Rapid root tip and mycorrhiza formation and increased survival of Douglas-fir seedlings after soil transfer

In order to re-inoculate soil with mycorrhizal fungi, small amounts (about 150 ml) of soil from an established Douglas-fir plantation were added to planting holes when Douglas-fir seedlings were planted on an old, unrevegetated clearcut in the Klamath Mountains of Oregon. Seedlings were lifted throughout the growing season to determine the influence of soil transfer on the rate of root tip initiation and mycorrhiza formation. Six weeks after planting, seedlings receiving plantation soil had formed 62% more root tips than controls; however, no statistically significant differences were apparent 15 weeks after planting. By that time, a small percentage of root tips were visibly mycorrhizal; seedlings receiving transferred soil had the most colonization (13.6 vs 3.5 per seedling, p 0.05). Of seedlings receiving transfer soil, 36.6% survived the first growing season, compared to 11.3% of control seedlings. At this high elevation, soils often remain frozen well into spring, leaving only a brief period betwen the time when soils become warm enough for root growth and the onset of summer drought. Under these conditions, the rapid root growth and mycorrhiza formation stimulated by plantation soil increases the ability of seedlings to survive the first growing season.This is Paper 2341 of the Forest Research Laboratory, Oregon State University.