aktinorhizala

Actinorhizal, or aktinorhizala, refers to a functional group of dicotyledonous plants that form nitrogen-fixing root nodules through a symbiosis with the actinobacterium Frankia. This association enables the plants to extract atmospheric nitrogen and convert it into forms usable for growth, contributing to soil fertility in nutrient-poor environments.

In actinorhizal symbioses, Frankia infects the plant’s root cortex and establishes nitrogen-fixing nodules within specialized plant cells. The nodules are often determinate in development and can occur singly or in clusters along roots. The symbiosis supports plant growth in acidic, sandy, or otherwise nitrogen-deficient soils and plays a notable role in ecological succession and habitat restoration.

Representative actinorhizal genera include Alnus (alders), Casuarina and Allocasuarina (casuaras), Elaeagnus (silverberries), Myrica (bayberries), and Shepherdia (silver buffaloberries). Not all species within these families form actinorhizal nodules; the trait has evolved in multiple lineages and varies among taxa. The Frankia bacteria are free-living soil organisms that, in association with compatible hosts, enter root tissues and establish nitrogen-fixing nodules.

Ecologically, actinorhizal plants are valued for their ability to improve soil quality, aid reforestation and land rehabilitation, and provide timber or ornamental uses in some regions. The actinorhizal symbiosis is a well-studied example of plant–microbe interactions contributing to nitrogen cycling in terrestrial ecosystems.