BOOK OF ABSTRACTS 191 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Soil Organic Matter, Caustobiolites, and Biochar P2.2 Organic Matter Transformation and Dynamics of Phosphorus Forms in Eutrophic and Dystrophic Terrestrial Ecosystems under Different Moisture Conditions Magdalena Debicka, Adam Bogacz, Aleksandra Samol Wrocław University of Environmental and Life Sciences; Institute of Soil Science, Plant Nutrition and Environmental Protection, Grunwaldzka 53, 50-357 Wrocław, Poland, e-mail: magdalena.debicka@upwr.edu.pl The key role of soil organic matter (SOM) in determining soil quality and its impact on nutrient cycling, particularly phosphorus (P), is increasingly recognised in the context of global climate change and anthropogenic pressures. Accelerated degradation and mineralisation of SOM causes a significant decline in soil quality and also affects phosphorus transformations in the soil environment, highlighting the need to understand the processes of organic matter (OM) transformation and their impact on phosphorus availability and retention. This presentation delves into the complex interactions between OM transformation and P dynamics in eutrophic and dystrophic terrestrial ecosystems, with a specific focus on peatlands (Histosols), which are vital global carbon reservoirs but highly sensitive to environmental alterations and key to understanding OM-driven biogeochemical cycles. Our study investigated P dynamics in Histosols from the Oder Valley, southwest Poland, representing both eutrophic and dystrophic conditions [1,2]. We employed methods to determine various P forms, including organic P (Po), available P (PM3), watersoluble P (PW), easily soluble P (PCaCl2), and organic P fractions in humic (Po_HA) and fulvic (Po_FA) acids. Results indicate that OM transformation significantly influences P retention and the content of its various forms. Increased microbial activity, especially in eutrophic habitats, led to more pronounced OM mineralization and humification, resulting in higher levels of available and soluble P in upper organic horizons. Conversely, P release was slower in dystrophic conditions due to P immobilization by Al and Fe oxides at lower pH, and reduced chemical activity of OM components. Humic substances played a key role in P retention, with Po_HA dominating in dystrophic peat horizons, while Po_FA increased with OM transformation in eutrophic soils. This suggests a variable, context-dependent role of different OM constituents in P dynamics. Understanding these ecosystemspecific mechanisms of OM-P interaction is vital, not only for the conservation of P-rich natural areas like peatlands (where
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