In South America, pre-Columbian cultures were responsible for the formation of two types of anthropogenic soils: Dark-Earths (DE) and Shellmounds (SM), both characterized by high nutrient content, especially phosphorus (P), in contrast to the surrounding natural soils. Previous work has reported high total P content in DE, while SM have hardly been studied. In this study, 75 samples from different geographical locations were analyzed: 38 tropical, equatorial and sub-polar SM; 30 tropical-equatorial DE; and 7 control soils (CS), to improve our comprehension of P dynamics. Geochemical forms of P were investigated using sequential chemical extraction and 31P NMR. The results revealed significant differences between natural soils and Anthrosols. Control soils showed lower pH (4.3 ± 0.3), lower total organic C (0.5 ± 0.1%) and total N (0.03 ± 0.01%) than DE (pH:5.6 ± 1.6, TOC:1.6 ± 0.6%; TN:0.16 ± 0.18%) and SM (pH:7.2 ± 1.2, TOC:4.3 ± 4.3%; TN:0.24 ± 0.33%). Total P was markedly lower in CS (62 ± 84 mg·kg−1) than in DE (1028 ± 1043 mg·kg−1) and SM (12,812 ± 10,170 mg·kg−1). In control soils, P was mainly associated with recalcitrant organic matter, clays, and Al hydroxides, whereas Anthrosols displayed a more complex and variable distribution of P forms. In the acid DE samples, without carbonates, P distribution was similar to that of control soils. In contrast, carbonate-rich DE and SM were dominated by Ca-bound P, except for SM samples from the subpolar region, where P associated with humic substances was the predominant form. These findings highlight the edaphogeochemical anomaly of pre-Columbian anthropogenic soils, characterized by elevated total P and distinct geochemical forms. Differences in P speciation between CS, DE and SM soils reflect anthropogenic inputs and environmental drivers. Carbonate-rich environments promote Ca-bound P accumulation, whereas colder subpolar conditions favour organic-association P forms, indicating that climate-related factors may also influence P speciation across the different climatic regions studied. Overall, these results emphasize the functional divergence of DE and SM soils.
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