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 enabling to trace 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 to provide a comprehensive characterization of dynamics of distinct soil water pools - mobile versus tightly bound water - along an elevation gradient, while simultaneously assessing the impact of the absent snow accumulation in lowland areas on soil water distribution compared to higher elevations. In contrast to conventional bulk water sampling, a key innovation of this study lies in the experimental design across the elevation gradient combined with a novel extraction method that selectively isolates tightly bound soil water for isotopic analysis. The results indicate a prolonged residence time of winter-derived soil water in lowland sites, in contrast to a rapid turnover at the highest elevation, where the winter water signal dissipates shortly after snowmelt. Distinct isotopic compositions among water pools - mobile versus tightly bound water - were particularly evident in lowland areas at the edges of the growing season (up to 3% and 21% forδ18O andδ2H, respectively), while tightly bound and bulk soil water exhibited - on average - only minor or no isotopic differences. In the context of 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.