What forces enable trees to stand upright?

The bark side of the force.

What forces enable trees to stand upright?
Image: Pixabay

To develop straight, plants require a motor system that controls their stance by creating powers to counterbalance gravity. Researchers have long imagined that this motor compel was controlled just by the interior powers incited in wood.

A new study by the CNRS and Cirad suggests that bark is also involved in the generation of mechanical stresses in several tree species. To understand the role of bark, scientists grew tropical species at a tilted angle.

Detail from an anatomical cross-section of a branch of a Guiana chestnut tree (Pachira aquatica) taken from the banks of the Kourou River (French Guiana). On the left, the pith. Around it, the wood, where we can make out the vessels, which transport sap. Lastly, on the outside, the bark, with fiber trellis bundles organized in flame shapes (red), set apart by parenchyma cells (blue). Credit: Bruno Clair, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/ Université de Guyane/Université des Antilles).
Detail from an anatomical cross-section of a branch of a Guiana chestnut tree (Pachira aquatica) taken from the banks of the Kourou River (French Guiana). On the left, the pith. Around it, the wood, where we can make out the vessels, which transport sap. Lastly, on the outside, the bark, with fiber trellis bundles organized in flame shapes (red), set apart by parenchyma cells (blue). Credit: Bruno Clair, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/ Université de Guyane/Université des Antilles).

The powers that created in the stems of the young staked trees delivered a stem ebb and flow when the stakes were expelled. In specific species, when the bark of the stem was expelled, this bend was lost, which shows that the powers in charge of stem up-rightening are situated in the bark.

The system producing these powers is connected to the particular structure of the bark, where the filaments are sorted out as a trellis. At the point when the stem develops, the advancement of the layers of wood expands the circumference of the bark. The trellis structure of the filaments in the bark is with the end goal that this pressure produces powers along the stem.

Anatomical cross-section of a young Cupuaç tree (Theobroma grandiflorum), grown staked and artificially tilted. In the center, the fragile tissues of the pith. Around it, the wood, which is more developed on the upper side, and whose tissue is very rich in parenchyma and almost devoid of fibers. Lastly, on the outside, the bark, which is more developed on the upper side, with bundles of fiber trellises organized into safranin-red flames, set apart by dilated parenchyma cells (colored in Astra blue). Width: 8 mm; height: 10.3 mm. Credit: © Jonathan Prunier, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/Université de Guyane/Université des Antilles)
Anatomical cross-section of a young Cupuaç tree (Theobroma grandiflorum), grown staked and artificially tilted. In the center, the fragile tissues of the pith. Around it, the wood, which is more developed on the upper side, and whose tissue is very rich in parenchyma and almost devoid of fibers. Lastly, on the outside, the bark, which is more developed on the upper side, with bundles of fiber trellises organized into safranin-red flames, set apart by dilated parenchyma cells (colored in Astra blue). Width: 8 mm; height: 10.3 mm. Credit: © Jonathan Prunier, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/Université de Guyane/Université des Antilles)

If the stem is titled, the growth is more rapid on the upper side of the stem, leading to the generation of asymmetric forces. It is this asymmetry that allows the stem to curve upwards. In five of the nine tree species studied, the generation of forces enabling the tree to offset gravity is thus not simply due to the maturing of the walls of the wood cells, but also to the wood growth in this smartly organized trellis of fibers in the bark.

Nature has solved an infinite number of engineering problems. The need for trees to grow vertically by optimizing the organization of their tissues is today a potential source of remarkable inspiration for materials science.

Young Guiana chestnut (Pachira aquatica) tree. The tree has been titled and staked. As it has grown it has generated forces in its bark to grow upright. When the tree is released from the stake, the energy accumulated is released and causes the tree to bend. Credit: © Barbara Ghislain, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/Université de Guyane/Université des Antilles).
Young Guiana chestnut (Pachira aquatica) tree. The tree has been titled and staked. As it has grown it has generated forces in its bark to grow upright. When the tree is released from the stake, the energy accumulated is released and causes the tree to bend. Credit: © Barbara Ghislain, Ecofog laboratory (CNRS/AgroParisTech/Cirad/Inra/Université de Guyane/Université des Antilles).

The study is published in the journal New Phytologist.