Two beings that everything seems to oppose. One known for its elegance, the delicacy of its flowers exposed in greenhouses, admired in the meadows, the other populates the humus, the rotting stumps, the dark undergrowth. The hidden life of mushrooms, the mycelium, reveals an unexpected intimacy, a close link between orchids and the fungal world.
Seeds on a drip
From its first moments of life, the orchid calls for help. After flowering, a plant produces millions of seeds, so tiny and light that the wind carries them away, spreading them everywhere. Deposited on a poor meadow soil, in a swamp, wedged in a nook of branch, the future orchid is so reduced that she has no food reserves to develop any root, the smallest cotyledon. There comes the fungus. Not the porcini with its appetizing dark hat, but the mycelium, the hidden vegetative part of the fungal world. Made up of fine filaments, a tenth of a hair at most, this mycelium surrounds the seed, enters its cells in small platoons, and provides it with carbon, nutrients, water. The orchid awakens, from seed it becomes proto-form, says mycoheterotrophic because depending on the fungus, then the plant flourishes, turns green, produces its own carbon and becomes autotrophe. And can, in turn, feed the fungus.
Varied partners throughout their lives
The orchid begins its life under fungal assistance. And does not hesitate to keep the link longer, his partner with long mycelial filaments prospecting and providing him with water, nutrients, and a little extra sugar. Various mushrooms can intervene, with varied dietary patterns. Feeding on dead organic matter, parasitizing plants or establishing symbiosis, they associate with orchids. The genre Rhizoctonia is the best known of them, but the families of Tulasnellaceae and Ceratobasidiaceae are not to be outdone. Studies in tropical regions in South Africa have shown the role of Pézizes, species close to rust. In this relationship becoming lasting, the partners’ life cycles sometimes overlap one on the other, an annual fungus associating with an annual orchid, the perennials with the perennials. These associations are generally based on reciprocal exchanges, typically in symbiosis. However, sometimes the orchid benefits a little …
Les ponts mycorhiziens
It has been shown in Orchidaceae mutual exchange practices typical of symbiosis. The genres Goodyera, Serapias, offer sugars with mushrooms, and receive water and mineral elements. But other orchids have very different strategies to simplify their lives. Neottia, Corallorhiza, have a confusing behavior. These undergrowth species never turn green, devoid of leaves, chlorophyll. Their associated fungi are themselves connected to host trees, with which they develop a symbiosis. The sugars produced by the chlorophyll plant nourish the fungus, and it has been shown that the same sugars reach the orchid. The fungus becomes a delivery transporter. Water, minerals, sugars, circulate in the mycelial network. The mycorrhizae interconnect the plants between them, the mycorrhizal bridges allow a hitherto unsuspected distribution of the resources of the territory. The needs are provided in full for the orchids without leaves, and become a precious contribution for others, Epipactis, Limodorum, thus completing their insufficient photosynthetic production.
The orchid and the mushroom, in their hidden links invisible to the naked eye, reveal an unsuspected, complex organization of ecosystems. Mycorrhizae are observed on many plants, how far do they intervene in the adaptation of plants to difficult environments, too dry, too dark, too poor? How far will discoveries on mushrooms and their mycelial networks go, supports for cooperation, mutual aid, competition?