Several earlier posts ^1,2,3 extolled the virtues of Vesicular Arbuscular Mycorrhizal fungi (VAM) for its role in phosphorus transport as well as sequestration of massive amounts of carbon in the durable form of glomalin. This paper illuminates the relationship of plants to VAM.

Scientists at the Boyce Thompson Institute for Plant Research at Cornell University have uncovered the genes that enable plants to interact with beneficial soil dwelling fungi and to access phosphate delivered to the roots by these fungi -- a first step, they say, toward enhancing the beneficial relationship for crop plants , while reducing fertilizer use and phosphate pollution in the environment.

Discovery of the phosphate-transport genes was announced today (July 28, 2004) by Maria Harrison, a senior scientist at the Ithaca, N.Y.-based research institute, during the American Society of Plant Biologists' annual meeting in Lake Buena Vista, Fla...

In natural ecosystems, most vascular flowering plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. These mutually beneficial associations develop in the roots, where the fungus colonizes the cortex to obtain carbon from the plant. In addition to inhabiting the root, the fungus establishes hyphal networks in the soil, via which phosphorus and other mineral nutrients are transferred to the root. Thus the symbiosis has a significant impact on plant mineral nutrition and consequently on plant health. Fossil evidence suggests that plants have been associated with AM fungi since they first colonized land and today, AM symbioses are formed by almost all vascular flowering plant species. The symbiosis is a highly compatible partnership, in which both symbionts differentiate to develop specialized symbiotic interfaces (arbuscule-cortical cell) over which phosphate is transported.

Phosphorus (as well as potassium) is considered to be immobile in soil moving principally by diffusion. Diffusion is a slow, short distance process so plants soon exhaust all nutrients in contact with their roots even though surrounding soil may have plenty. Growers apply far more phosphorus to their fields than is strictly necessary since much of it is unavailable to the plants unless the soil is well colonized by VAM. Unfortunately, tillage plays havoc with VAM and so more phosphorus is used and can leech out in heavy rain.

It's not clear what researchers will discover or how they might improve this situation but the more they know about VAM the better.