BOOK OF ABSTRACTS 249 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Environment, Agriculture, and Forestry P4.20 Linking Vegetation Cover, Soil Phosphorus Fractions, Enzyme Activity, and Contaminant Interactions Mónica Antilén1,2, Maria Cayupan1, Aurora Baeza1, Eduardo Arellano2,3, Angela Hernandez4 1 Pontificia Universidad Católica de Chile, Facultad de Química y de Farmacia, Vicuna Mackenna 4860, Santiago, Chile, mantilen@uc.cl 2 Pontificia Universidad Católica de Chile, Instituto para el Desarrollo Sustentable, Vicuna Mackenna 4860, Santiago, Chile 3 Pontificia Universidad Católica de Chile, Facultad de Agronomía y Sistemas Naturales, Vicuna Mackenna 4860, Santiago, Chile 4 Centro de Investigación en Ecosistemas de la Patagonia, Chile The intensive use of veterinary antibiotics and the increasing occurrence of forest fires associated with climate change are major pressures on volcanic soils in southern Chile, where phosphorus (P) is a key limiting nutrient. This study evaluated the distribution of P chemical fractions, acid phosphatase activity, and the influence of sulfamethoxazole (SMX) in Andisol soils under different vegetation covers: mature and secondary lenga forest, postfire lenga regeneration, and post-fire grasslands. Soils were physicochemically characterized (pH, organic matter, Olsen P, mineral N, exchangeable cations, exchangeable Al, and CEC). Phosphorus fractionation was performed by sequential extraction, distinguishing inorganic (acidic and basic) and organic (humic and fulvic) fractions. Acid phosphatase activity was determined spectrophotometrically based on p-nitrophenol release, in the absence and presence of SMX. Statistical analyses included hypothesis testing (α = 0.05), correlations, and principal component analysis (PCA). Results revealed that vegetation cover influences soil physicochemical properties, while preserving typical Andisol traits such as high organic matter content and acidic pH. Organic P accounted for a substantial proportion of total P, whereas acidic inorganic P predominated. Organic P and fulvic fractions were positively correlated with exchangeable Ca, Mg, and K, and negatively correlated with exchangeable and extractable Al, highlighting Al-driven P immobilization. Acid phosphatase activity varied among vegetation covers. The presence of SMX did not produce significant differences over time compared to control conditions. These findings provide an integrated view of P dynamics in volcanic soils under contrasting vegetation covers and suggest that variability persists even within the same cover type, with
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