GardenDrumPassive plants, or pushing the boundaries?

We think of plants as passive organisms, having to take what the environment dishes up. But new research suggests plants may be much smarter and strategic.

The theory began when researchers asked the question about why plants called ‘nitrogen fixers’ – those that can absorb nitrogen (N) from the air, like Australian acacias or other legumes – grow well in some locations but not others.

We would intuitively think that a nitrogen-fixing plant would grow best in areas where there is low soil N, as it can make its own and thrive, and not so well where it is abundant. But the opposite is true. Why?

The researchers, working with Professor Lars Hedlin, discovered that in places where there is lots of soil N, like a tropical forest, the nitrogen-fixers use that adaptation to get an early competitive advantage over other plants and then turn it off whenever there is a boost in soil N levels. Nitrogen fixing uses a lot of energy and, if a plant can use that energy for other things like growing up quickly to reach a limited amount of available light, it stops fixing N. Conversely in N poor soils like arboreal forests, the nitrogen-fixers keep on making it themselves, and don’t grow as quickly.

As Professor Hedlin explains:

“Tropical nitrogen-fixing plants are smart enough to know when to use costly nitrogen fixation to compete with neighboring plants, and when to turn it off, as if they are sentient beings. Nitrogen fixers in non-tropical zones are initially super competitors but end up fueling their own demise. Because their fixation is not strategic in the long term, they spread nitrogen around to their neighbors and their neighbors overcome them.”


More at Princeton News

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