Leaf Morphological Variation among Paper Birch (Betula papyrifera Marsh.) Genotypes across Canada

Variations in leaf morphological characteristics have been extensively studied at both interand intraspecific levels although not explicitly on paper birch (Betula papyrifera Marsh). Paper birch populations might have considerable genotypic and leaf morphological variations that have allowed them to inhabit wide environmental gradients. In this study, the authors analyzed variations in leaf morphological characteristics in 23 paper birch populations collected across Canada and grown in a greenhouse. Furthermore, they examined whether the variations in leaf morphological characteristics observed were related to the climate of the population’s origin.

The authors measured leaf size (LS), perimeter (P), blade length (BL), petiole length (PL), petiole size (PS), maximum width (MW), position of maximum width (PMW), horizontal width (HW) and vertical length (VL) of the samples. And mean annual and growing season temperature and precipitation data for population’s origin were normalized climate data from years 1971 to 2001.

The results showed there were significant genotypic differences in all leaf morphological characteristics (p < 0.05) measured among the birch populations. Thus, they expected that the morphological variations in birch might be related to natural diversity in birch populations due to environmental differences at habitat origin. Principal component analysis (PCA) reduced thirteen leaf morphological variables to five principal components (PC) explaining 84.74% of the total variance in the original data. PCs accumulated with specific leaf area, petiole and leaf width were positively related to latitudinal, longitudinal, and elevational gradients at the population’s origin. Unpredictably, these PCs were significantly negatively correlated to precipitation and aridity index at the origin. Thus, they analyzed if correlations within leaf morphological characteristics had supported the birch populations to acclimate and produce unpredictable relations with the environment of origin. The results showed that the populations originated in limited precipitation (during growing season) had large leaf width and petiole size but low leaf hairs on adaxial surface.

In conclusion, the findings raised the possibility that intraspecific variation in paper birch might evolve due to genotypic variation and environmentally induced variation in leaf morphological characteristics. Contrary to our expectations, several leaf characteristics were inversely related to environmental gradient of the birch’s origin, which makes it necessary to consider the fact that the greenhouse had different environment than the habitat the populations would normally be exposed to. Furthermore, the leaf characteristics measured may also include phenotypic plasticity of the birch as an acclimation to the environment as in the greenhouse.

Article by Anjala Pyakurel and Jian R. Wang, from Lakehead University Thunder Bay, Thunder Bay, Canada.

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Image by Nicholas A. Tonelli, from Flickr-cc.