Vol.3, No.4, 284-295 (2013) Open Journal of Ecology http://dx.doi.org/10.4236/oje.2013.34033 Leaf morphological variation among paper birch (Betula papyrifera Marsh.) genotypes across Canada Anjala Pyakurel*, Jian R. Wang Faculty of Natural Resources Management, Lakehead University Thunder Bay, Thunder Bay, Canada; *Corresponding Author: [email protected] Received 25 April 2013; revised 31 May 2013; accepted 8 July 2013 Copyright © 2013 Anjala Pyakurel, Jian R. Wang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT season) had large leaf width and petiole size but low leaf hairs on adaxial surface. Thus, all these Variations in leaf morphological characteristics leaf morphological features provide a basis for have been extensively studied at both inter- and the birch to reduce water loss from leaves and intraspecific levels although not explicitly on pa- balance water use efficiency in reduced precipi- per birch (Betula papyrifera Marsh). Paper birch tation. Furthermore, the leaf characteristics populations might have considerable genotypic measured may also include phenotypic plasti- and leaf morphological variations that have city of the birch as an acclimation to the environ- allowed them to inhabit wide environmental gra- ment as in the greenhouse. dients. In this study, we analyzed variations in leaf morphological characteristics in 23 paper Keywords: Morphological Variation; Leaf Size; Leaf birch populations collected across Canada and Shape; Petiole Size; Leaf Hairiness; Climatic grown in a greenhouse. Furthermore, we exa- Variables; Paper Birch mined whether the variations in leaf morpholo- gical characteristics observed were related to the 1. INTRODUCTION climate of the population’s origin. We found sig- nificant genotypic differences in all leaf morpho- Plant species inhabiting environmental gradients ex- logical characteristics (p < 0.05) measured hibit genotypic and phenotypic difference [1,2]. It has among the birch populations. Thus, we expected been suggested that plants respond to these environ- that the morphological variations in birch might mental changes by allocating biomass among several be related to natural diversity in birch popu- plant organs in order to capture optimum light, water, lations due to environmental differences at habi- nutrient and carbon dioxide, and as a strategy to maxi- tat origin. Principal component analysis (PCA) mize growth rate [3]. Thus, plant develops the ability, reduced thirteen leaf morphological variables to often referred to as phenotypic plasticity, to produce dif- five principal components (PC) explaining 84.74% ferent phenotypes as a response to abiotic stress [4]. of the total variance in the original data. PCs Therefore, the characterization of geographical pattern of morphological variation in natural plant populations accumulated with specific leaf area, petiole and suggests possible patterns of genotypic variation and leaf width were positively related to latitudinal, plastic responses to environmental gradients [5,6]. These longitudinal, and elevational gradients at the plasticity responses are expressed at different levels such population’s origin. Unpredictably, these PCs as plant morphology, anatomy, physiology and growth. were significantly negatively correlated to preci- Leaves are the important organs for plant production pitation and aridity index at the origin. Thus, we and are sensitive to the inhabiting environment [7]. Leaf analyzed if correlations within leaf morpho- morphological variations for plants growing in contras- logical characteristics had supported the birch ting habitats have long been studied in numerous species populations to acclimate and produce unpre- such as Azadirachta indica [8], Eucalyptus sideroxy-lon dictable relations with the environment of origin. [9], and Quercus rugosa [6]. There previous studies sug- Our results showed that the populations origi- gest that small leaves track air temperature closely, where- nated in limited precipitation (during growing as large leaves suffer from overheating when water is Copyright © 2013 SciRes. OPEN ACCESS A. Pyakurel, J. R. Wang / Open Journal of Ecology 3 (2013) 284-295 285 limited [9,10]. Thus, smaller leaves are often associated [9,37]. In this study, we examined if leaf morphology with habitats at higher elevation with increased tempera- varies among paper birch populations collected across ture [11] where moisture [12] and aridity index [13] are Canada and if the variation in these leaf morphological limited. Furthermore, small leaves are characterized by a characteristics is related to the latitude, longitude, eleva- decrease in specific leaf area (SLA) and an increase in tion and