Genetic Variance in Growth of Balsam Poplar Under 16- and 8-Hour Photosynthetic Periods
Six to seven balsam poplar (Populus balsamifera L.) clones from each of four provenances on a latitudinal transect (45° to 53° at 89° to 91°W) were grown for 78 days under 16- and 8-hour photosynthetic periods. Analysis of variance and functional growth analysis were used to evaluate genetic variation in growth and development under the two regimes. Relative Growth Rate and Unit Leaf Rate of plants growing under the 8-hour regime were, respectively, 85 and 60% of those of plants under 16-hour photosynthetic periods, while final dry weight under long periods was over twice that under short ones. Leaf Area Ratio, Specific Leaf Area, and the Leaf Area Partitioning Coefficient were all larger under 8-hour periods. During the initial 30 days of the experiment, shoot-root ratio was greater under the 8-hour regime, but there was no difference between regimes by final harvest. Provenance effects were generally small and statistically nonsignificant, while clonal variation within provenances was large. The ratio of the relative growth rate of the shoot to that of roots (i.e., the allometric constant) was negatively correlated with latitude of provenance. For. Sci. 35(4):903-919.
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