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Apple, M. E., Lucash, M. S., Olszyk, D. M. and Tingey D. T. 1998. Morphogenesis of Douglas-fir buds is altered at elevated temperature but not at elevated CO2. Environmental and Experimental Botany 40:153-172.

Global climatic change as expressed by increased CO2 and temperature has the potential for dramatic effects on trees. To determine what its effects may be on Pacific Northwest forests, Pseudotsuga menziesii, (Douglas-fir) seedlings were grown in sun-lit controlled environment chambers at ambient or elevated (+4 C above ambient) temperature, and at ambient or elevated (+200 ppm above ambient) CO2. In 1995-96 and 1996-97, elevated CO2 had no effect on vegetative bud morphology, while the following unusual morphological characteristics were found with greater frequency at elevated temperature than at ambient: rosetted buds with reflexed and loosened outer scales, convoluted inner scales, clusters of small buds, needles elongating between scales, needle primordia with white, hyaline apical extensions, and buds with hardened scales inside of unbroken buds. Buds became rosetted in elevated temperature chambers after temperatures exceeded 40 C in July, 1996. Rosettes were induced within 48-hr in buds placed in a 40 C oven; fewer rosettes formed at 20 C. Induction was reversible in buds transferred from 40 C to 20 C, implying that rosetting is a physical rather than a growth phenomenon. It appears that rosettes form after long-term exposure to elevated temperature and after shorter periods of exposure to intense heat. Elevated temperature influences bud morphology and may therefore influence the overall branching structure of Douglas-fir seedlings.

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