Geographic variation in ecophysiological traits of black cottonwood (Populus trichocarpa)This article is one of a selection of papers published in the Special Issue on Poplar Research in Canada.

Abstract

Variation in traits related to photosynthesis and water-use were examined within and between geographic sources (provenances) of black cottonwood in two range-wide common garden experiments in British Columbia, Canada. In the first experiment, CO2 assimilation (A), stomatal conductance (gs), instantaneous intrinsic water use efficiency (WUEi), stomatal density, specific leaf area, growth height, and foliar N were measured on five 2-year-old trees of 20 clones from five widely separated provenances (i.e., 4 clones per source). Leaf disks were analysed for stable carbon isotope composition (d 13 C) to provide a more long-term measure of WUE. Photosynthetic rate per unit leaf nitrogen was used as a measure of nitrogen use efficiency (NUE). A differed between (p < 0.001), but not within provenances, and increased with latitude of origin (R 2 = 0.70). NUE and WUEi also varied between (p = 0.034 and p = 0.039, respectively), but not within provenances. In contrast, no variation among provenances was detected for d 13 C, but there were strong differences between clones within provenances (p < 0.001). Variation in A was well correlated with foliar nitrogen, g s , and stomatal density and adaxial:abaxial distribution ratio; hence, WUEi, d 13 C and NUE were mostly unrelated to latitude or associated climate variables. Species-wide patterns in stomatal density and distribution were confirmed in the second experiment which utilized 140 clones. Stomatal density on the adaxial (but not the abaxial) leaf surface was strongly correlated with latitude (p <0.001). We speculate that northern provenances may have inherently higher A and g s to compensate for shorter growing seasons.

Comparative resource-use efficiencies and growth ofPopulus trichocarpaandPopulus balsamiferaunder glasshouse conditions

“…2C) suggests variations in WUE were caused primarily by variations in stomatal conductance, which in turn reflected differences in D s . This is consistent with some previous work done on poplars (Monclus et al 2006;Gornall and Guy 2007). , only the Gillam provenance has a significant correlation between ␦ 13 C and A (r = 0.730, P = 0.017).…”

“…High WUE results either from decreased stomatal conductance, which may decrease A and therefore growth, or from increased photosynthetic capacity (Gornall and Guy 2007;Condon et al 2002). Highly significant correlation between ␦ 13 C and g s across populations (Fig.…”

“…Epidermal impressions were taken from each leaf used in gas exchange during the third measurement period following Gornall and Guy (2007). Stomatal counts for each leaf were done on three separate areas along the impression, then averaged, for both abaxial and adaxial sides of the leaf, for all genotypes.…”

“…Previous work on P. trichocarpa × Populus deltoides Marsh. (Bunn et al 2004), P. deltoides × Populus nigra L. (Monclus et al 2005), and P. trichocarpa (Dunlap et al 1993;Gornall and Guy 2007) suggests that variation in WUE is not clearly associated with variation in either conductance or photosynthetic capacity, although others have found positive correlation between growth and WUE in poplar species (Voltas et al 2006;Zhang et al 2004), indicating the possibility of generating lines with high WUE, at no cost to growth. Guy and Holowachuk (2001) suggest that high sink demand resulting from increased growth leads to an increase in photosynthetic rate and, subsequently, more positive ␦ 13 C values and higher WUE.…”

Trees of the people: the growing science of poplars in Canada and worldwideThis commentary is one of a selection of papers published in the Special Issue on Poplar Research in Canada.

“…DesRochers et al (2007) examine the interplay between water limitation, pH, and nitrogen availability, contrasting responses of a native balsam poplar to responses of fast-growing, artificial hybrid poplars. Gornall and Guy (2007) demonstrate differences in photosynthesis, nitrogen, and water relations in black cottonwoods originating from different latitudes, providing insight into how these trees are adapted to the shorter growing seasons of northern regions. These ecophysiological studies, combined with the analyses of natural aspen and cottonwood forests, demonstrate the enormous diversity across the different poplar populations, species, and hybrids.…”