Interaction effects of vegetation type and Pacific madrone soil inocula on survival, growth, and mycorrhiza formation of Douglas-fir

on survival, growth, and mycorrhiza formation of Douglas-fir. Can. J. For. Res. 19: 550-556.
Douglas-fir seedlings were planted in cleared blocks within three adjacent vegetation types, whiteleaf manzanita,annual grass meadow, and an open stand of Oregon white oak, in southwest Oregon. Within subplots in each block,either pasteurized or unpasteurized soil from a nearby Pacific madrone stand was transferred to the planting holesof the seedlings; control seedlings received no madrone soil. Second-year survival averaged 92, 43, and 12% for seed-lings planted on the manzanita, meadow, and oak sites, respectively. Growth differences generally paralleled survivaldifferences. Added madrone soil, whether pasteurized or unpasteurized, did not influence survival, but growth of seed-lings on the manzanita site was substantially increased by the addition of unpasteurized madrone soil. Unpasteurizedmadrone soil did not influence growth of seedlings in the meadow and the oak stand. Pasteurized madrone soil didnot affect growth in any of the vegetation types. When added to the manzanita site, unpasteurized madrone soil nearlytripled the number of mycorrhizal root tips forming on seedlings and resulted in formation of a new mycorrhiza typenot seen otherwise. As with growth, unpasteurized madrone soil had little or no effect in the other vegetation types.These results suggest that manzanita and madrone impose on soils a biological pattern that stimulates Douglas-fir growthand survival, and they add to the growing body of literature showing that root symbionts and rhizosphere organismsmediate interactions among plant species.