Root hydraulics under changing snow cover regime

Roots are essential plant organs responsible for anchoring, nutrient and water uptake to meet the needs of the transpiring canopy. Low soil temperatures can limit root growth and function and thus affect the water supply of trees. Roots and their hydraulics remain less understood than above-ground tree organs, especially for trees growing at higher elevations where temperature effects on roots are more pronounced. In the context of climate change, knowledge gaps become relevant as expected reductions in snow cover height and duration will expose roots not only to lower overall temperatures, but also to more pronounced temperature fluctuations and freeze-thaw (FT) cycles. The proposed project will address root ecophysiology in relation to changes in snow cover, with the following main objectives: (i) Analyzing the effects of reduced snow cover on root hydraulics and tree vitality via a snow manipulation experiment on stone pine and Norway spruce growing at the alpine treeline. (ii) Testing the effects of FT stress on root hydraulics of several alpine species by exposure to repeated FT cycles and/or drought stress, and on root systems of intact pine and spruce saplings by inducing consecutive drought, frost-drought, and recovery periods in controlled experiments. (iii) Analysis of the root hydraulic architecture and effects of winter stress of three alpine Pinus species growing at different alpine treeline regions in Europe. The project relies on a wide range of field and laboratory methods. Field methods include monitoring of embolism formation with ultrasonic emission analyses, studying freezing dynamics with infrared imaging or in-situ analyzing of xylem structures with electrical resistivity tomography of roots of different size classes and comparison with aerial roots and stems of similar size. In the lab, vulnerability to drought and FT stress induced xylem embolism will be analyzed using the optical and the centrifuge techniques, and cellular damage using the electrolyte leakage method. The results of the project will be of value for research on plant water relations in general and in particular for tree vitality and survival at higher elevation under climate change. The expected results will also be relevant for forestry and landscape management.