Intraspecific Variation in Regulation of Water Status and Cold Acclimation in Interior and Coastal Douglas-fir in Response to Simulated Warmer and Drier Climate

Climate change in northern forests is causing increased water stress during summer droughts and potentially increased frost vulnerability following warmer autumns. Physiological responses to changing climate may vary among populations of tree species with broad ranges, such as Douglas-fir (Pseudotsuga menziesii). We aimed to characterize intraspecific variation in the responses of interior and coastal Douglas-fir to summer drought and autumn warming. We assessed photosynthesis, water use efficiency, xylem function, and freezing tolerance in seedlings under controlled conditions. Interior populations exhibited hydraulically safer but less efficient xylem whereas coastal populations exhibited more hydraulically efficient but less safe xylem. Differences in photosynthesis were minimal but suggested lower drought tolerance in the most coastal population. Autumn warming delayed downregulation of photosynthesis, however this did not impair development of freezing tolerance. This research will help determine which tree populations are best adapted to future warmer and dryer climates and thus improve forest regeneration efforts.M.Sc