Role of roots in winter water relations of Engelmann spruce saplings

Roots play a role in maintaining foliar water balance in subalpine conifer saplings during winter. We used deuterium-labeled water to demonstrate that roots of Engelmann spruce (Picea engelmannii Parry) take up water during the late-winter-early spring period. Based on a root severing experiment, we conclude that small, snow-covered saplings were largely dependent on root water uptake to meet winter transpiration needs, whereas larger saplings relied more on water stored in stem sapwood. Both water uptake and water stored in roots appeared to be critical for the survival of saplings exposed above the snowpack during the late-winter-early spring period, when sap reserves were insufficient to meet increasing transpirational demands.