​A Complete Guide to Mycorrhizae Fungi on Vascular Plant Roots

Food security and climate change are among the greatest challenges for humankind’s long-term survival. The unequal distribution of wealth - including food wealth - has potential for global conflict over resources.

  • Plants will continue to play an important role in managing the greenhouse effect through their photosynthetic and energy potential.
  •  Mycorrhizae fungi can help us grow healthier stronger plants.
  • Hence, they have an important contribution to make towards the more secure future for which we all long.

We aim to provide a comprehensive body of knowledge about mycorrhizal fungi in a single place. We begin by examining them in the context of the wider plant kingdom. Perhaps you are more interested in learning about their role in slowing climate change by boosting crops. In that case, you can skip the next section for now. Although you should visit it sometime to help you understand the process even better.

Let’s Start by Analysing The Different Types of Fungi

Fungi of various types are all around us.

  • They fulfill the essential role of helping trees and plants rot so the nutrients return to the soil.
  • Therefore, we could call them nature’s gardeners if we liked, helping keep our planet greener.
  • Some grow above ground, and are a pleasure to behold like these gorgeous amanita muscaria showing three stages of growth.
 Others live beneath the ground, including our main topic, mycorrhizae fungi.

Amanita Muscaria Division Basidiomycota: Onderwijsgek BY CC 3.0

Scientists used to call all types of fungus ‘plants’, because they thought they were rooted to a spot as the ones in the picture sure are Nowadays they are not so confident about their assessment, because in some cases fungi germ cells can actually swim. Now that is an intriguing thought: Fungus swimming in the bath! Let’s move to high ground and list the various types of fungus flourishing on our planet.

  • Basidiomycota mushrooms, puffballs, stinkhorns, and bracket fungi on wood. Some have such gorgeous colours they are like nature’s landscapers …
  • Blastocladiomycota fungi living in water and damp soils and digesting trash of any kind they find. So nature’s trash collectors in a way …
  • Chytridiomycota fungus eating decaying organisms including keratin in skin and hair. They clean up after so us good to have around, thanks fellas!
  • Neocallimastigomycota fungi in the digestive tracts of large, plant-eating mammals like cows and sheep. They have a useful role in fibre digestion
  • Microsporidia living in the digestive systems of people and other organisms with immune deficiency. They can cause debilitating diseases, not our friends
  • Our real friends, Glomeromycota. They have a symbiotic relationship with vascular plants and can help with climate and food security.

That was just an overview to get us closer to our main topic. We turn our attention to those mycorrhiza fungi living in a win-win relationship with vascular plants.

​A Brief Overview of Vascular Plants

We move on to discussing how Mycorrhiza Fungi enjoy a beneficial mycorrhizae relationship with higher-order plants

  • The word ‘vascular’ means having vessels or ducts carrying liquids and solvents from roots up to leaves.
  • We can compare this inversely to our own circulatory system that distributes essential elements via our blood.

 The vascular group of plants includes the following species:

  • Conifers
  • Cycads
  • Clubmosses
  • Ferns
  • Horsetails,
  • Flowering plants
  • Whisk Ferns

These wither and die when the soil dries out. Wise gardeners understand they need water at their roots, not on their leaves. To summarise briefly:

Vascular plants have water-carrying tissues enabling more vigorous growth

Vascular plants have specialized roots, stems and leaves to facilitate this.

​A Brief Introduction to Mycorrhizae Fungi

A mycorrhiza is a process, usually beneficial and between certain fungi and vascular plants occurring via their root systems. This fungi process either occurs inside or outside the plant cells, depending on the particular fungus after it colonises the roots. Essentially:

  • The plant captures solar energy through its chlorophyll and delivers it to the fungus
  • The mycorrhizae fungus delivers moisture and nutrients from the soil to the plants via the same vascular system

​Overview of the Various Mycorrhizal Fungi Types

Scientists originally classified the mycorrhizae fungi as either endotrophic (inside the root) or ectotrophic (outside the root. Nowadays they use a wider range to describe mycorrhizal types.

Arbuscular Endomycorrhizas

These are the commonest mycorrhiza type associated with 80% of plant types including many crops. Hence, they have greatest potential in our quest. The relationship occurs inside the root structure.

