Graduate Thesis Or Dissertation

 

Effects of lime and VA-Mycorrhiza interactions on growth responses of sweetgum seedlings Public Deposited

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  • A study, consisting of two sequential greenhouse experiments, was designed to determine the effects of soil liming upon the fungal partner in a mycorrhizal association. A Willamette Valley foothill soil, of the Jory series, was limed in increments to achieve a range of acidity and alkalinity. The P-deficiency and P-fixing capacity of this soil, and its strong acidity (pH 5 in 2:1 water:soil suspension) provided stressed conditions favoring mycorrhizal benefit. Two vesicular-arbuscular mycorrhizal (VAM) fungal species, Glomus fasciculatum and Glomus mosseae, were introduced into separate soil treatments and compared with non-inoculated control treatments. Stem heights, stem diameters, and leaf numbers of sweetgum (Liquidambar styraciflua L.) seedlings were measured monthly throughout the study, along with periodic monitoring of soil pH, soil nutrient levels, and VAM colonization of the roots. The experimental variable involving soil pH, mycorrhizal species, and their interactions exhibited significant effects on seedling growth. Growth of non-mycorrhizal seedlings remained minimal throughout the growing season, and appeared independent of lime applications. The efficiency of the fungal symbionts in stimulating growth was influenced by their adaptability, or tolerance, to different soil pH environments. In this study, G. fasciculatum was more efficient in acid to neutral pH conditions, and generally tolerated a wider pH range than G. mosseae. Comparatively, G. mosseae proved more efficient in neutral to alkaline pH conditions and showed less tolerance to acid conditions. The percentage colonization of sweetgum roots by the VAM fungal species corresponded to their respective enhancements of growth. However, G. mosseae exhibited a lower per cent colonization than G. fasciculatum at any pH regardless of any larger growth responses which it induced. At unlimed (pH 5) levels, there was no seedling response to G. mosseae although there was root colonization. Most nutrient concentrations in leaf tissue were little affected by lime applications; some were more affected by VAM colonization. Plant levels of Al, Fe, and Mn were noticeably influenced by both lime applications and VAM colonization. Total nutrient uptake and assimilation was substantially greater in all VAM seedlings because of their larger biomass. If maximum benefit from a mycorrhizal association is to be achieved, careful consideration should be given to employing fungal species tolerant of particular soil pH regimes.
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