Lethal and Nonlethal Effects of the Organic Horizons of Forested Soils on the Germination of Seeds from Several Associated Conifer Species of the Rocky Mountains
The study tests whether the lethal effect of overwintering Engelmann spruce seed in its O-horizon affects Douglas-fir, lodgepole pine and subalpine fir seeds and whether the O-horizons of the three associated species have the same lethal effect on seeds. All seed treatments of each species were stratified in petri dishes in the pure O-horizon (unsterilized and autoclaved) of each species. Seed treatments were untreated, 10% slurry of 50% Captan and powdered 75% Captan.All untreated seeds demonstrated the lethal quality of unsterilized Engelmann spruce O-horizon. Its effects on untreated seeds and powder treated seeds were as follows: Engelmann spruce seed 3.5 and 77.3% (germination of untreated and powdered respectively), subalpine fir seed 1.3 and 20.8, Douglas-fir seed 9.5 and 84.8 and lodgepole pine seed 11.9 and 85.7. Subalpine fir O-horizon was lethal to its own seeds but only moderately harmful to seeds of other species. Douglas-fir O-horizon had a significant adverse effect on its own seeds and was only moderately harmful to seeds of other species. Lodgepole pine O-horizon was almost neutral to all seeds. Autoclaving of the O-horizons and powder treatment of seeds produced similar results.