2.3.20 (HL)—Plant nitrogen fixation

Legumes house nitrogen-fixing microbes in root nodules: bacteria receive sugars and habitat, while the plant receives fixed nitrogen compounds.

The partnership matters where usable nitrogen limits growth. The plant still obtains carbon energy through photosynthesis; bacteria provide access to atmospheric nitrogen by fixation.

Beans may grow better in nitrogen-poor soil when nodules are active, but the benefit depends on compatible microbes and conditions.

Both partners gain: sugars and shelter are exchanged for fixed nitrogen.

The plant does not fix N₂ alone; do not confuse hosting bacteria with absorbing nitrate.