Mycorrhizal fungi

What is mycorrhizal fungi?

Arbuscular mycorrhizal fungi form symbioses with the roots of the great majority of land plants — an association dating back to the colonisation of land by plants. The fungus penetrates root cortical cells and forms branched structures called arbuscules, across which nutrients and carbon are exchanged: the plant supplies photosynthate, the fungus supplies mineral nutrients gathered from a soil volume far larger than the roots can reach.

Charge BioBoost contains Rhizophagus irregularis (formerly Glomus intraradices) plus Glomus etunicatum, Glomus intraradices, Glomus mosseae and Glomus aggregatum. Note that the taxonomy of this group has been revised repeatedly, so older and newer names for the same organism circulate — and Rhizophagus irregularis and Glomus intraradices in that list may reflect that history rather than two distinct organisms. Worth verifying against the supplier's strain data.

What the symbiosis delivers

Phosphorus uptake is the best-established benefit. Phosphate moves very slowly in soil, so roots rapidly deplete the zone immediately around them; hyphae extend well beyond that depletion zone and effectively enlarge the absorbing surface enormously. Zinc and copper uptake benefit similarly.

Secondary effects include improved water relations and drought tolerance, better soil aggregate stability through hyphal networks and glomalin production, and some protection against root pathogens through physical occupation and induced resistance.

What does mycorrhizal fungi not do?

They do not fix nitrogen, and the nitrogen benefit is modest and indirect. They form no association with brassicas, beets or several other non-host families, so inoculating those crops is pointless — a specific and useful thing for a grower to know. High available phosphorus suppresses colonisation, because the plant has no reason to trade carbon for a service it does not need, so inoculating a high-phosphorus soil wastes the product. Tillage disrupts existing hyphal networks. And propagule viability in commercial products is variable and not always well controlled.

How do you read the label?

Propagule or spore count per unit, and the species list. As with bacterial inoculants, the number formulated is not the number that colonises, and colonisation percentage in your own crop and soil is the only figure that answers the question.