Mycorrhiza are beneficial symbioses between plant roots and certain soil fungi. They involve more than 95% of terrestrial plants (agricultural, forest and horticultural plants). Developed by plants for several millions of years, mycorrhizal associations provide better access to soil nutrients and help plants to be naturally more resistant to environmental stresses (drought, salinity, pathogen attack ...). There are several types of mycorrhiza and the most widespread is the arbuscular mycorrhiza (AM).
This symbiosis is found in approximately 80% of terrestrial plants (majority of crop plants: fruit and ornamental trees, cereals, ornamental plants, vegetables and aromatic plants). The MA is so named because the symbiotic fungus forms branched structures (arbuscules) within cells.
The formation at the same time of a network of fungal hyphae out from roots significantly changes relationship with the plant’s surrounding soil and increases tremendously its surface of exploration for soil resources: it is estimated that the volume of soil exploited by plant roots is multiplied by 1000 thanks to mycorrhiza. This allows plants to absorb optimal amount of soil nutrients (mainly nitrogen, phosphorus and trace elements) and water which improves their quality and yield.
Mycorrhiza also play a role in bio-protection against soil pathogens (nematodes, other fungi/bacterial pathogens) by reinforcing the natural defenses of plants.
Moreover, Mycorrhiza are known to stabilize soils and to increase the fixation of CO2 in the soil, and they are particularly suitable for re-vegetation of polluted areas.
In return, the plant supplies the fungus up to 20% of the sugar it produces by photosynthesis. These sugars are essential for the development, reproduction and survival of the fungus.
Schematic representation of fungal – plant exchanges (D. Redecker)
The use of mycorrhiza is a biological technology to equip plants with a more efficient root system and to increase their natural defenses: they are bio-fertilizers, bio-protectors and bio-regulators of plant development.
Farming techniques used in recent decades (employing large quantities of fertilizers and pesticides, soil compaction ...) cause a reduction or scarcity of mycorrhizal fungi in soils subjected to intensive chemical inputs and in horticultural media. The re-introduction of appropriate fungi will improve plant growth in a biological way, while significantly reducing the need of synthetic chemical fertilizers and pesticides. The exploitation of these new biological tools opens up prospects for innovation and improvement of farming systems which minimize the risk of environmental pollution (soil, water and air) and food contamination.
Mycorrhiza are key players in ecosystem services for an environmentally compatible agriculture.