FACTORS AFFECTING THE INOCULUM POTENTIAL OF VA AND ECTOMYCORRHIZAL FUNGI IN FOREST SOILS OF SOUTHWEST OREGON AND NORTHERN CALIFORNIA.

摘要

Seedling bioassays were conducted in the greenhouse to determine if the inoculum potential of VA and ectomycorrhizal fungi in forest soils is affected by logging disturbance, soil temperature, drought, or removal of organic matter.;Root zone temperature affected mycorrhizal colonization on Douglas-fir, ponderosa pine and subterranean clover. Maximum formation of both VA and ectomycorrhizae occurred at 18.5 - 24(DEGREES)C; there were no significant qualitative or quantitative differences between mycorrhizae developing in soils from recently clearcut sites and undisturbed forest stands. Mycorrhiza formation was moderate even at the lowest temperature tested (7.5(DEGREES)C), but was greatly diminished or prevented at 29.5(DEGREES)C. Propagules of ectomycorrhizal fungi tolerated prolonged treatment at 35(DEGREES), but young mycorrhizae were injured by high temperature.;With net photosynthetic rate as an indicator of plant moisture stress, ectomycorrhizal Douglas-fir seedlings conditioned to cyclic drought tolerated and recovered from stress more quickly than nonmycorrhizal seedlings; net CO(,2) fixation of mycorrhizal seedlings was 10x greater than that of nonmycorrhizal seedlings. Four mycorrhizal fungi were compared for their ability to improve host drought tolerance. Seedlings inoculated with Rhizopogon vinicolor were less affected by drought than other mycorrhizal or nonmycorrhizal treatments. In vitro growth of mycorrhizal fungi in nutrient solutions osmotically adjusted with polyethylene glycol was a poor indication of effectiveness in reducing plant moisture stress in vivo.;Western red cedar grown in soil from disturbed clearcut sites were highly mycorrhiza dependent (1400%), more so than in soil from adjacent nondisturbed forest sites. Glomus tenuis was the most abundant endophyte. Douglas-fir was less mycorrhiza dependent (145%).;Inoculum potential of fungi forming ectomycorrhizae with Douglas-fir and ponderosa pine was less in soils from old clearcuts than in soils from adjacent undisturbed forest stands; it was further reduced in soils from clearcuts which had also been burned.;Forest floor organic matter contained inoculum of VA and.;ectomycorrhizal fungi. Application of litter to seedlings resulted.;in growth enhancement beyond the effects of mycorrhizal inoculum.;or addition of nutrients, suggesting the presence of microorganisms.;stimulatory to plant growth and/or activity of mycorrhizal fungi.;*All degree requirements completed in 1982, but degree will be granted in 1983.