< 2 nm) and mesopores (2-50 nm), and CO2, to measure a smaller microporosity (< 0.5 nm), which is not accessible to N-2. Only the N-CM samples showed the typical increase in N-2-SSA after the removal of labile OM, while a decrease was found in all CM horizons. The CO2-SSA revealed a large number of small micropores characterizing OM, both before and after oxidation. The smallest micropore classes (< 0.5 nm) were, however, more abundant in NaClO-resistant OM, which had therefore a larger number of N-2-inaccessible surfaces than the labile pool. The N-2-SSA data thus indicated a more homogeneous coverage of mineral surfaces by stabilized OM in CM samples. Because of the abundance of small micropores, OM in these podzolic B horizons had extremely large CO2-SSA values (about 800 m(2) g(-1)), with sharp differences between the NaClO-labile OM (290-380 m(2) g(-1)) and the NaClO-stabilized pool (1380-1860 m(2) g(-1)), thus indicating very reactive illuvial organic materials.

Soils on the Alps are usually weakly developed, both because of the extensive Pleistocene glaciations, and because of slope steepness and climate enhancing erosion. However, on some stable, relict surfaces, particularly in the outermost sections of the Alpine range, some highly developed soils are apparently in contrast with Holocene soil forming conditions. In this work we assess the extent of pedogenesis in some of these soils, located under montane-level vegetation in the Ligurian Alps (SW Piemonte, Italy), and relate it to the effects of climate and parent material. The considered well developed profiles showed signs of extremely different pedogenetic processes on the different lithotypes. In particular, Podzols with extremely thick E horizons (up to more than 2 m thick) and very hard, thick ortstein or placic horizons were formed on quartzite. Reddish “terra rossa” Luvisols were formed on limestone. Red, extremely acidic Alisols were formed on shales. The chemical properties, the micromorphology and the clay mineralogy demonstrated high intensity pedogenic trends, and were characteristic of processes usually occurring under different climates. They may therefore represent excellent pedo-signatures of different specific past climatic/environmental conditions, as a response of different lithologies to specific soil-forming environments, which range from warm and humid climates typical of red Alisols and Luvisols, to cool and humid/wet climates leading to the formation of Podzols with ortstein/placic horizons.

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 in 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/Kastanozems, 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.

In podzolic B horizons illuviated Al, Fe and organic matter (OM) increase with the ongoing of the pedogenic process. Depending on OM load on mineral surfaces, modifications of the soil surface properties are expected and may influence OM stabilisation. The proportion of labile organic pools should thus vary depending on the type of podzolic horizon. In this work, we selected B horizons at increasing intensity of podzolisation, evaluated the labile OM pools through oxidation with 2 % NaClO and characterised surface properties with N2 and phosphate sorption. Before and after oxidation, we assessed the NaOH-extractable OM fractions. Oxidation was more effective on the least polar organic compounds and led to an increase in the fulvic to humic acid ratio. Specific surface area (SSA) increased after oxidation only in the least podzolised horizons, while selectively preserved OM induced a decrease in SSA in the more developed Bs, Bsm and Bhs. Phosphate sorption induced a release of OM and always decreased after oxidation, although variations in P affinity for the surfaces were observed. The effect of oxidation on surface parameters pointed to a specific association between organics and minerals that changed during soil development. At the very beginning of podzolisation, the dominant forms seemed related to organo-metallic complexes with little interaction with surfaces. With Bs development, weak interactions between mineral surfaces and OM appeared, while at a later stage OM differentiated into bulky structures and tightly bound, rigid ones, with extremely low N2 accessibility. The latter were not sensitive to low concentration NaClO while the former were easily oxidised.

Stable isotope C analysis is the most reliable method used for the distinction and understanding of soil carbonates origin. However, in soils with a complex geological setting the carbonate δ 13 C signature could lead to incorrect interpretations if used alone. Thus coupling this technique to other methods may be necessary. In this work we evaluated advantages and disadvantages of several methods, some of which are well known while others are still unused, to distinguish among carbonates of different origins in a soil developed on “Valle Versa Chaotic Complex”, a marly geological formation in North-western Italy. For a better evaluation of their potentialities the methods were also applied to simpler situations used as a reference for carbonate of pedogenic and lithogenic origins. Thin sections analysis revealed the presence of three kinds of carbonates in the investigated complex soil: one was pedogenic, while two showed clear lithogenic origin. The lithogenic carbonate that showed a low δ 13 C (about − 9‰) was interpreted as freshwater while isotopic signature increased up to − 4‰ with the presence of marls, thus no evidence of pedogenic precipitations could be obtained with isotopic analysis. The mean crystallite domain ( L 104 ) was highly variable and related to the amounts of co-precipitated impurities in the carbonates. Thus these methods provided important information about the formation environment. These rarely used techniques permitted to distinguish between pedogenic and lithogenic material in simple systems, but did not adequately support the presence of pedogenic carbonates in the complex soil. Surface areas and porosity evaluated by N 2 adsorption are particularly influenced by the processes occurring during calcification such as the development of coatings and pore infillings. The comparison between additive models and measured specific surface area, indeed allowed us to observe the effect of pedogenic carbonate on the physical properties, although it did not permit any quantification. These results indicated that, although all the methods were able to distinguish between pedogenic and lithogenic origins in simple systems, only micromorphology and N 2 adsorption techniques allowed for the identification of pedogenic carbonate in a more complex soil system.