Population differences in water-use effeciency for Pinus contorta dougl as indicated by stable carbon isotopic composition
Creators: name: Holowachuk, Diane L.
Publisher: name: University of British Columbia
Year: 2008

description: Stable carbon isotopic composition (8¹³C), an index of water-use efficiency (WUE), was used to test genetic and environmental responses of Pinus contorta Dougl. populations to moisture gradients. To gain insight into patterns of natural selection for high or low WUE, trends in 8¹³C were measured in genotypes from different habitats. Correlations between 8¹³C and productivity were tested. Sixteen-year-old P. contorta provenance trials at three climatically different sites in British Columbia were sampled. To determine whether early selection for WUE was possible in P. contort a, greenhouse grown seedling shoots from the same seedlots as the saplings were analyzed. Correlations among seedling 8¹³C, growth variables and yield were tested as well. A sampling technique to accurately reflect field 8¹³C was determined by assessing 8¹³C variation in foliage and wood for five open-grown P. contorta saplings at one site (Juliet Creek, latitude 121° 00' N, longitude 49° 43' W, elevation 1010-1067 m). Variation in 813C within and among trees was smaller in wood than needles. Paired north and south aspects (wood) appeared to accurately track 813C year to year variation. Therefore, field 8¹³C was determined for whole wood stem cores spanning ten years growth from the northland south sides of trees. The cores were taken at stump level to avoid missing years. Depending on the site, ten or eleven populations representing a wide range of habitats (from 49° 26' to 59° 59' N latitude and 114° 25' to 132° 58' W longitude) were sampled. There were genetic differences in 8¹³C among populations. Differences were related to provenance (habitat of origin), temperature and precipitation. A particular population from the wet, maritime Pacific coast (P. contorta var. contorta) stood out from the others, which were all from the continental interior (P. contorta var. latifolia). There were no genetic differences in plasticity among populations. Indicated relative WUE increased progressively from the wettest to the driest trial site. The magnitude and direction of this increase was similar in all populations. The relationship between 8¹³C and biomass increment in controlled environments as well as in nature, was not clear. High relative WUE was related to low or high yield, depending on the population, its growing conditions, and its physiological and morphological attributes. However, correlating mean population yield at each trial site with mean 8¹³Cshowed a positive correlation between high productivity and high WUE. To understand differences within and among populations, it was apparent that the physiological and morphological bases for high productivity must be measured. Of the seedling provenances, only the coastal one had a different relative WUE. Favorable growth conditions may have nullified expression of genetic differences. In P.contorta, it appeared that early selection for WUE may be possible. Mean isotopic compositions of saplings and greenhouse grown first year seedling shoots from the same seedlots were positively correlated.