Research into the sensory and social abilities of plants and their network of relationships is at the very beginning. Yet, increasingly more evidence suggests that plants are networkers, over long distances and underground. They cooperate with the long, branching fungal filaments (hyphae) through their roots. This as of yet largely unknown world of tree roots and fungal communities in the forest is called ‘the wood wide web’ or WWW.
Viewed from above, a forest appears to be a collection of individual trees – beech, oak, spruce, or alder. Yet underground, an intricately connected, highly dynamic and complex singular whole exists. The connective network of tree roots and fungi is called mycorrhiza – which in Greek literally means fungi roots. Tree roots and fungi, including edible mushrooms like porcini, chanterelles, and boletes, connect through this vast underground system. This wood wide web of tree roots and fungi is probably much larger than the visible forest.
Most non-forest plants also build slightly different underground networks from the WWW. This mycorrhiza is not visible to us.
A mycorrhizal relationship is generally symbiotic and allows both plants and fungi to thrive. Fungal filaments provide nutrients to the plants while plants provide carbohydrates like sugar to the fungi.
Even more fascinating than their mutually beneficial relationship with fungi, plants also use the carefully nurtured underground mycorrhizal network to exchange nutrients and information with each other. Experiments by Andreas Wiemken’s research group at the University of Basel found that plants engage in active relationships with neighbouring plants through the mycorrhizal network.
During a visit, he presented a photo of two pots, each containing a millet and a flax plant. A fine mesh had been inserted down the middle of each pot, separating the two plants and preventing their roots from touching. Having equal amount of soil, both pots received equal amount of soil, both pots received equal amounts of nutrients and water. In one pot, however, the flax plant grew almost twice in size and the millet plant grew slightly larger than those in the other pot. Andres Wiemken explained that the pot with the larger plants contained mycorrhizal fungi. The fungi actually had penetrated the fine mesh with their thin filaments but were invisible to the naked eye.
The research team proved that around 80 per cent of the sugar compounds in the underground mycorrhiza was produced by the millet plant in contrast to only 20 per cent by the flax plant. Yet the flax plant received 80 per cent of the sugar compounds and other nutrients mobilized from the soil by the mycorrhiza. Andres Wiemken’s conclusion was that the millet plant is feeding the flax plant indirectly. The millet plant bears most of the burden to feed the mutually beneficial fungus network, allowing the flax to reap the lion’s share of those benefits. And the millet plant is doing all this for a plant that she is not even related to!
Andres Wiemken’s team thinks that with appropriate mixed cultures, commonplace in traditional agriculture and horticulture, plants could use the mycorrhizal network to build a dynamic underground marketplace. Depending on her specific skills and level of development, each plant releases and exchanges excess nutrients with other plants in need. Clover, for example, provides her neighbours with nitrogen she acquires thanks to her symbiotic relationship with nodule bacteria. The bacteria are able to bind nitrogen from the air and make it available to the clover. In turn, plants with long roots like alfalfa, shrubs, and trees fetch water from deep within the soil to feed the mycorrhizal network. Other plants use specific enzymes and acids to acquire phosphorus from the soil. And plants like millet can generously deliver carbohydrates to the underground marketplace through efficient photosynthesis when it is hot and dry. It’s a constant give and take. “Each plant contributes to the ‘common good’ of the mycorrhizal network, according to her unique abilities, and facilitates an easier uptake of nutrients from the soil for many different plants. We are talking about a large, connected underground community here,” says Andres Wiemken.
However, plants also compete in the mycorrhizal network. For example, marigolds (Tagetes) “sweat” toxic substances (thiophenes) from their roots, transport these toxins through the network, and impede the growth of other plants. Other plants parasitize neighbouring plants by cleverly hijacking the common network. Voyria, belonging to the Gentianaceae family growing in the tropical rain forest of French Guiana, has no green leaves and does not engage in photosynthesis. The Voyria “steals” the necessary carbohydrates from surrounding plants through the common mycorrhizal network.
Initial results also show that plants use the mycorrhizal network to share information. Tomato plants were shown to warn each other of an impending caterpillar attack through the common underground network. So this network appears to function as a sort of internet for plant communities, to an extent as of yet unimaginable!
We could say: A plant is relationship within a world of connections.
