The Actinorhizal Symbiosis

Alder root nodule

Much of the new nitrogen entering temperate forests comes from bacteria, classified in the genus Frankia, that live in root nodules on shrubs and trees. These root nodules, or “actinorhizal root nodules”, are the major N₂-fixing symbioses in broad areas of the world. The symbiosis has become increasingly important as climate changes threaten to remake the global landscape over the next several decades.

The Bacterial Symbiont - Frankia

Frankia with vesicles (DAPI /Sytox Green)

Frankia sp. strains are filamentous bacteria that convert atmospheric N₂ gas into ammonia. This process is known as nitrogen fixation. Frankia fix nitrogen while living in root nodules on “actinorhizal plants”.  Frankia thus can supply most or all of the host plants' nitrogen needs. Consequently, actinorhizal plants colonize and often thrive in soils that are low in combined nitrogen. The recent availability of three Frankia genomes may help clarify the evolution of prokaryote/plant symbioses, environmental and geographical adaptation, metabolic diversity and horizontal gene flow among symbiotic prokaryotes.

Actinorhizal Plants

Actinorhizal plants are a diverse group of woody species found on all continents (except Antarctica). Many are common plants, like alder, bayberry, sweet fern, etc. that one might pass every day. Others live in remote parts of the world. All play significant roles in the ecology of the soils in which they grow.

Some actinorhizal plants can be used as sources of biomass for generating energy or for carbon storage; some have been used for remediating stressed or contaminated soils; others have been used for lumber, fuelwood, for preventing erosion and as coastal windbreaks.

Actinorhizal Associated Plant

menjiplak dari : http://web.uconn.edu/mcbstaff/benson/Frankia/FrankiaHome.htm dan sumber lainnya.