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Abstract

Red spruce (Picea rubens Sarg.) and Fraser fir, [Abies fraseri (Pursh) Poir] are two species of conifer trees that dominate the mountaintop spruce-fir forests of the Southern Appalachian Mountains, USA, a community that is considered a boreal remnant of the last glacial maximum. Their persistence has been attributed, at least partially, to the frequent cloud immersion that matches the distribution pattern of these remnant boreal species. Although fundamental to photosynthetic carbon uptake and growth, little is known in general about stomatal morphology or behavior in cloud-immersed, conifer forest species, although immersion has been hypothesized as facilitating carbon dioxide uptake while reducing evaporative water loss, for an enhanced water use efficiency. It is also known that the absence of any water film formation on the leaf surface (hydrophobicity) is critical for photosynthetic gas exchange. Yet, studies have also alluded to the possible importance of water vapor in cloud-immersed species. In the present study, stomatal distribution patterns and surface water repulsion from needles at high and low elevation sites were measured and compared between the two species to evaluate the potential importance of these traits for growth in a cloud-dominated habitat. It was hypothesized that hydrophobicity and stomatal densities would increase with increasing altitude in both species in response to a greater occurrence and duration of cloud immersion. This hypothesis was not supported by data, which showed that these leaf surface features were statistically similar at both altitudes sampled. However, the data did show statistically significant differences in these characteristics among the two species at the lower elevation site, raising questions about possible functional differences.

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