Nodulated legumes in arid and semi-arid environments: are they important?

Arid and semi-arid areas occupy an increasing fraction of the Earth's surface. Legume floras exist for most of these areas, but there is little information as to whether the plants nodulate and fix nitrogen (N) in their native habitats, although many have been used over millennia for food, forage and medicinal and other uses. This review shows that, in those arid and semi-arid areas where data are available, the ability of legumes to nodulate is a significant attribute. It examines some host genera present and, where known, the bacteria that induce nodulation in them. With some exceptions all legumes from well-studied arid areas have the potential to nodulate. Semi-arid areas vary between continents in terms of legume genera present, the probable extent of N fixation and in the endosymbionts (rhizobia) that induce nodulation in them. With climate change and an increasing world population, there is an urgent need to develop the diverse range of nodulated legumes native to dry environments. With modern methods this goal is readily achievable.