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How do nitrogen-fixing microorganisms support the nutrition of some trees?

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Tall giant sequoia trees with reddish bark and thick trunks rise closely together in a dense forest at Sequoia National Park, California. — Tree A stand of giant sequoia trees (*Sequoiadendron giganteum*) in Sequoia National Park, California.

Nitrogen-fixing microorganisms support the nutrition of certain trees through a mutualistic symbiosis that allows the plants to access essential nitrogen. While atmospheric nitrogen makes up about 80 percent of the air, it is not directly usable by plants; it must first be converted into compounds like ammonia or nitrates.123

In this relationship, specific bacteria—such as Frankia—invade the root hairs of host trees and stimulate the formation of root nodules. These nodules serve as a protected environment where the bacteria multiply and convert atmospheric nitrogen into ammonia, which the tree then utilizes for its development and growth.13

While this process is most famously associated with the pea family (legumes), similar symbiotic arrangements have evolved in various other woody species. These relationships are particularly vital in ecosystems where nitrogen is limited, such as in certain boreal evergreen forests. By hosting these microorganisms, trees gain a reliable source of nitrogen, which is a critical component of proteins and overall plant metabolism.123