ECTOMYCORRHIZAS AND RHIZOSPHERE MICROORGANISMS OF SEEDLINGS OF PSEUDOTSUGA-MENZIESII (MIRB) FRANCO PLANTED ON A DEGRADED SITE AND INOCULATED WITH FOREST SOILS PRETREATED WITH SELECTIVE BIOCIDES

Inoculation of planting holes with small amounts of soil from a mature forest or a plantation can improve formation of ectomycorrhizas on Ps eudotsuga menziesii (Mirb.) France seedlings in degraded clearcuts in southwestern Oregon. To determine the component(s) of transferred soil responsible for increased ectomycorrhiza formation, we treated soil f rom a clearcut, a mature forest, and a plantation with one of the foll owing: fertilizer to test for the effect of nutrients, dimethoate and carbofuran to test for the effect on microarthropods or nematodes, fum agillin to test for the effect on protozoa, captan to test for the eff ect on fungi, penicillin and oxytetracycline to test for the effect on bacteria, pasteurization to test for the effect of active forms of or ganisms, Tyndallization to test for the effect of resting forms of org anisms, or water as a control. We studied the effect of inoculation wi th soil subjected to these treatments on number and types of ectomycor rhizas, and length of active mycelium, and number of active bacteria i n the rhizosphere. Inoculation with untreated forest or plantation soi ls increased the number of ectomycorrhizas but did not change the myco rrhizal types present. Most agents had different effects in different soils. Inoculation with pasteurized and Tyndallized clearcut and plant ation soils increased the number of Rhizopogon- and Thelephora-type ec tomycorrhizas and decreased the number of active bacteria, as did untr eated forest soil. We hypothesize that the role of the soil transfer i s to provide a rhizosphere environment free from a deleterious organis m present in the clearcut. In this environment, beneficial organisms p resent in the clearcut or brought in with the seedling from the nurser y can proliferate.