BOOK OF ABSTRACTS 143 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C Soil Organic Matter, Caustobiolites, and Biochar SL69 Linking Thermal Stability of Soil Organic Carbon to Water Repellency of Forest Floor and Topsoil in a Mixed Oak–Beech Forest Tomáš Vichta1, Radek Bydžovský1, Jiří Volánek1, Aleš Kučera1 Mendel University in Brno, Department of Geology and Soil Science, Zemědělská 3, 613 00 Brno, Czech Republic, tomas.vichta@mendelu.cz Soil water repellency (SWR) is a widespread phenomenon in all terrestrial ecosystems and has traditionally been regarded as a negative soil property, as it promotes preferential flow and surface runoff, thereby increasing the risk of soil erosion [1]. However, a growing body of evidence suggests that SWR may also fulfill important ecological functions, including enhancing the resilience of plant and soil microbial communities, as well as stabilizing soil organic carbon pools under environmental stress, particularly during drought and post-fire conditions [2,3]. The occurrence and severity of SWR are closely linked to both the quantity and composition of soil organic matter, which comprises a wide range of organic polymers and waxes derived from plant material at different stages of decomposition. Nevertheless, the specific characteristics and distribution of these compounds in soils remain understood [4,5]. In this context, recent studies have demonstrated that temperature-dependent carbon fractionation (DIN 19539 standard [6]) enables a detailed characterization of distinct soil organic carbon pools [7,8]. These approaches also allow the derivation of thermal indices of soil organic matter that reflect its composition and are related to the origin and transformation of plant detritus mediated by soil micro- and macroorganisms [9]. We applied this approach to 108 forest floor samples and 216 topsoil samples (0–5 cm and 5–15 cm layers) collected from a mixed oak–beech forest. The aim was to investigate the thermal behavior of soil carbon in relation to the occurrence and severity of SWR across these samples. Our results confirmed the presence of three distinct soil carbon pools with different thermal stabilities, consistent with previous findings from agricultural soils [9]. These include thermally labile organic carbon (TOC400), residual oxidizable carbon (ROC), and total inorganic carbon (TIC900), corresponding to temperature ranges of 300–400 °C, 510–600 °C, and 700–900 °C, respectively. At the same time, a pronounced vertical gradient in SWR was observed: the forest floor was dominated by strong to extreme repellency classes, the 0–5 cm layer was mainly
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