FK: Thanks to mycorrhiza our soils are healthier. Shouldn’t agriculture include these findings more prominently in future practice?
AW: “Together with several partners in India, we examined exactly that. We wanted to know if and how the addition of mycorrhizal fungi and beneficial bacteria improved crop yields. In the Gangetic Plain during the wake of the Green Revolution fifty years ago, conventional agriculture began growing wheat in monoculture during the winter, rice in the summer, and rarely any legumes. The soils were degraded and the yields low, despite continual increases of chemicals and fertilizer. Actually, this unfavourable crop rotation is still found throughout the Gangetic Plain.
For several years, our Indian partners have sown a mixture of selected mycorrhizal fungi and beneficial bacteria along with seeds. Together with the Swiss project partners from the Research Institute of Organic Agriculture (FiBL) and the University of Neuchâtel, I have followed these field trials. What an amazing effect the fungi and bacteria made! The quality of wheat has improved, and the yields have increased by 40 per cent. The soil organisms supplied more nutrients to plants and at the same time improved soil structure. The benefits for rice were less pronounced perhaps because the fungi and bacteria were not appropriate for rice.”
But haven’t farmers used such relationships between soil organisms and crops in traditional agriculture for a long time?
“Yes, during our trip through remote areas of India we came across some exciting mixed cultures. In one instance, the fields looked like canola fields from a distance, flowering in a beautiful yellow colour. As we got closer, we saw wheat plants and thought it must be a wheat field. Then between the wheat and canola plants, we discovered peas, lentils, and other legumes – all ripening at different times of the year. The women go through the field daily to harvest what is ripe – a bushel for the cow here and a bushel for the kitchen there. Vast knowledge lies in this hotchpotch of crops. These traditional agricultural systems are teeming with high biodiversity. Plants in mixed cultures are generally connected underground through a common mycorrhizal network. This network must be scientifically studied more closely as it could provide important momentum for our modern, sustainable agriculture.”
Does such a network also exist in large monocultures?
“Plants that receive their nutrients from many synthetic fertilisers do not build an underground mycorrhizal network. After all, they do not need one. It is quite possible that we have unintentionally bred plants that never need to build mycorrhizal networks. Studies show that intensively managed crops have less mycorrhizal fungi. Plowing is also a problem because it destroys the networks. If plants are to grow, they must rebuild this network first, but that requires energy. So once again we need to rethink our farming practises and look for solutions to protect the soil and its fungi and microorganisms.”
It is truly amazing what a wonderful world opens to us under our feet when we start researching the soil …
“Yes! I was always fascinated by everything that happens in the soil and the many decisions that roots must make. The more we learn with research, the more our lack of knowledge, not our knowledge, seems to increase.”
Example: The Three Sisters agriculture
Maize, beans, and pumpkins comprise a mixed culture, cherished in Central America since ancient times. Maize supplies sugar compounds and serves as the beanstalk; beans provide proteins and nitrogen; and the pumpkin, which grows in the shade of maize and beans, retains moisture and prevents erosion of the soil. This mixed culture yields more than any single plant grown in monoculture. On Wikipedia, the renowned maize researcher H. Garrison Wilkes is quoted as saying the Three Sisters of agriculture (also called milpa) is “one of the most successful human inventions ever created”.
Example: Promoting the abilities of plants
Plants are excellent networkers, but their potential is lost with industrial agriculture. For example, a maize plant grown in a monoculture is sprayed and fertilized from above and below. She stands there like an autistic person, incapable of making alliances with microorganisms, establishing a common mycorrhizal network, attracting beneficial insects with fragrances, or defending herself in any way. She has become completely dependent and addicted on chemicals. Studies show that a mycorrhizal network of plants grown in monocultures is 40 per cent smaller than one of plants grown organically. This benefit is only the beginning for organic farming and other agro-ecological systems that take advantage of the plant’s abilities. What we need are farmers who are willing to collaborate with scientists, happy to experiment, and ask questions. How can we adapt conditions for our crops that allow them to develop to their greatest potential? What mixed cultures are appropriate for us? How can we activate the immune system of a plant? How can we intensify their communication with fragrances? How can we support the construction of mycorrhizal networks? How can we offer support to the army of helpers in the root zone?