Geographic and seasonal variation in photosynthetic efficiency and capacity of Rocky Mountain Douglas-fir, Pseudotsuga menziesii var. glauca

Graduation date: 1978Net photosynthesis was measured for photosynthetic light efficiency and capacity on two-year-old plants from eight different seed sources in three measurement periods. The measurement periods corresponded to the physiological periods 1) prior to bud swelling, 2) after needle elongation, and 3) predormancy. Measurement period differences in both photosynthetic efficiency and capacity were apparent. The pre-bud swelling period had the lowest capacity and efficiency, the pre-dormancy period had the highest capacity and efficiency, and the intermediate period was between the two other periods in capacity and efficiency. Seven seed sources from regions within the Rocky Mountains and one hybrid of Coastal X Arizona origin represented populations from which seedlings were raised and measured. There were no apparent differences with respect to seed-source photosynthetic capacity. There were seed source related differences in photosynthetic light efficiency. The seedlings from the northern Rocky Mountain seed sources had a greater light efficiency than those from the southern-Rocky Mountains. These differences in photosynthetic light efficiency may be linked to summer drought adaption. The Lambert-Beers law type light intensity correction is promising in achieving a better estimate of photosynthetic light efficiency. This light intensity correction is based on the individual plant's morphology, needle number, needle length and needle area. Stomatal conductance was an important covariable in photosynthetic capacity. The light intensity correction and stomatal conductance accentuated seedling differences. This accentuation is viewed as the plant's adapting to the given set of conditions in the growing environment with physiological responses as well as developmental and/Or morphological responses