 Ericoid Endomycorrhizas

Ericoid Endomycorrhizas are on the outside of root structures and are less common, but better adapted to harsher environments such as moorlands. Typical mycorrhizae hosts include heathers and lings. There are two subsets to this mycorrhizal fungi category:

  • Arbutoid mycorrhiza fungi that penetrate the outer layer of root structures
  • Monotropoid endomycorrhizas that form a dense sheath around the roots

Orchidaceous Endomycorrhizas

These are similar to Ericoid Endomycorrhizas, except the nutrition they provide is more suited to orchid plants. They are common in orchid growing mediums containing coconut husk, fir bark, sphagnum moss, and tree fern fibres.

Ectotrophic Mycorrhiza Fungi

Ectotrophic fungi are the most advanced in the classification, because they penetrate through the outermost cell layers forming a net. The structure then extends out to explore soil. They can spread between trees forming the ‘wood-wide-web’ as some call it.

​How the Mutual Plant / Fungi Relationship Works

Mycorrhizae fungi are clearly beneficial to plants, because:

  • They enable essential crops like maize and wheat to grow tall
  • The process is also essential for the health of trees
  • Hence they perform an essential role in the sequestration of carbon
  • Moreover they help farmers grow more abundant crops to feed the people

Indeed, one could argue the food chain could nor develop without this natural process. Later, we examine its influence on

  • Carbon sequestion, crop yield increase
  • Reduced reliance on chemical inputs
  • The role of fungicides, do we need them
  • Water-soluble phosphorous fertiliser.

But first, let’s examine how the process works in more detail.

Mutual Exchange of Sugar-Water and Minerals

The mycorrhiza system provides a regular supply of carbohydrates as follows.

  • Glucose reaches the mycorrhizal fungi via the plant’s vascular system
  • The fungi flourish underground, despite no direct access to sunlight and air.
  • Thus the mycorrhiza fungi can absorb more water and nutrients in the soil.
  • This travels up the plant’s vascular system enhancing its health and growth.

Indeed, a plant is incapable of absorbing nutrients such as phosphate on its own. The fungi also release other nutrients locked up in decaying wood, that plants would not be able to access in the shorter term.

Mechanisms by which Mycorrhiza Fungi Increase Moisture Absorption

Specialised mycorrhizae use a combination of physical processes and chemical absorption to increase the uptake of moisture.

  • PHYSICAL

The fine filaments (mycelia) in the gungi network are smaller in diameter than even the most delicate root hairs. Hence, they are able to explore soil material that plants cannot reach, detect moisture and nutrients, and absorb them through their relatively larger surface area.

  •    CHEMICAL

The cell chemistry of the membranes of mycorrhizal fungi differs from plants.

  • Firstly, they may secrete organic acid to dissolve or combine ions.
  • Secondly, they are able to release ions from minerals by exchanging them.

These mechanisms make mycorrhiza fungus an ideal plant partner in moisture and nutrient deficient soils.

​Resistance to Disease, Salinity and Insects

Plants associated with these fungi can often shake off diseases caused by microbial germs in soil. Their defences above and belowground are stronger, because the mycorrhizal fungus excretes enzymes that nematodes and other soil organisms find poisonous.

  • Studies by Jung, Martinez-Medina, Lopez-Raez and associates report the relationship has a priming effect that acts as a primary immune response.
  • This acts as a precursor to the plant’s natural response. Hence, when an attack does come, the shields on a stronger plant are already in position.

​The Significant Contribution to Soil and Plant Heath

Arbuscular mycorrhizal fungi also correlate well with soil fertility on the biological level, relative to soil disease, bacteria, and fungi.

  • Being able to alleviate salinity has a positive effect on plant productivity.
  • Plants grow and perform better under salt stress conditions
  • Although their host fungi may grow slower as they take the strain

Johnson, David, Gilbert, and Lucy found the mycorrhiza process empowers plants to use their underground connections to send and receive warnings between other plants.

  • The host plant informs surrounding plants of an insect attack.
  • It then releases organic chemicals to attract appropriate insect predators,
  • The population of plants spread the information through the network
  • This in turn enables a coordinated counter attack on the invasion.
The climate benefits too, because their leaves remain more intact, and hence more able to recycle carbon. Research by Babikova, Zdenka, Lucy Gilbert and associates suggests the mycorrhiza fungi benefit extends to alerting fellow plants to herbivore activity.

