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Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.)

Soolanayakanahally, R.Y., Guy, R.D., Silim, S.N., Song, M. (2013). Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.), 36(1), 116-127. http://dx.doi.org/10.1111/j.1365-3040.2012.02560.x

Abstract

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 7d, 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 midsummer 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 ∼5weeks after flushing, which would normally prevent dormancy induction before the solstice, but may be insufficient if spring advances by more than a few weeks. We studied variation in phenology in a range-wide collection of Populus balsamifera L. (balsam poplar), an important temperate-boreal hardwood, planted into two common gardens with different climate but similar photoperiod. Early bud flush caused mid- and high-latitude genotypes to cease height growth well before the summer solstice, reducing biomass accretion and favouring root growth. Shoots became competent to respond to photoperiod ∼5 weeks after flushing, which would normally be enough to prevent premature dormancy induction in spring, but may not be if flush dates advance by a few weeks. © 2012 Blackwell Publishing Ltd.

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