Fungal hyphae. Photo by J. Opiola, Wikimedia Commons
(Click on the following link to listen to an audio version of this blog …. More on Mycelia and Fungal communication
As we saw last week, the hyphae in a fungus’ mycelia communicate with each other both chemically and electrically and carry out searches for resources in a very coordinated manner. A single mycelial network can have hundreds to millions of actively growing hyphal tips, and these tips are constantly interacting with the fungus’ environment and also with each other. Some of the junctions between hyphae in these networks function like “decision gates” and open and close cell membrane and intracellular pores to alter the flow of chemical and electrical information through the system. The pathways that these mycelial hyphae form resemble computer networks or, to some, neural networks of a brain!
Attempts to use fungal networks as computers are ongoing. The “Unconventional Computing Laboratory” at the University of the West of England in Bristol, UK, founded in 2001, is leading the way into “living computer” networks. A growing set of published papers in prestigious scientific journals is documenting the development of these systems.
Further, experiments to determine if these mycelial systems can learn or retain information (i.e. form “memories”) are also ongoing in a number of laboratories around the world. The potential for emergent properties to arise from these systems, possibly all the way to intelligence and consciousness, are also being seriously discussed! It is not clear how far one can take these ideas without blurring the line between Science and Science Fiction! Are the soils beneath our feet conscious? Do the soils of a forest think?
Mycelial cord (rhizomorphs). Photo by Distant Hill Garden and Nature Trail. Flickr.
The hyphae in a mycelium can become modified for efficient transport of water or food molecules. A number of hyphae can grow together into long, hollow tubes or cables that are called “cords” or “rhizomorphs.” These rhizomorphs can transport large volumes of food or water over very long distances, and are capable of dispersing a discovered resource throughout the extended body of the fungus.
As we said last week, fungi are heterotrophs. They feed on formed organic molecules that they find in their environment. Since most of the materials that a fungus will consume are dead, fungi are often classified as “saprotrophs” or ‘decomposers.” Animals are also heterotrophs (and many animals are saprotrophic, too).
Animals ingest their food (i.e. take it into their bodies) and then digest it down to its constituent molecules which they then absorb into their body fluids and deliver to their cells. Fungi, though, have a very different method of feeding. Instead of bringing the food into their bodies, they insert their bodies into the food! When a food source is found, the hyphae grow densely around and within it. The hyphae then secrete digestive enzymes which breakdown the complex molecules of the food item into their constituent components. The fungal hyphae then absorb these products of digestion and, if necessary, transport them throughout the mycelial network.
Mycorrhiza root tips, Photo by E. Larson et al., Wikimedia Commons
Hyphae can make cell to cell connections with other hyphae. Some of these connected hyphae may be parts of the same fungal individual, and some of these connected hyphae may be from different individuals. Some of these different individuals may be the same species as our starting fungus, but some of these may also be individuals of a different species. When these connections are made, communicating chemicals and also food molecules, mineral nutrients and water may be passed from one fungal individual to another. This transport is highly controlled and represents a fascinating aspect of the intraspecific and interspecific ecology of fungi!
Fungal hyphae can also make cell to cell contact with plants. This most often happens between a soil dwelling fungus and a plant’s roots. These plant root associated fungi are called “mycorrhizal fungi.” Mycorrhizal fungi can exchange food molecules, mineral nutrients and water molecules with their associated plants. They can also exchange communication molecules.
Vesicular arbuscuar mycorrhizae. Photo by R. Rit, Wikimedia Commons
The hyphae of some of these mycorrhizal fungi can actually enter the living tissues of the plant roots and make direct contact with or even penetrate into the living cells of the root. These types of mycorrhiza are called “endomycorrhiza.” The hyphae of other mycorrhizal fungi only approach the outer edges of the plant roots and often generate complex junctioning “mantels” between the hyphae and the root. These types of mycorrhiza are called “ectomycorrhiza.”
In a forest, the trees are typically highly interconnected by mycorrhizal fungi. Nutrients from one tree can flow to another. Damage to one tree can be sensed by the other trees in the forest through the dispersion of alarm chemicals both through the air and also through the mycorrhizal network. This network has been called the “Wood-Wide-Web,” and it knits trees of all types together into a mutually beneficial, social/ecological network.
The Wood-Wide-Web is a highly controlled system. There are mechanisms controlling its exchanges that balance abundance and need into an efficiently functioning system that helps to maintain the overall health of the forest ecosystem. Some have used anthropomorphic terms to simplify this complex system of nutrient and energy flow (see Signs of Fall 10, November 21, 2019 for a discussion of this), but the reality of the physiological and ecological elegance of this system is much more compelling and much more interesting than fairy tales about trees!
Rirch forest. Photo by M. Krzyszkowski, Wikimedia Commons
Most plants rely on mycorrhizal fungi to survive. Many plants need specific species of soil fungi to make their mycorrhizal networks. The ability of certain crops to grow (or not grow) in certain fields has been often shown to be related to the type of potential mycorrhizal fungi that are present in the soil. The pattern of the recolonization of tree species following the continental retreat of the Ice Age glaciers was also influenced by the potential mycorrhizal fungi present in the freshly uncovered soils. The first tree species to recolonize these vast areas were the ones for whom the proper soil fungi were present.
Plants, in fact, may owe their very existence to fungi and the tendency of fungi to make connections with plant structures. When plants first evolved and emerged onto land (about 500 million years ago), they did not have functional roots. Instead these first-plants got water, mineral nutrients and, possibly, more from the preexisting soil fungi that fused with their tissues. Fungi, then, were the first plant roots!
(In two weeks: Truffles and lichens!)