Photosynthesis and growth of Douglas-fir seedlings when grown in different environments

Abstract

Douglas-fir seedlings from western Montana and western Oregon seed sources were grown in a cool (18 °C day – 4 °C night) or warm (36 °C day – 21 °C night) growth chamber. Photosynthetic and respiratory rates were measured at 20°, 27.5°, and 35 °C at cotyledon stage (15 to 18 days old), 55 days old, and 100 days old. Needle, stem, and root dry weights were also determined. Photosynthetic rates declined with age, were higher for Oregon than for Montana seedlings, particularly at lower measurement temperatures, were higher for high-temperature-grown than for low-temperature-grown plants, and were lowest at the highest measurement temperature. Each of these factors was modified by the others in its effect on the photosynthetic rates. Respiration rates declined with age, were slightly higher for Montana than for Oregon seedlings, were much higher for the cold-temperature-grown than for the warm-temperature-grown seedlings, and were highest at the highest measurement temperature. When plants from the two growth environments were interchanged, the photosynthetic rates (measured at 27.5 °C only) of the seedlings changed to those of the new environment within 10 days. Comparison of seedlings grown at high and low temperatures showed the latter to have lower photosynthetic rates but higher growth rates, probably as a result of the higher proportion of leaf tissue produced by the low-temperature-grown plants.