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Populus

Populus sp.
Populus balsamifera

Continuing the series for UBC Research Week, Connor introduces the next entry: Today we feature UBC Dept. of Forest Sciences Professor and Head, Robert D. Guy from the Faculty of Forestry. He shares with BPotD a collaborative project involving multiple labs.

Poplars Popular at UBC (an article from the Faculty of Forestry newsletter, Branchlines)

There is much interest in afforestation (PDF) as a strategy to help mitigate climate change by sequestering carbon and, ultimately, providing feedstock for renewable biofuels. These opportunities are likely to be greatest in intensively managed stands of rapidly growing trees. In Canada, there are several million hectares of marginal agricultural lands potentially available, mostly in the prairie provinces. But what’s actually available to plant? Not much it seems. Most of the available hybrid poplars currently planted in Canada are derived from species or populations adapted to relatively mild climates. While some of these "mild climate" clones are suitable to southern Ontario and southwestern British Columbia, few can survive on the prairies. There is, however, within our native forests, a tremendous untapped genetic resource, pre-adapted to the Canadian climate.

Ignoring aspens, Canada supports four of five North American poplar species. For example, balsam poplar is found in every province, from the US border to Inuvik, while black cottonwood occurs throughout British Columbia and adjacent areas of Yukon and Alberta. Appropriate selections and new hybrids could greatly increase the potential area that can be successfully planted to poplar.

Several researchers at UBC are studying genotypic variation in adaptive traits in poplar. To this end, some 750+ genotypes of balsam poplar (Populus balamifera) and black cottonwood (Populus trichocarpa), plus a wide selection of hybrids (including crosses with eastern cottonwood) are now springing up, in somewhat patchy fashion, at UBC’s Totem field (see photo). This “forest” might not last long, given the rate of campus development, but many of these genotypes grow so rapidly that if left uncontrolled there would be a continuous canopy within just a few years. Most of the clones come from two range-wide provenance collections – the BC MoF black cottonwood collection originally put together by Dr. C.C. Ying, and the new AgCanBaP balsam poplar collection compiled by scientists at the Prairie Farm Rehabilitation Administration (PFRA) Shelterbelt Centre, at Indian Head, SK. The AgCanBaP collection consists of some 15 individual clones from each of 43 populations.

So what are we doing with them at UBC? Several projects are underway or have been completed. In collaboration with Richard Pharis at the University of Calgary, Rob Guy and Shawn Mansfield (Faculty of Forestry) are investigating plant hormone profiles, fiber properties, carbon isotope composition, photosynthesis, and several other physiological parameters in black cottonwood, balsam poplar and various hybrids. This work forms the basis of thesis projects for Virginie Pointeau (Guy Lab) and Faride Unda (Mansfield Lab). In addition, Raju Soolanayakanahally (Guy lab) has been working closely with Dr. Salim Silim at the PFRA, both in Saskatchewan and at UBC, to characterize growth potential, photosynthetic rates, resource-use efficiencies and single-nucleotide polymorphism (SNP) variation in the complete AgCanBap collection. Using a subset of clones from the BCMoF collection, Hannah Buschhaus (Guy lab) recently completed her MSc thesis on variation in nitrogen isotope discrimination. Activity is not restricted to just the Faculty of Forestry. Quentin Cronk (Faculty of Land & Food Systems) and colleagues in Botany, for example, have been studying morphological variation, phenology and SNPs in the black cottonwood collection.

Physiology and other fancy stuff aside, the single most important attribute dictating the rate of biomass accretion is the length of the active growing season (i.e. the period from bud break to leaf drop). Timing of bud break in the spring is largely controlled by temperature. There is genetic variation in this trait but, in the main, when trees from different locations are planted in a common garden they generally flush out within a few days of each other. The same is generally true of cottonwoods, but a notable exception we’ve noticed at the UBC common garden is that trees from very high latitude can break bud in what we locally consider to be the depth of winter (December or January!). They also set bud several months too early (during our spring) because they are sensitive to the relatively short photoperiods encountered in Vancouver. Unlike bud break, bud set and (later) leaf drop are under tight photoperiodic control, and for these traits there are very strong latitudinal clines. In a common garden, genotypes from lower latitudes are in better synchrony with local conditions and remain active over a much greater portion of the available season, and they consequently accumulate far more biomass.

Although trees representative of northern populations generally do not grow as much as those from the south over any given summer, they can in fact possess higher photosynthetic rates. Indeed, they may also show the more rapid growth if measured over just a few weeks at the height of summer. We recently reported that light-saturated photosynthetic rates increased with latitude of origin in provenances of black cottonwood. This variation was well correlated with foliar nitrogen, stomatal conductance, and stomatal density.

The cline towards increased photosynthesis with latitude may be a generalised phenomenon among deciduous trees in North America. A similar trend is found in paper birch and Sitka alder and we see the same pattern in the AgCanBaP poplar collection. We speculate that northern provenances may have inherently high photosynthetic rates to compensate for the reduced leaf longevity associated with shorter growing seasons. Indeed, under an extended photoperiod in the greenhouse, where free growth is maintained, the fastest growing balsam poplar clones are from the far north. Clearly, the intrinsic growth rate must be assessed separately from the realized growth that occurs in a common garden. In other words, the largest individuals do not necessarily have the greatest growth potential if photoperiodic adaptation is unaccounted for. This raises the intriguing prospect of breeding trees from high latitude with trees of the same species from low latitude to combine high photosynthetic rates with a longer growing season. Using balsam poplar, such crosses have now been performed by collaborators at the PFRA and the “hybrid” progeny are undergoing assessment at Indian Head.

5 Comments

Is the greenhouse plant P. balsamifera or a hybrid? Such huge leaves!

Recently there was some substantial blowing down of plantings down here. Don't know what kinds were involved. On one site near Sylvana, WA it appeared the crop was effectively destroyed. In the midst of them a large old native black cottonwood remaining standing.

thank you for all the information
this has been a fine week
ubc has much to be proud of

"This raises the intriguing prospect of breeding trees from high latitude with trees of the same species from low latitude to combine high photosynthetic rates with a longer growing season. Using balsam poplar, such crosses have now been performed by collaborators at the PFRA and the “hybrid” progeny are undergoing assessment at Indian Head."

Sounds like the one of the results Norman Borlaug had with producing wheat that as not latitude dependent.

Amazing work by UBC.

This species however, should be limited away from urban or residential parks, for so many reasons. Including allergies from the seed pods, detritus, widow makers from the giants, destruction of green space from root systems....

I probably am alone on this view....

The tree however is greatly admired sited in the natural environment, the forests, for so many (beneficial) reasons, avian sanctuary, canopy, beauty...and many more...

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