Changes in Interior Douglas-Fir Root Development in Containers after Copper and Auxin Treatments

Abstract

Growing interior sources of Douglas-fir (Pseudotsuga menziesii var. glauca) seedlings in containers with four root-modifying treatments changed root morphology and subsequent abundance and location of new roots. Copper, 1-napthaleneacetic acid (NAA), and copper + NAA treatments reduced height and shoot biomass about 20% compared with the control, but root collar diameters were similar. In a root growth chamber, however, 30% more new roots occurred in the copper treatment compared with the control, and new roots originating in the upper portion of the root plug increased 3X. NAA increased the total number of new roots and roots growing from the upper root plug when compared with the control but not to the same extent as copper. Combining copper and NAA decreased the number of deliverable seedlings by about 50% when compared with all other treatments.