Leveraging soil geochemistry and soil carbon dynamics at the Critical Zone and Ecosystem Observatory at Nivolet, Gran Paradiso National Park, Italy to project future alpine ecosystem functioning

Range shifts of alpine vegetation to higher elevation with warming are well-documented, but patterns of soil carbon (C) storage and development with warming remain unclear. Soil profiles under different topographic positions and geologic substrates were collected in the high-altitude, alpine pastures of the Nivolet Critical Zone and Ecosystem Observatory, Gran Paradiso National Park, Italy, to investigate the composition, distribution and controlling factors of organic C and weathering. Soil profiles were sampled to a depth of ~1 m across a range of parent materials deposited after the last glacial maximum, including gneiss glacial till, carbonate and calcschist/gneiss colluvium, and gneiss/carbonate/calcschist alluvium across ridgetop, midslope and footslope topographic positions. Organic C, C stable isotopes, major and trace element content, particle size distribution, and pH reveal how parent material and landscape position govern soil C storage and development. Even with the cold climate, limited season with liquid water, and young age, soils developed on gneiss and calcshist till and colluvium have developed insipient spodic horizons and include calcschist clasts that have completely weathered in place. Bulk geochemistry indicates the carbonate parent material is more weathered than the gneiss till and colluvium, but all parent materials show evidence of geochemical weathering. All soils have extensive belowground roots to at least 50 cm and organic C concentrations at the soil surface is ~10% in footslope position soils and ~5% in higher topographic positions, pointing to high biological inputs of C in these young soils. These data, in conjunction with microbial analysis and geochemical variation, suggest that biota are key agents promoting this degree of soil development in these high altitude soils. Carbon flux measurements at the soil-atmosphere interface reveal how C losses depend in part on parent material: where carbonate is present, C fluxes are more variable. We demonstrate how linking soil properties across parent material and topography with measures of C pools and fluxes reveal how soil development and C storage proceeds in the early stages of soil development.