We’re looking at the ancient grains and the soil that supports them. To see why the health of the latter is so important one only needs to note that although (the founder of “The Green Revolution”) Borlaug’s dwarfed wheats do show yields higher than traditional varieties, that crucially depends on them being given intensive irrigation along with high volumes of fertilisers and pesticide; the traditional varieties outperform the modern varieties in restorative and organic farming systems. These dwarfed wheats fail under the stresses of weather or environment extremes, whereas einkorn, emmer, and many other landrace breeds thrive. And in the soil, the vital importance of mycorrhizal fungi is apparent; it seems more and more likely that this is possibly the most important signifier of soil health.
The term ‘mycorrhiza’ was coined by Professor A. B. Frank in the 1880’s. He was the first person to describe the symbiotic relationship between trees and fungi, which he named ‘mykorhiza‘. The word comes from the Greek mykes and rhiza, the combination meaning ‘fungus-root’. More than 90% of all plant families studied (80% of species) in both agricultural and natural environments form mycorrhizal associations.
They work in the plant’s root zone, attaching themselves to the roots in a symbiotic relationship where the fungi pass water and nutrients to the plants while the plant in turn ‘rewards’ its fungal helpers with a hit of energy in the form of sugars. The mycorrhizal fungi can grow to create an enormous network which vastly increases the effective root area of the plant.
“Plant uptake and mycorrhizal uptake pathway. Plants can take up nutrients by transporters that are located in epidermis or root hairs (yellow symbols) or via the mycorrhizal uptake pathway that comprises the uptake of nutrients by fungal transporters in the extraradical mycelium (red or green symbols), the transport through the hyphae from the ERM to the IRM (see mycorrhizal interface), and the uptake from the mycorrhizal interface by mycorrhiza-inducible plant transporters in the periarbuscular membrane (orange symbols). Indicated by the red and green fungal structures is the colonization of one host root by multiple fungal species that can differ in their efficiency with which they are able to take up nutrients from the soil and transfer these nutrients to their host.” © Heike Bücking & Arjun Kafle, Biology & Microbiology Dept, South Dakota State University.
This also helps to ensure that pathogenic fungi — which can lead to root-rot — are fended off. Without finding themselves stressed and under attack, the root-growth speed increases and the fungi break down organic soil matter into nutrients in a form suitable for the plant to take up, all the while providing an increased area for accessing water, thereby improving drought resistance. Crucially, all these fungi can grow at water potential levels lower than those that their host plants can tolerate. The fungi remain metabolically active, and scavenging for water and nutrients in conditions where plants curl up and die. Mycorrhizal assisted plants can therefore continue to grow in conditions where non-mycorrhizal plants would perish.
They can also benefit plants by increasing their tolerance to adverse conditions. Growth by e.g. ECM pines can continue on soil with pH that is lower and in soil temperature that are higher, than non-ECM pines can withstand.
The main structural features of the five major types of mycorrhiza © Selosse & Le Tacon (1998)
Mineral nutrients inc. potassium, calcium, copper, zinc and iron are also taken up more quickly — and in greater amounts — by mycorrhizal plants. This fungal ‘sheath’ can also aid plants caught in soils with high concentrations of heavy metals. Zinc, cadmium and arsenic have all been found in high concentrations in the sheaths. The theory is that certain mycorrhizal isolates can accumulate and isolate heavy metals in the hyphae of their fungal sheaths. The metals are then unable to reach the plant tissues and the plant remains undamaged.
Ensuring the right conditions to encourage the growth of many strains of mycorrhizal fungi is all about species diversity, enabling plants to choose to use what, when and where they require, depending on their local environmental conditions. It’s a hugely dynamic system. Plants won’t enter into this relationship unless the rhizosphere (“the narrow region of soil that is directly influenced by root secretions, and associated soil microorganisms known as the root microbiome“) conditions are right, or as they are required by the plant. In addition, mycorrhizae are known to shut down if conditions change outside of their optimum ranges and different species equally have different tolerances. It’s been seen that in the longer term annual and perennial plants, they can switch symbionts during the course of the season so that different mycorrhizal species are involved during the vegetative growth stage than are needed during the plants’ generative growth phase. When flowering they may adopt a multi-species colonisation. It’s apparent that the more diverse the system, the more effective it will be, as the mycorrhizal species require “mycorrhizae helper bacteria” — termed MHB — that contain specialised enzymes that work to solubilise nutrients (something which their mycelia cannot achieve on their own) and supply these to the mycorrhizal.
I’m currently reading Michael Phillips’ “Mycorrhizal Planet“. The next piece will be on the ‘food’ needs of plants.