climates of origin. Based on geographic and leaf hairiness. It is suggested that thick (low SLA) leaves climatic differences at a population’s origin, we tested can better withstand wilting in comparison to thinner the following hypotheses: 1) leaf morphological charac- leaves in dry and hot environments [9,14]. Additionally, teristics vary among paper birch populations grown in leaf hairs can influence leaf water relations by increasing the same environment; 2) leaf morphological characteri- boundary layer resistance [15,16] and decreasing leaf stics exhibit consistent multivariate patterns related to temperature by reflecting radiation [17]. Consequently, environmental variables at a population’s origin 3) leaf increased leaf hairs in hot and arid habitats have signifi- size, maximum width and perimeter would increase in cant influence in reducing solar radiation, leaf tempera- higher precipitation and aridity index but would decrease ture and transpirational losses [18-20]. with temperature, longitude, latitude and elevation gra- Alternatively, narrower leaves are viewed as plant’s dients; 4) specific leaf area and maximum width index adaptation to dry and hot environments, while wider would increase with increasing precipitation and aridity leaves are an adjustment to wet and cold environments. It index whereas it would decrease along temperature, lon- has been established that narrower leaves, compared to gitude, latitude and elevation gradients; 5) petiole size, petiole index and aspect ratio would decrease with re- wider leaves, provide structural reinforcement to with- ducing precipitation and aridity index but would increase stand wilting in hot, sunny and dry environments [21-23]. with temperature, longitude, latitude and elevation gra- Similarly, petiole length influences leaf arrangement, dients; 6) leaf hairiness would increase with reducing affecting light interception efficiency under different cir- precipitation and aridity index and increases along tem- cumstances [24]. Previous studies have shown that peti- perature, longitude, latitude and elevation; and 7) signi- ole size increase in larger leaves along decreasing ficant positive relationships exist among leaf sizes, spe- drought gradients, which probably reflected the need for cific leaf area, petiole sizes and leaf hairiness. mechanical strengthening to support large leaves [25,26]. However, within the deciduous broadleaved trees, petiole 2. MATERIAL AND METHODS size increases with drought which may act as a mechani- cal support to promote leaf cooling [27]. 2.1. Sample Collection and Leaf The majority of studies on leaf morphological varia- Morphological Data tion in response to climatic factors have included species Seeds of 23 paper birch populations were collected inhabiting different environments. Results of these stud- from Newfoundland, Prince Edward Island, New Brun- ies showed remarkable leaf morphological variation in swick, Quebec, Ontario, Saskatchewan, and British Co- relation to their inhabiting environments [6,28-30]. For lumbia (Figure 1). The populations’ origin ranged from example, species from the genus Betula often show sig- 20 meters to 840 meters (above sea-level) elevation, 279 nificant differences in leaf morphology such as leaf size mm to 2062 mm mean annual precipitation and 0.9˚C to [31-34] and shape [31,32,34]. Most of these studies on 8.9˚C mean annual temperature (Table 1). Three birch leaf morphological response to environmental factors seedlings from each population were grown for six have either included comparative studies among multiple months (January to June 2010) in a greenhouse at Lake- species [22] or species inhabiting different locations head University. We used a pre-mixed peat moss for pot- along environmental gradient [21,22,35]. Therefore, it is ting medium and 21 - 25 cm (upper circle size) contain- important to determine whether leaf morphology differ in ers for growing. The seedlings were well watered and wide-ranging pioneer species like paper birch (Betula fertilized once a week with a regular fertilizer (N-P-K, papyrifera Marsh.) grown in a uniform environment. To 20:20:20). The containers were rearranged randomly on a our knowledge, no studies have focused on leaf morpho- weekly basis to minimize the effects of environmental logical variations of the birch populations grown in a patchiness in the greenhouse. In July 2010, we randomly uniform environment. harvested leaves from the middle crown of the popula- Paper birch (Betula papyrifera Marsh.), the most tions. Five well-developed leaves from each seedling widely distributed pioneer tree species in Canada [36], is were randomly chosen for leaf morphological