Tracking Water Sources and Root Water Uptake of Boreal Trees on Fluvioglacial Deposits: Perspectives from Stable Isotope (reescheduled)

Global warming in boreal forests is more pronounced than elsewhere, as temperature is increasing twice as fast as the rest of the planet. Low water availability in some boreal forest stands is one of the numerous consequences of increasing temperature. Sites with coarse surficial deposits where water drains fast are more vulnerable to water stress, such as sites on esker fluvioglacial deposits. The eskers of the Abitibi region of Quebec (Canada) are valuable ecosystem for wood provision and water recharge but are easily susceptible to water stress. Understanding the interplay between forests on eskers and water is crucial to develop effective conservation strategies for these ecosystems. This study aims to track the water sources and the root water uptake of the soil-plant-atmosphere continuum in the Saint-Mathieu Berry esker of the Abitibi region using stable isotopes of hydrogen and oxygen (δ2H & δ18O). Rainfall, snowpack, groundwater, plant xylem, and soil samples will be collected between April and November from the saturated and unsaturated zone of the esker. Plant and soil water will be extracted using cryogenic vacuum distillation, and isotopic ratios will be measured with an isotope ratio mass spectrometer. The Bayesian mixing model MixSIAR will be used to analyse the contributions of source water to the plant isotopic composition and to quantify the depth of root water uptake.  We expect water uptake from the upper soil at the beginning of the growing season and a shift to deeper soil water utilization at the end of the growing season. The outcome of this study will provide a better understanding of plant-soil water interactions and of forest responses on esker to hydroclimatic changes linked to global warming.