Station 6 | Root nodules of different plant families

A glance below the ground – root nodules of different plant families

Root nodules on legumes – lucerne (Medicago sativa) as an example

Lucerne or alfalfa (Medicago sativa) is a protein-rich forage plant from the legume family.

Like other legumes, lucerne can supply itself with nitrogen through a symbiosis with nodulating bacteria of the genus Rhizobium, so that fertilization is not necessary. The symbiosis occurs in small nodules formed on the plant roots. In exchange for the ammonium, the bacteria receive sugar which the plant obtains through photosynthesis. Nitrogen fixation by symbiotic nodule bacteria is used in agriculture to enrich soils with nitrogen and improve yields by ploughing in lucerne as green manure.

Root nodules on actinorhizae plants – false hemp (Datisca cannabina) as an example

While the legumes, which belong to the Fabales, can form a symbiosis for nitrogen fixation with bacteria of the genus Rhizobium, plants of three other orders (Fagales, Rosales and Cucurbitales) engage in root nodule symbiosis with bacteria of the genus Frankia. These plants are known as actinorhizae plants.

False hemp (Datisca cannabina), a herbaceous perennial, also belongs to the actinorhizae plants and can form nodules on its roots. Although the root nodules of leguminous plants and those of actinorhizae plants fulfil the same function, they often differ from each other anatomically and physically.

Header: Lucerne. Grafik: BotMuc/Tanja Simon