The effect of light and nitrogen limitation on western conifers : response to Armillaria ostoyae infection

Graduation date: 1990Armillaria (Fr. ex. Fr.) is a parasite whose pathogenicity\ud and role in forest ecosystems often depends upon the\ud physiological condition of the tree. Therefore, I tested the\ud frequency and severity of Armillaria ostoyae (Romagn.) Herink\ud infection among Abies grandis (Dougl.) Lindl., Larix\ud occidentalis Nutt., Pinus contorta var. latifolia (Engelm.),\ud Pinus ponderosa (Dougl. ex. Laws.), and Pseudotsuqa menziesii\ud (Mirb.) Franco. seedlings experiencing balanced, light limited\ud and nitrogen limited conditions growing in a greenhouse.\ud Armillaria ostoyae infection rates were significantly higher\ud when seedlings were light or nitrogen limited than when light\ud and nitrogen conditions were balanced.\ud The ratio of energy required for phenol degradation to the\ud energy available from sugars (Epd:EAS) and the ratio of\ud energy required for lignin degradation to energy from available\ud sugars (Eld:Eas) in the root tissue of seedlings\ud experiencing greenhouse conditions correlated with infection\ud rates (r2=0.78) and (r2=0.68) respectively. Concentrations\ud of lignin, phenolic compounds and protein precipitable tannins\ud in secondary root tissue were lower in seedlings that\ud experienced light or nitrogen limitation than when light and\ud nitrogen conditions were balanced.\ud A field study was employed to determine the frequency of\ud A. ostoyae infection in P. menziesii growing in stands that\ud were thinned or thinned plus fertilized. Armillaria ostoyae\ud infection rates were significantly higher on P. menziesii that\ud received the thinning plus fertilization treatment than those\ud trees in stands that received the thinning treatment or the\ud untreated trees. The Epd:Eas and Eld:Eas in 0.5-3.0 cm\ud diameter roots of P. menziesii also correlated with A. ostoyae\ud infection rates of (r2=O.72) and (r2=0.68) respectively.\ud Concentrations of lignin, phenolic compounds and protein\ud precipitable tannins were lower, while the concentrations of\ud sugar, starch and cellulose were higher in tissue taken from\ud 0.5-3.0 cm diameter roots of trees in stands that received\ud thinning plus fertilization than trees in stands that were\ud thinned only or those that were left untreated.\ud Energy relationships were found to be an accurate\ud predictor of successful A. ostoyae attack on western coniferous\ud seedlings. Thermochemical calculations have seldom been\ud applied to host-pathogen relationships. Energy relationships\ud may be a new and useful concept to explain the mechanism of\ud pathogen invasion of host tissues in a wide variety of\ud environmental conditions