 Legume

A legume is a flowering plant belonging to the bean-and-pea family, Fabaceae. The word is also used for the characteristic pod-like fruit, but the plant-family meaning is intended here. Many legumes form root nodules containing rhizobia, which supply fixed nitrogen in exchange for plant-derived resources. The bacteria perform nitrogen fixation; the plant provides a regulated symbiotic setting.

A soybean experiment prevented normally cooperative rhizobia from fixing nitrogen and measured their subsequent reproductive success. The bacteria reproduced less successfully under those conditions, with observations implicating altered oxygen supply to nodules. ^[ref] This tests how resource exchange can stabilize mutualism. It does not imply that every legume forms nodules or that all partners respond identically.