Mycorrhizal fungi have a symbiotic (mutually beneficial) relationship with many types of plants. The fungi, which are sometimes referred to as arbuscular mycorrhizal (AM) or vesicular arbuscular mycorrhizal (VAM) fungi, colonize plant roots. Together, the plant and fungi form structures, called arbuscules, on the roots. The fungi receive sugars from the plant and, in return, the fungi enhances the ability of plant roots to extract water and nutrients, particularly phosphorus.
Recently, researchers have found that plants benefit from the fungal relationship in many other ways. Scientists studied the effect of mycorrhizae on barrel medic, a relative of alfalfa. Although the fungi inhabit the roots, their effects can be found in the foliage. Plants with the fungi had higher levels of the growth hormones abscisic acid (ABA) and jasmonate. ABA improves drought tolerance by affecting the loss of water from pores (stomata) in the leaves. Jasmonate produces chemicals that protect the plant from disease and from stress in general. Plants with mycorrhizae in their roots also produced higher levels of anthocyanins and other flavonoids in their foliage; these antioxidants are responsible for colour and other plant characteristics (and may have health benefits for humans who eat the food).
In general, plants with the fungi had improved shoot growth and the capacity for greater resistance to drought, stress and disease. To protect and enhance these beneficial organisms, farmers can minimize tillage, keep the soil covered as much as possible, avoid the use of chemical fertilizers, practice crop rotation and limit applications of phosphorus fertilizers, including rock phosphate.
Source: Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula. Lisa Adolfsson, Hugues Nziengui, Ilka N Abreu, et al. Plant Physiology, 2017; Volume 175, Issue 1. pp: 392-411.
- Janet Wallace