Latitudinal compensation : foliar physiology of narrowleaf cottonwoods from the full latitudinal range

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Kaluthota, Sobadini
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, c2013
For deciduous trees, the growth season becomes progressively shorter with increasing latitude or elevation. To overcome the challenge of sufficient growth and development within the limited interval, deciduous trees may have adapted with increased physiological capacity. To test this ‘latitudinal compensation’ theory, I investigated the growth, foliar morphology, and some foliar biochemical and gas exchange characteristics of narrowleaf cottonwoods originating from the full range of its distribution. This study was carried out in a common garden at the University of Lethbridge, Alberta, Canada, near the northern limit of the species’ distribution. Across 167 genotypes from 9 populations representing the full 16º latitudinal range, heights and stem diameters were associated negatively (p<0.1) with the latitude of origin, while foliar morphological characteristics of blade width and leaf mass tended to be positively associated with latitude (p<0.1), and leaf mass per area (LMA) was positively associated (p<0.05). Foliar chlorophyll (chl) and nitrogen (N) content were also significantly associated with latitude, and carbon isotope composition (δ13C) was positively correlated with chl and N. With a more intensive analysis for a subset of three populations from near the southern middle, and northern limits of the distribution, these same patterns were confirmed and additionally, stomatal ratio was higher in the leaves for the northern population. Subsequently, the light-saturated photosynthetic capacity (Amax) was higher in genotypes from the northern population. I conclude that increased foliar morphological and biochemical characteristics of narrowleaf cottonwoods contribute to increased photosynthetic capacity for northern populations, providing evidence for latitudinal compensation in a deciduous tree from the northern hemisphere.
ix, 91 leaves ; 29 cm
Cottonwood -- Alberta -- Lethbridge , Dissertations, Academic