BOOK OF ABSTRACTS 175 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Friday, 28 August 2026 / Hall C Travel Awardee Presentations O-Alkyl and a decrease of Alkyl C and of Aromatic C proportions. Biogenic aggregates contributed proportionally more to aggregateassociated TOC in the surface layer, particularly under U. brizantha (38%), indicating a stronger influence of plantdriven aggregation near the soil surface. In contrast, at 0.05–0.10 m increased contributions of physicogenic (43% in C. dactylon, 38.5% in H. altissima and 36.7% in U. brizantha) and decompressive aggregates (39.2% in C. dactylon, 38.5% in U. brizantha and 33.9% in H. altissima), reflecting a different aggregation pathway compared to surface layers. Compressive aggregates contributed minimally to TOC across all treatments (0%–7.3%), confirming that such aggregates result from compaction of minesoil during landscape shaping after mining activities, and not from biological processes mediated by plants and microbes. The combined analysis of aggregateassociated TOC and soil chemical composition indicates that plantderived, carbohydrate-rich carbon under U. brizantha is preferentially incorporated into soil structure through biogenic aggregation in surface layers in comparison to the other two grasses. In general, subsurface layers are dominated by physicogenic and decompressive pathways, which are primarily associated with the physical redistribution and stabilization of soil organic carbon rather than with recent plant-derived inputs. This is corroborated by the higher contribution of grass-derived carbon under U. brizantha, suggesting more effective soil reaggregation compared to the other grasses and supporting the predominance of biogenic aggregation driven by root-derived organic matter, as indicated by the high O-alkyl content. We found that carbon allocation in minesoils is controlled by the interaction between aggregation pathways and organic matter transformation, with root-derived inputs and O-alkyl-rich organic matter under U. brizantha being preferentially incorporated through biogenic reaggregation, which showed the highest contribution of aggregateassociated total organic carbon. Acknowledgement The authors thank the Companhia Riograndense de Mineração for logistical assistance, and CAPES and CNPq for financial support allowing the realization of this work.
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