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Efficiency prevails - why wattles rule

31 March 2016
Plant study has implications for global carbon models

Research led by the University of Sydney has revealed a group of woody plants that include Australia's iconic wattle tree behave differently to other plants. 

The results – published today in the Proceedings of National Academy of Sciences USA – also call into question the way the world models plants' carbon absorption.  

So-called woody legumes (of which acacia are the best local known example) are dominant species in many of the tropical forests the world relies on for carbon sequestration. Some current global models predicting tropical forests' uptake of carbon presume causal relationships between plant leaf nitrogen and their capacity to fix carbon.  But findings led by researchers from the University's Centre for Carbon, Water and Food demonstrate that woody legumes' ability to fix carbon from the atmosphere is unrelated to the nitrogen content of their leaves. In this regard they are unlike most other plants.

Lead researcher and director of the Centre Professor Mark Adams says the findings based on analysis of woody legumes across the globe have several implications: "First, if the relationship between leaf nitrogen and carbon fixation is less robust than previously thought, as our research suggests, the world's carbon models may need adjusting." 

As the researchers note in their article, legumes consistently maintain greater concentrations of nitrogen in their leaves compared to non-legumes, but that does not automatically translate into faster rates of carbon fixation. 

There is a now obvious need to better understand how climate and soil conditions regulate carbon fixation by woody legumes
Professor Mark Adams

Swainsona formosa, known as Sturt's Desert Pea, from north-western Australia

"Secondly, there has never been a fully satisfactory explanation as to why woody legumes dominate so much of the world's arid and semi-arid areas. This research helps fill the gap. Woody legumes' ability to conserve water while still fixing carbon put them at a distinct advantage to other plants. It's a classic case of survival of the fittest," Professor Adams said.

The researchers are now further investigating how other attributes of woody legumes, leaf chemistry for example, can be harnessed to better manage Australia and the world's carbon budgets.

"There may be scope to develop new industrial uses for native plants," Professor Adams concludes.

Legumes are different; Leaf nitrogen, photosynthesis, and water use efficiency was published on 31st March 2016. The article was a collaboration between Professor Adams and Dr Tarryn Turnbull at the University of Sydney, Professor Janet Sprent from the University of Dundee, and Professor Nina Buchmann from ETH Zurich. 

Vivienne Reiner

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