EFFECTS OF SHADE AND ROOT CONFINEMENT ON THE EXPRESSION OF PLAGIOTROPIC GROWTH IN JUVENILE-ORIGIN DOUGLAS-FIR ROOTED CUTTINGS

The purpose of this experiment was to determine why juvenile-origin Do uglas-fir (Pseudotsuga menziesii (Mirb.) France) rooted cuttings, whic h remain plagiotropic (branchlike) when grown in containers in shaded glasshouses, become orthotropic (vertical) after they are transplanted to an outdoor environment. Plagiotropic rested cuttings (mean angle f rom vertical = 45-50 degrees) from three full-sib families were transp lanted into an outdoor nursery and subjected to four treatments consis ting of a factorial of (1) shaded or unshaded and (2) bareroot or conf ined roots. After two growing seasons, treatments had significantly af fected plant size and biomass in the order unshaded-bareroot > shaded- bareroot > unshaded-confined > shaded-confined, but plants in all trea tments had become nearly orthotropic. It is concluded that neither sha ding nor root confinement is, but other glasshouse environmental condi tions are, responsible for the persistence of plagiotropic growth.