Graduate Thesis Or Dissertation
 

Management impacts on the ectomycorrhizal associations of Pseudotsuga menziesii var. menziesii seedlings : field and greenhouse bioassays

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m613n142j

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  • Field and greenhouse bioassays were used to compare the mycorrhizal associations of Douglas-fir seedlings from undisturbed forests, and nonburned and burned portions of clearcuts on three Sites in the west-central Cascades of Oregon. Field soil transfers and greenhouse soil pasteurization and reinoculation were used to investigate soil biology and inoculum potential. Similar mycorrhizal associations developed in soils from the three regeneration treatments in both field and greenhouse. Regarciless of soil origin, proportionately snore mycorrflizae developed in clearcuts (especially on site 2); the Brown mycorrhiza type was more frequent in nonburned clearcuts than in other treatments, and the most Cenococcum mycorrhizae formed in burned clearcuts. Rhizopogon species occurred in the clay-silt soil of the low-elevation site only when that soil was loosened and aerated in the soil transfer. The greatest numbers of Cenococcum mycorrhizae were found at the high-elevation site, and the greatest number of Brown mycorrhizae on the mid-elevation site. Major field mycorrhiza types iere also observed in the greenhouse. Rilizopogon and Brown types constituted the same proportion of total mycorrhizae on both greenhouse and field seedlings from sites 2 and 3, but not site 1. Greenhouse proportions of Cenococcum and other infrequent mycorrhiza types did not reflect field proportions. Seedling growth, as well as nonrnycorrhizal and total root tip numbers were increased in pasteurized soil. Reinoculation of pasteurized soils reduced nonmycorrhizal and total root tip numbers, albeit not to original levels. A reinoculation ratio of 1 (nonpasteurized soil): 9 (pasteurized soil) produced as many mycorrhizae as entirely nonpasteurized soil. For these sites, fungal propagule availability or alterations of soil biology and chemistry by timber harvest and slash burning are less important as determinants of first year mycorrhizal associations than above-ground alterations in the seedling environment. Mycorrhiza formation may be impaired by dense or clayey soils. Some soil microbiological factors limit seedling growth. Silvicultural management of the above-ground environment to ensure prompt regeneration and inoculation of nursery stock with several species of site-specific mycosymbionts snould optimize rnycorrhizal symioses of outplanted seedlings.
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