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‘Smart’ legume decisions raise hopes for more sustainable agriculture

Pea nodule attached to a root; the pink area shows N-fixing bacteria
"Crucially, we have shown that the plant has an even finer control over its nitrogen-fixing bacterial ‘guests’ in that it can recognise if a strain is relatively better than another"

Legume plants can make ‘smart’ management decisions when it comes to interacting with their symbiotic bacterial partners to harness nitrogen from the atmosphere, a research team including a James Hutton Institute scientist has shown, offering insight into how a better understanding of these ‘smart’ interactions could help advance sustainable agriculture.

Globally, the biggest factor limiting plant growth is a lack of nitrogen. Nitrogen makes up almost 80% of the Earth’s atmosphere, but in a form that makes it unavailable to plants. However, legumes have developed a symbiotic relationship with soil bacteria which allows them to ‘fix’ nitrogen from the atmosphere into a form that plants can use, reducing the need for inorganic nitrogen fertilisers, which require huge amounts of energy to produce and lead to run-off into waterways.

Legume plants host nitrogen-fixing bacteria in specialised root growths called nodules, but these bacteria demand sugar from the plant in exchange for the nitrogen that they supply. The study, led by the University of Oxford and published in PNAS, shows that legumes can weigh up the different bacterial partners available, and then only provide sugar to the best strains, cutting off those that are less good. Thus, plants can compare different strains and invest resources accordingly.

Legumes are usually colonised by many different bacterial strains and some of these bacteria provide more nitrogen than others, creating an investment dilemma. While it was already known that some plants stop investing in bacteria which provide no nitrogen at all by cutting off their sugar supply, researchers have now discovered how legume plants make more subtle investment decisions.

Co-author Dr Euan James, of the James Hutton Institute’s Ecological Sciences department, added: “Crucially, we have shown that the plant has an even finer control over its nitrogen-fixing bacterial ‘guests’ in that it can recognise if a strain is relatively better than another.

“If a pea grower inoculates their crop with a specially selected high-performing ‘elite’ bacterial strain into a field in which the current strains are underperforming, the plant can reject these nodules in favour of supporting the nodules formed by the elite strain.

“In practical terms, the findings give us more confidence that bacterial inoculants for pea and faba bean plants will produce the same result in a real-life field setting.”

Paper: Conditional sanctioning in a legume–Rhizobium mutualism. Annet Westhoek, Laura J. Clark, Michael Culbert, Neil Dalchau, Megan Griffiths, Beatriz Jorrin, Ramakrishnan Karunakaran, Raphael Ledermann, Andrzej Tkacz, Isabel Webb, Euan K. James, Philip S. Poole, Lindsay A. Turnbull. Proceedings of the National Academy of Sciences, May 2021, 118 (19) e2025760118; DOI: 10.1073/pnas.2025760118.

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Printed from /news/%E2%80%98smart%E2%80%99-legume-decisions-raise-hopes-more-sustainable-agriculture on 19/09/21 07:00:02 AM

The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.