Modification of root IAA concentrations, tree growth, and survival by application of plant growth regulating substances to container-grown conifers ∗

Abstract

Tree survival after planting is partially a function of the tree's capacity to produce new roots. In a field trial we assessed the potential to modify the IAA concentration in roots, root growth responses, and plant survival by root application of plant growth regulators (PGRs) such as IBA, NAA, and ethylene, or alginate, a moisture retention material. Container-grown Douglas-fir, Englemann spruce, and lodgepole pine were lifted before and during prescribed lifting windows and treated with Stim-root ,E threl, Hormogel , or alginate before or after cold-storage, then planted in a clearcut. Lifting trees outside of the prescribed lifting window decreased IAA concentrations in roots of Douglas-fir, Englemann spruce, and lodgepole pine. Treating plants with different PGRs after cold storage increased root IAA concentrations and root growth after planting compared to treating plants prior to cold storage. Root growth and above ground plant growth and survival were well correlated to IAA concentrations in roots of Douglas-fir and Englemann spruce. IAA concentrations in roots of lodgepole pine correlated with root growth, but did not correlate with survival. A cost analysis of treatment effects on growth and survival showed that certain post-cold storage PGR treatments can decrease the cost necessary to attain target stocking and increase the size of the trees. Our results suggest that application of PGRs or other root-promoting materials to tree roots before planting has the potential to be a cost-beneficial method for increasing root growth and tree survival.