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 under both field (north and south, grown 2 years) and corresponding growth chamber (north and south, grown 12; weeks) conditions and gas exchange traits (net assimilation (NA), stomatal conductance (Gs), photosynthetic water use efficiency (WUE)) were measured. Differences among populations were not significant for most traits however clone-within-population explained substantially more variation in nearly all analyses. 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 between net assimilation and both height, and root dry weight in both chambers. Similar correlations were not found in the field. There was also 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 respectively. Estimates from the field sites were much more variable and rarely 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 far more variable (5.9% to 22.4%) across dates in the southern chamber which averaged 11%. Overall, trembling aspen in Alberta exhibits substantial genetic variation at the clonal level for gas exchange traits with limited differentiation at the population level.