VARIANCE-COMPONENTS, HERITABILITIES AND GAIN ESTIMATES FOR GROWTH CHAMBER AND FIELD PERFORMANCE OF POPULUS-TREMULOIDES - GAS-EXCHANGE PARAMETERS

Five populations of trembling aspen from Alberta, Canada were tested u nder both field (north and south, grown 2 years) and corresponding gro wth chamber (north and south, grown 12; weeks) conditions and gas exch ange traits (net assimilation (NA), stomatal conductance (Gs), photosy nthetic water use efficiency (WUE)) were measured. Differences among p opulations were not significant for most traits however clone-within-p opulation explained substantially more variation in nearly all analyse s. Plants grown in a drier potting mix showed significantly lower net assimilation in the southern chamber. By the end of the growth chamber experiment (83 days), there was a significant positive correlation be tween net assimilation and both height, and root dry weight in both ch ambers. Similar correlations were not found in the field. There was al so no relationship between the growth chamber and field performance of clones. Broad-sense clone mean heritability estimates for NA, Gs and WLTE ranged from 0.28 to 0.80, 0.73 to 0.92, and 0.44 to 0.80 respecti vely. Estimates from the field sites were much more variable and rarel y as high. Gain estimates for net assimilation in the northern chamber averaged 16% (12.6% to 17.8%) across all three test dates but were fa r more variable (5.9% to 22.4%) across dates in the southern chamber w hich averaged 11%. Overall, trembling aspen in Alberta exhibits substa ntial genetic variation at the clonal level for gas exchange traits wi th limited differentiation at the population level.