As northern ecosystems warm, precipitation regimes change and vegetation shifts, there is limited knowledge of how changing plant composition will affect critical zone water fluxes across cold regions. Here, we use stable water isotopes to assess the role of soil moisture, precipitation dynamics, and plant species on the timing, magnitude, and sources of plant water uptake across a subarctic, alpine catchment in Yukon, Canada. We sampled soil and xylem water every 3 weeks over 2 hydrologically distinct years at a low elevation boreal forest site, and two high elevation shrub sites of varying shrub heights and densities. We answer the questions: 1) What are the seasonal and interannual changes in the isotopic composition of soil and xylem water? 2) Where in the soil profile do subarctic plants access water within and among seasons? and 3) How does the seasonal origin of xylem and soil water across a range of subarctic vegetation covers? While volume weighted precipitation became more depleted with elevation, the opposite was true in xylem water. Plant water uptake was more reflective of snow water at the forest site than both shrub sites. Near-surface soil water had more negative lc-excess at the forest throughout the season and with depth, highlighting increased contributions from soil evaporation. Mixing analyses revealed that subarctic plants were opportunistic, using both snow and rain dependent upon season and timing of precipitation. Results suggest that the concurrent changes in vegetation and precipitation regimes will have considerable impact on future blue/green water fluxes.