摘要：Photoperiod manipulation by artificial short-day treatment (blackout) is increasingly used as a tool to induce dormancy in nursery-grown seedlings. This article summarizes preliminary results from a project to evaluate optimum blackout protocols for Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings. We subjected seedlings to three blackout intensities (mild, moderate, and long) and compared morphological and physiological responses at the time of lifting and during the next growing season with seedlings in a control treatment (ambient day length) and a progressive blackout treatment involving a gradual reduction of light during the hardening phase. We additionally characterized morphology, bud break, and root growth in response to varying rhizosphere temperatures. Preliminary results indicate that seedlings subjected to blackout treatments had earlier bud break in both a controlled hydroponic culture and a field plot. Seedlings from the mild, moderate, and long blackout treatments had less root growth in the hydroponic trial but greater early spring shoot and root biomass in the field plot. By the end of the growing season, however, biomass in the field plot did not differ among treatments. Cold hardiness was unaffected by treatments. Additional results from this trial and another trial to examine blackout effects on varying seed sources will be published at a later date. This paper was presented at the annual meeting of the Western Forest and Conservation Nursery Association (Eugene, OR, October 26–27, 2015).
