Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.).
Soolanayakanahally, R.Y., Guy, R.D., Silim, S.N., and Song, M. (2013). "Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.).", Plant, Cell & Environment, 36(1), pp. 116-127. doi : 10.1111/j.1365-3040.2012.02560.x Access to full text
Plant phenology is expected to be sensitive to climate warming. In boreal trees, spring flush is primarily temperature-driven, whereas height growth cessation and autumn leaf senescence are predominantly controlled by photoperiod. Cuttings of 525 genotypes from the full range of balsam poplar were planted into two common gardens (Vancouver and Indian Head, Canada) at similar latitudes, but with differing winter temperatures and growing seasons. There was clinal variation in spring and, particularly, summer and fall phenology. Bud flush and, despite milder climate, bud set and leaf drop were earlier at Vancouver than at Indian Head by 44, 28 and 7 days, respectively. Although newly flushed growth is insensitive to photoperiod, many genotypes at both sites became competent before the summer solstice. At Vancouver, high latitude genotypes set dormant terminal buds in mid-spring. Most other genotypes grew until mid-summer or set bud temporarily and then experienced a second flush. In both gardens and in a growth chamber experiment, earlier bud set was associated with reduced height growth and higher root-shoot ratios. Shoots attained competency ~5 weeks after flushing, which would normally prevent dormancy induction before the solstice, but may be insufficient if spring advances by more than a few weeks.
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