A pedo-isotopic approach to study sandy soils of the Brazilian Cerrado in Piauí State

Sandy soils dominate Brazil's Cerrado biome in Piauí State, yet their organic carbon (OC) stabilization mechanisms and landscape-driven pedogenesis remain poorly understood. To clarify this topic, the present study proposes a pedo-isotopic approach to characterize six representative Brazilian Cerrado soils derived from sedimentary rocks in Piauí State and improve the understanding of the effects of landscape on the source of OC, dynamics of organic matter, mineralogy of the clay fraction, and stabilization of OC in this environment. To achieve these goals, we assessed the morphological, physical, chemical (including stable isotope ratios of carbon [δ¹³C] and nitrogen [δ¹⁵N]), and mineralogical attributes of samples collected from six soil profiles representing regions of the Parnaíba and São Francisco Sedimentary Basins. Results revealed that C₃ plants were the primary OC source (δ¹³C: −27‰ to −22‰), with plateau soils retaining more C₃-derived OC due to mineral-organic interactions. We also observed that Al₂O₃ in clay fractions correlated strongly with δ¹³C and δ¹⁵N, indicating its key role in OC stabilization. Another important finding was that the isotopic boundaries distinguished sub-environments, with plateau soils showing higher Al₂O₃ and OC stability than foot slopes. The absence of gibbsite highlighted unconventional pathways for Al₂O₃-OC associations in sandy soils. We conclude that the proposed pedo-isotopic approach is an accurate alternative method for investigating the effects of landscapes on the source and stabilization of OC, dynamics of organic matter, and clay mineralogy.