Bioturbation and bio-geomorphic control of pedogenesis along a catena in the Atlantic Forest of southeastern Brazil

This study investigated soil processes along a catena under primary Atlantic Forest in southeastern Brazil. The role of biota in soil formation remains largely unaddressed at this region, a UNESCO World Heritage Site. This study innovatively investigates biological influences on pedogenesis along a representative catena . Three profiles were sampled at the crest, middle slope, and lower slope, where soils and litter were morphologically described, physically and chemically analyzed, and classified. Melanization in organomineral horizons was quantified using the Profile Darkening Index. The effects of root and earthworm bioturbation were characterized to evaluate biotic–abiotic interactions in soil formation. Bulk density varied from 0.53 g cm −3 (crest A horizon) to 1.72 g cm −3 (lower slope E horizon), while total carbon ranged from 123.5 g kg −1 (crest Oa) to 2.9 g kg −1 (lower slope E). Earthworm casts contained up to 77.1 g kg −1 C and enhanced nutrient contents (Ca 2+ : 0.7 cmol kg −1 ; Mg 2+ : 0.5 cmol kg −1 ). The combination of landform, water surplus, carbon input, and gneissic crystalline substrate creates a geochemical setting with strong leaching and acidity, where shallow soils develop. Organisms such as plants and earthworms play key roles in catena dynamics by enhancing infiltration, reducing erosion, and preserving organic matter, thereby directly influencing soil processes along the catena . Our findings demonstrate that organisms significantly affect pedogenetic processes across the hillslope. Integrating biotic–abiotic interactions is essential for interpreting tropical soil evolution and for guiding conservation strategies in Atlantic Forest environments under high denudation pressure. • Biological activity drives pedogenesis along the Atlantic Plateau catena. • Bioturbation affects soil formation across all topographic positions and horizons. • Pedogenic pathways vary downslope but are consistently modulated by biotic activity. • Soil evolution reflects bio-geomorphic feedbacks under intense leaching conditions. • Conserving soil biodiversity is key to soil stability and fertility in tropical landscapes.