Population differences in stable carbon isotope ratio of Pinus contorta Dougl. ex Loud.: relationship to environment, climate of origin, and growth potential

Stable carbon isotope composition (delta C-13) was used to examine genetic and environmental variation in water-use efficiency of 11 Pinus contorta Do ugl. ex Loud. populations from western Canada. Sapwood cores from 20-year-o ld saplings established at three sites in British Columbia, and shoots of g reenhouse-grown, first-year seedlings, were analyzed. delta C-13 values of whole sapwood and isolated cellulose were correlated at r = 0.990 (p < < 0. 0001, n = 10). There were genetic differences in delta C-13 among populatio ns. A population from the wet Pacific coast (P. contorta var. contorta) sto od out from the others, which were all from the drier continental interior (P. contorta var. latifolia Engelm). This population had the highest indica ted water-use efficiency. delta C-13 values of most populations increased f rom the wettest to the driest site with no significant change in ranking. M ean yield (stem volume) of the P. contorta var. latifolia populations was p ositively correlated with delta C-13. Population differences at the seedlin g stage were not as pronounced, but delta C-13 values of seedling shoots an d sapling wood cores were correlated. Among the 10 P. contorta var. latifol ia sapling populations, delta C-13 decreased with an index of summer drynes s and, less so, with increased elevation. It appears, therefore, that the m ost water-use efficient and most productive populations originate from rela tively moderate, low-elevation sites with reduced likelihood of water stres s.