MSc Exit Seminar – Devin Noordermeer (Ensminger Lab)

Climate change is threatening the health of northern forests due to increased water stress during summer droughts and potentially increased risk of freezing damage 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 therefore aimed to characterize intraspecific variation in the responses of interior and coastal Douglas-fir to summer drought and autumn warming. To accomplish this, 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 in all populations. However, this prolonged period of photosynthesis did not impair development of freezing tolerance, indicating that short daylength alone may be sufficient to induce cold hardiness in Douglas-fir. This research will help determine which tree populations are best adapted to future warmer and dryer climates and thus improve forest regeneration efforts.