Root growth in Sitka spruce and Douglas-fir transplants: dependence on the shoot and stored carbohydrates.

When dormant Sitka spruce (Picea sitchensis (Bong.) Carr.) transplants were lifted from the nursery in March and transferred to favorable growing conditions in a controlled environment chamber, new roots emerged and elongated even when the plants were bark-ringed so that the roots could not receive metabolites from the shoot by phloem translocation. Carbohydrate analysis showed that starch reserves in the roots of the bark-ringed plants were depleted, indicating that these reserves provided the energy source for new root growth. The shoot also had a role in new root growth as excised root systems showed greatly reduced root growth. This response is compared to that of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in which bark-ringing prevented root growth indicating that current photosynthate is needed for new root growth. The findings are discussed in relation to the problems of establishing these species in forest plantations.