Isotopic insights into the dynamics of soil water pools along an elevation gradient

Abstract. Recent intensive research on the soil–plant–atmosphere continuum has introduced novel methodological approaches. These include new in-situ extraction techniques and the application of stable hydrogen and oxygen isotopes in water, which enable tracing of water movement and plant responses at much finer spatial and temporal scales. Such approaches provide detailed insights into soil water dynamics and plant adaptation to changing environmental conditions under climate change. This study aims at an intimate description of dynamics of distinct soil water pools—mobile versus tightly bound water—along an elevation gradient, together with the impact of the absence of snow accumulation in lowland areas on water distribution within the soil profile compared to higher elevations. In contrast to conventional bulk water sampling, the key innovation of this research lies in the novel extraction method that selectively isolates tightly bound soil water for isotopic analysis, combined with a unique experimental design encompassing sites across the elevation gradient. Our results indicate a prolonged residence time of winter-derived soil water in lowland sites, despite limited snow cover, contrasting to a rapid turnover at the highest elevation, where the winter water signal dissipated shortly after snowmelt. Simultaneously, distinct isotopic compositions among water pools—mobile versus tightly bound water—were also found, especially in lowland areas at the edges of the growing season (up to 3 ‰ and 21 ‰ for δ18O and δ2H, respectively), while tightly bound and bulk soil water exhibited—on average—only minor or no isotopic differences. Facing the projected continued decline in snow cover at higher elevations in Central Europe, these findings are critical for improving predictions of soil water storage and, consequently, plant water availability under ongoing climate change.