Light-Use Efficiency and Photosynthetic Capacity of Northern White-Cedar (Thuja occidentalis L.) Cuttings Originated from Layering and Seed

Northern white-cedar (Thuja occidentalis L.) regeneration originating from layering is generally considered to be more shade tolerant than that of seed origin. In this study, we examined photosynthetic light-use efficiency, an important component of shade tolerance, of these two forms of regeneration using light-response curves of 1-year-old rooted cuttings of layers and seedlings grown under low (20% of full sun) and high (90% of full sun) light conditions. Northern white-cedar showed a strong potential for photosynthetic acclimation to light availability, as indicated by significant differences in the light compensation point (LCP), dark respiration (R d ), apparent quantum efficiency (PE), and light saturation point (Q sat ) but not light-saturated rate of net photosynthesis (A max ) between cuttings grown under high and low light. Values of Rd, LCP, and PE did not differ between layers and seedlings grown under high and low light, but layers had higher Amax and Qsat than seedlings when grown under high light. This result may reflect a comparatively lower capacity for photosynthetic acclimation of seedlings to high light conditions, perhaps because of their younger physiological age. A lower capacity for photosynthetic acclimation to light in seedlings could limit the repair and recovery of their photosynthetic systems from damage associated with the more extreme microenvironments of open, recently disturbed sites.