Stable carbon isotope composition (δ13C) was used to examine genetic and environmental variation in water-use efficiency of 11 Pinus contorta Dougl. ex Loud. populations from western Canada. Sapwood cores from 20-year-old saplings established at three sites in British Columbia, and shoots of greenhouse-grown, first-year seedlings, were analyzed. δ13C values of whole sapwood and isolated cellulose were correlated at r = 0.990 (p << 0.0001, n = 10). There were genetic differences in δ13C among populations. A population from the wet Pacific coast (P. contorta var. contorta) stood out from the others, which were all from the drier continental interior (P. contorta var. latifolia Engelm). This population had the highest indicated water-use efficiency. δ13C values of most populations increased from the wettest to the driest site with no significant change in ranking. Mean yield (stem volume) of the P. contorta var. latifolia populations was positively correlated with δ13C. Population differences at the seedling stage were not as pronounced, but δ13C values of seedling shoots and sapling wood cores were correlated. Among the 10 P. contorta var. latifolia sapling populations, δ13C decreased with an index of summer dryness and, less so, with increased elevation. It appears, therefore, that the most water-use efficient and most productive populations originate from relatively moderate, low-elevation sites with reduced likelihood of water stress.Key words: water-use efficiency, isotope discrimination, lodgepole pine, phenotypic plasticity, provenance trials.
Stable carbon isotope used to estimate water use efficiency can effectively indicate seasonal variation in leaf stoichiometry
