Wood Reacts to Bending

cross section of a balsam poplar tree with irregular inner rings

Biological Strategy

Balsam poplar

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Many resources that living systems require for survival and reproduction constantly change in quantity, quality, and location. The same is true of the threats that face living systems. As a result, living systems have strategies to maintain access to shifting resources and to avoid changing threats by adjusting their location or orientation. Some living systems modify their position by moving from one location to another. For those that can’t change location, such as trees, they modify position by shifting in place. An example of an organism that does both is the chameleon. This creature can move from place to place to find food or escape predators. But it also can stay in one place and rotate its eyes to provide a 360-degree view so that it can hunt without frightening its prey.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Tension wood of poplars reacts to bending stresses via a specialized gelatinous wall layer.

“Conifers and angiosperms evolved different strategies to achieve the bending of the stem with secondary growth. Both these strategies involve the formation of the reaction wood asymmetrically on one side of the stem. Conifers produce the compression wood (CW) on the side of the stem that needs to elongate more compared with the opposite side, while angiosperms produce the tension wood (TW) on the side of the stem that needs to shrink relative to the other side. In a typical TW, a specialized gelatinous (G) wall layer is formed during the final stage of fiber differentiation, partially replacing S3-, S2- and, in some species, also S1-layers. Many properties of TW and CW differ from normal wood (NW) in opposite ways. While the typical TW is less lignified, and has more longitudinally oriented microfibrils, higher cellulose crystallinity and higher cellulose content, the CW contains more lignin and has a flatter microfibril angle, less crystalline cellulose and lower cellulose content than NW (reviewed in Timmel 1986, Pilate et al. 2004). It is thought that the structural differences between the reaction wood and the wood on the opposite side (so-called opposite wood, OW) induce different residual growth stresses of both sides of the stem, resulting in a bending moment (Fournier et al. 1994, Bamber 2001, Almeras et al. 2005, Clair et al. 2006a).” (Nishikubo et al. 2007:843)

Nishikubo N, Awano T, Banasiak A, Bourquin V, Ibatullin F, Funada R, Brumer H, Teeri TT, Hayashi T, Sundberg B and others. Xyloglucan endo-transglycosylase (XET) functions in gelatinous layers of tension wood fibers in poplar – A glimpse into the mechanis

Last Updated August 18, 2016

References

Journal article

Xyloglucan endo-transglycosylase (XET) functions in gelatinous layers of tension wood fibers in poplar - A glimpse into the mechanism of the balancing act of trees

Nishikubo, N.; Awano, T.; Banasiak, A.; Bourquin, V.; Ibatullin, F.; Funada, R.; Brumer, H.; Teeri, T. T.; Hayashi, T.; Sundberg, B.; Mellerowicz, E. J.

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