Mycorrhiza formation and diversity in undisturbed forest and clearcut and burned areas in three forest types in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3x816q04d

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  • A greenhouse bioassay was used to compare ectomycorrhiza formation and diversity in soils from undisturbed and clearcut and burned areas in moist mesic, moist montane and dry montane forest types representing a gradient of environmental harshness. It was hypothesized that mycorrhiza diversity decreases with increasing environmental harshness and that stability of mycorrhiza formation following clearcutting and burning is positively related to mycorrhiza diversity. Soils were collected from three forest/clearcut pairs in each forest type. Clearcut and burned areas were well-stocked with both planted and naturally seeded conifers. The field soils were used to inoculate greenhouse planting media in which Douglas-fir and ponderosa pine seedlings were grown. Douglas-fir seedlings were grown in moist mesic and moist montane soils and ponderosa pine seedlings were grown in dry montane soils. Numbers of mycorrhizal root tips and short roots by mycorrhiza type were determined and used to calculate percent mycorrhizal colonization, mycorrhiza type proportions, diversity indices, and branching indices. For undisturbed forest soils, percent mycorrhizal colonization and diversity index of root tips increased across the gradient from the moist mesic to the dry montane sites. Numbers of total and mycorrhizal root tips were significantly higher in undisturbed soils from the dry montane type but did not differ between undisturbed moist montane and moist mesic soils. Greater numbers of total and mycorrhizal root tips in the dry montane soils may be partially due to the tendency of ponderosa pine roots to branch more than those of Douglas-fir. Two mycorrhiza types, Rhizopogon sp. and an unidentified brown type, dominated all soils and were usually accompanied by several minor types, each of which seldom comprised more than 5% of the mycorrhizal root tips. When clearcut and burned soils were compared with undisturbed forest soils within each forest type, percent mycorrhizal colonization was higher in clearcut than in undisturbed soils from both the moist mesic and the dry montane types. Numbers of mycorrhizal root tips were higher in clearcut soils from the moist mesic and the dry montane types while numbers of total root tips were higher in clearcut soils from the dry montane type only. Mycorrhizal diversity was consistently lower in clearcut soils from all forest types but in no case was the difference in diversity between forest and clearcut significant. Type composition differed between forest and clearcut soils from the dry montane type but not from the moist mesic or the moist montane types. Mycorrhiza diversity and overall stability of mycorrhiza formation following clearcutting and burning. Mycorrhiza formation was significantly higher in clearcut than in forest soils at the sites with both the highest and lowest mycorrhiza diversity.
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