The influence of soil physico-chemical properties and land uses on organic carbon stocks in contrasting Mediterranean pedosystems

Soil plays a pivotal role in the processes and behavior of the global carbon cycle, with soil organic carbon stocks (SOCs) representing the largest terrestrial carbon (C) pool. Mediterranean areas are among the world's biodiversity hotspots for conservation priorities. The island of Sardinia (southern Italy), due to the rare convergence of environmental and historical land use factors, is characterized by extremely peculiar soil conditions. This study investigated SOCs and their behavior in two contrasting Mediterranean pedosystems: Cambisols developed on granite (the most common pedosystem) vs Luvisols on limestone (one of the rarest), featuring different land covers with a gradient varying from agricultural (vineyard at different ages) to more natural areas (remnants of natural potential vegetation cover). Several soil physico-chemical features were assessed. An ANOVA was conducted to determine significant differences ( p < 0.05) between and among investigated horizons and land uses. The variability and complex multiple relationships were analyzed by factor (FA) and principal component analysis (PCA). Results revealed that areas with natural or near-natural features exhibited significantly higher SOCs compared to more intensively managed and human-influenced land covers. Interestingly, the two investigated pedosystems, originating from diverse substrates and thus contributing to different soil formation processes, are characterized by significantly different SOC amounts and behaviors. Overall, soil features have a greater influence on SOCs than usually expected and previously reported. Consequently, this study suggests that SOC investigations, if not conducted in conjunction with a thorough soil analysis, may lead to inaccurate or misleading outcomes and subsequent conclusions.