The Influence of the Shoot on New Root Growth in Ponderosa Pine and Western Larch Seedlings
Harris, Ashley D.
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The relationship between the shoot and new root growth was examined during a test of root growth potential, with a special focus on clarifying the utilization of carbohydrates for new root growth. Four different treatments designed to influence root growth were applied to two-year-old ponderosa pine (Pinus ponderosa) and western larch (Larix occidentalis) seedlings from a bareroot nursery. Treatments were: 1) decapitation above the root collar (removing the living connection between the shoot and the root, preventing translocation of shoot and root material), 2) girdling below the root collar (preventing translocation of shoot substances to the root), 3) shading (placing hoods over the seedlings to eliminate the entry of light), and 4) control (no altering treatment). Measurements taken over the 29-day test period showed that new root growth in ponderosa pine and western larch utilized current photosynthate, as opposed to stored carbohydrates. The number of new roots, number of new roots longer than 1 cm, and days to root initiation were determined for the 29-day period. Girdling, growing seedlings without light, and decapitation inhibited or prevented new root growth. There was no statistically significant difference in the days to new root initiation between treatments. The control seedlings continued to increase numbers of new roots whereas the other treatments did not continue to produce new roots. The results of this study was used to evaluate seedling quality for greenhouse nursery management and reforestation efforts.