Influence of snow cover and microclimate on soil organic carbon stability in European mountain grasslands

• Microclimate significantly influences SOC properties in mountain grasslands. • Longer freezing season increase SOC content but decrease biogeochemical stability. • Longer growing seasons increase SOC stability in intermediate grasslands. • Thermal indices of SOC stability indicate higher lability at higher elevations. • Soil pH and water regime influence SOC properties. Soil organic carbon (SOC) is crucial for ecosystem function and carbon storage, especially in mountain regions where cooler temperatures limit microbial activity, leading to higher SOC stocks compared to lowlands. However, the available data are insufficient to fully understand the distribution of SOC properties along elevation and snow cover duration gradients. Given that climate change models predict a reduction in snow cover duration, it is essential to better characterize these properties at a finer, mesotopographic scale (e.g., ridges and slopes), corresponding to the distribution of mountain plant communities. This study investigates the impact of microclimate on SOC content and stability in European mountain grasslands. We focused on two types of grasslands on acidic soils to maintain homogeneity in key parameters such as soil properties and plant communities. These grasslands, located across temperate European mountain ranges (Alps, Pyrenees, Vosges, Balkans, Carpathians, Black Forest, Bohemian Forest, and Sudetes), span a gradient of snow cover duration, ranging from frost-exposed ridges dominated by Carex curvula , to intermediate grasslands, without frost, dominated by Nardus stricta . SOC content and stability were assessed using Rock-Eval® thermal analysis across all sites. The results indicate that microclimate significantly influences SOC properties. Cooler temperatures, driven by elevation and reduced snow cover duration, were associated with increased SOC content but decreased stability. On windy ridges, extended growing seasons combined with intense winter freezing led to higher SOC lability, as freezing slows down mineralization processes. In contrast, intermediate grasslands, with longer growing seasons, showed enhanced SOC stability due to higher decomposition activity. These findings provide valuable insights into how SOC properties may evolve under climate change, particularly in relation to rising temperatures and shifting snow cover dynamics.