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Trees Help Curved Stems Tend Towards Sky Print E-mail
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Written by Anna Strom   
Friday, 18 May 2012 19:06

Judith Felten aspen stemsThe cut young stem to the right has received a reinforcement of mainly cellulose to grow upwards, towards the sky, from an angle. Photo by Bio4Energy. Did you know that deciduous, or leafy, trees which stems are prevented from growing upright produce additional plant matter to help them reach towards the sky? And that scientist study this mechanism hoping to find keys to make trees produce more of the coveted tree component, used to make consumer products such as printing paper, hygiene products and biofuels?

Both were things to be learned at a Fascination of Plants’ Day, given at Umeå, Sweden, as well as in 38 other countries, as part of an initiative by the Brussels-based European Plant Science Organisation.

But first let us look at the mechanism. Say, for instance, that a seed of an aspen tree took root and started growing into a tree plant on the slope of a hill. If its roots could keep it solidly in place, and there were adequate nutrients, water and sunlight, chances are that the resulting young tree would grow its delicate stem in a U-shape, with the top striving towards the sky. It would do so by reinforcing the one side of its stem with an extra layer of cellulose.* Stressors other than gravity could cause similar reactions, according to online encyclopedias. Nevertheless stability, or rather, trying to create or to maintain it, seems to be an issue.

"Trees put a whole lot of effort into growing upward", said Emma Hörnblad who does her PhD as a student researcher at the Department of Forest Genetics and Plant Physiology at Swedish University of Agricultural Sciences (SLU) and at the Umeå Plant Science Centre (UPSC) which SLU shares with Umeå University in northern Sweden.

It should be a practical matter, really. Imagine us humans trying to resist gravity if we had to keep leaning forward, with our trunks in a 90 degree angle to the ground. When it comes to deciduous trees, strains of cellulose are a chief component responsible for "pulling stems upwards", according to an e-mail advertising wood-related activities given during the Day.
Cellulose, by the way, is a main component of wood and much coveted as a raw material used to make paper, pulp, rayon fibre and hygiene products such as tissue paper—as well as ethanol-blended biofuels.

But what does the extra cellulose mean to scientists trying to develop feedstock suitable for being turned into products? Or, more specifically, what would it mean if they could control the properties that make trees grow upwards?

Production made efficient  

"It means we could harvest less trees for the same amount" or volume of products as today, said Judith Felten, a post-doctoral researcher at SLU working in the team of Björn Sundberg, head of the Bio4Energy Feedstock Platform. "We are interested in the cellulose for the sake of making bioethanol", she added.

Felten held up two cut young stems of the same aspen seed strain, having been brought up under identical conditions in a hot house—bar from the fact that the one had been grown in a flower pot tipped at an angle, whereas the other had been allowed to grow straight up from a pot which had not been tipped. The tree plant that had had to grow from an angle was markedly thicker than its straight-growing counterpart, perhaps almost twice as thick.

"We could make ten per cent more bioethanol" from the tree plant having grown an extra layer of cellulose to overcome gravity to produce a curve in its stem, Felten estimated. It is a hypothetical issue since no one would think to make ethanol of such young trees or try to establish plantations on which trees were forced to grow up in a curve.

But if trees growing upstraight could be modified to produce more cellulose, then there might be a benefit, Felten said. This was not necessarily true of Scandinavian-type biorefinery operations which generally used just about every scrap of the biomass, bar one or two percent, she acknowledged. Aspen monoculture plantations might instead be a target.

However, she stressed that her team was conducting basic research and that, "we are still a long way away" from understanding the way in which trees can be made to produce more cellulose in a regular fashion.

*In deciduous trees this extra layer of cellulose, which is found on the side of the leaning stem closest to the ground, adds thickness to the stem compared with that of a tree of the same kind and grown in identical conditions but which has not had to face the additional challenge of having to produce a curve in its stem to grow upwards. This is according to the researchers quoted in this article.