06/07/2020
This will change the way you look at trees from now on.
We are used to their presence. We bike past them every day, we seek shelter on their shadow at the park. But we never thought they are, during all that time, communicating with each other and exchanging resources between them. There is a whole trade market under our feet, conformed by plants and fungi.
Through photosynthesis, plants are able to create sugars.
Fungi are very effective in mining mineral nutrients from the soil, like phosphorus or nitrogen.
Fungi need the sugar, and plants need the mineral nutrients. And so, at some point during their evolution, they developed an economical relationship, where they exchange those goods among each other.
The vast majority of terrestrial plant species in nature are associated in symbiosis with fungi. It's been hypothesized that these ubiquitous associations may have appeared 450 million years ago, playing a key role in the success of primitive terrestrial plants.
Plant roots are colonized by specialized fungal species, thus forming the so called mycorrhizas (Latin, from myco- ‘of fungi’ + Greek rhiza ‘root’). Mycorrhizas are the structures formed at the interface root-fungus. Mycorrhizal fungi fall in two broad categories depending on the morphology of their mycorrhizae: arbuscular endomycorrhizae fungi and ectomycorrhizae.
Hence, the plant acts as a carbon source for the fungus, which acts as an extended network beyond the depletion zone of the root. Furthermore, some mycorrhizal fungi are either strict or facultative biotrophs, which means that they obtain most or all of their carbon supplies from the host plants.
More surprising is the fact that, apparently, plants also send sugar to each other.
It has been observed that isotopically labeled carbon injected on a tree is allocated to different plants connected to the same mycorrhizal network. Most of this carbon is distributed to individuals with low carbon production, as seedlings or shaded plants. Hence, mycorrhizal networks facilitate the establishment of seedlings under stress, like drought, shading by understory growth, or limited nutrient acquisition. Every new plant on the area just “plug” itself to the network and enjoy nutrient delivery.
Several hypotheses have been proposed in order to explain the evolutionary stability of this cooperative fungal-plant mutualism. It is thought that plants and fungi keep this relationship based on mutual rewards. Is easy to imagine that at some point, one of the partners will cheat, and just take what they want from the network without contributing to it. Some plants, like orchids, are able to “hack” the network and live out it, but it is, apparently, the exception to the rule.
It has been proved that both the host plant and the fungal symbiont allocate resources preferentially to their partners depending on the resources acquired in exchange. This means that a host plant supplying more carbon to its fungal symbiont will obtain more phosphorus from this fungus than its other plant hosts, and vice versa, as this mechanism has been found to be bidirectional. As each plant and fungus on the network is linked to several partners, these many-to-many interactions are a basis for the cooperative behaviour, preventing the exploitation of the network by cheaters and increasing the fitness of all of the network participants.
A lot of questions still remain about this phenomenon, and, honestly, the more I think about it, the more intriguing and fascinating it gets.
+info https://www.nzgeo.com/stories/the-wood-wide-web/
https://www.sciencefocus.com/nature/mycorrhizal-networks-wood-wide-web/
https://www.youtube.com/watch?v=yWOqeyPIVRo
Trees talk and share resources right under our feet, using a fungal network nicknamed the Wood Wide Web. Some plants use the system to support their offsprin...