​Plant Colonization of Barren Soil and Resistance to Toxicity

Plant colonization is the process whereby plants spread out and increase their collective productivity. This is essential for the survival of the food chain, and countering the greenhouse effect causing climate change.

  • However, sterile soil and growth media may prevent plant development without mycorrhiza fungi in attendance, to assist with uptake of nutrients via their root systems.
  • These is evidence that alien plants with this facility may slow the growth of indigenous plants without it
  • Mycorrhizal fungus proved beneficial to pine trees planted in contaminated soil. They displayed high tolerance, survivorship and growth in a study by Tam and Pail.
  • Two other studies demonstrated mitigation of the effects of zinc. This may have been the result of an exchange of ions at the mycelium level of the mycorrhiza fungus

​Plant Colonization - One of Fundamentals of Terrestrial Life

​We owe our existence to plants. After they migrated from water to land, they harvested nutrients from rocks to form original soils on which they and other life could settle.

  • Atmospheric oxygen levels steadily increased as leaves began to proliferate
  • This enticed other organisms to come onshore, and feed on the abundant food

​The ‘Colonization of the Terrestrial Environment’ Symposium

The New Phytologist Trust hosted a symposium on the Colonization of the Terrestrial Environment in July 2016.

Researchers arrived from all over the world, eager to discuss how plants colonised land and how this affected Earth’s history. They produced a report how creatures crawled onto the land to feed on the progeny of a multicellular species of green algae, the grandparent of all plant life.

  • Evolving plant life had new challenges to face after the green algae landed.
  • The sun damaged them with ultraviolet rays and threatened to dry them out.
  • Plants developed systems to carry moisture and nutrients from the soil.

The New Phytologist Trust provides a handy guide to the summary appearing here.

Atmospheric oxygen became sufficiently dense half a billion years ago, to enable mammals to develop, and migrate throughout the planet. The Colonization of the Terrestrial Environment symposium determined this was due to photosynthesis by

  • Hornworts
  • Liverworts
  • Mosses
  • Ferns
  • Lycophytes
  • Gymnosperms
  • Flowering Plants
 The symposium confirmed that these early plant forms benefited from an association with glomeromycota fungi of which the arbuscular mycorrhiza is a family member.

​Ancient Evidence of the First Beneficial Fungi

There is a 400-million year old treasure chest called the Rynie Chert in the form of an intact sedimentary deposit in Aberdeenshire, Scotland.

  • Mycorrhizae fungi are present in 92% of plants preserved in sufficient detail.
  • Arbuscular mycorrhizal fungi are the oldest and most predominant form.

Now we understand how arbuscular fungi helped kick start life, let’s turn our attention to what they could do to help feed the world, and help stop climate change in its tracks. Our far-reaching research continues as we explore these fascinating issues.

Climate Change: We Need More Plants Please, Say Scientists

Climate scientists at the Stockholm Resilience Centre published a report in the first half of August 2018, warning Earth is nearing a ‘hothouse phase’. They are concerned about what will happen if global temperatures rise more than 2% above preindustrial levels.

They present a scenario in which the natural systems that protect us from the Sun’s heat run out of control. They warn the situation will stabilize ‘in the long term’. By then, global temperatures will be 4 to 5% higher than preindustrial levels.

All the surface ice on earth, in the glaciers and on the mountaintops will have added to the sea, with their power to reflect solar energy probably lost forever. Sea levels will be 10 to 60 meters higher than today. Much of the current coastline will be uninhabitable.

​Earth’s Tipping Points that Could Plunge Us Into the Hothouse

Climate change denialists say the Stockholm Resilience Centre report is exaggerated. That may be so, but what if it is true. Perhaps we should do something about it anyway. After all, we do seem to have entered a phase of severe weather events suggesting something is not working as it should.  The Stockholm Resilience Centre suggests the following tipping points could act like a row of dominoes:

  • Permafrost thaw
  • Loss of methane hydrates from the ocean floor
  • Weakening land and ocean carbon sinks
  • Increasing bacterial respiration in the oceans
  • Amazon rainforest dieback
  • Boreal forest dieback
  • Reduction of northern hemisphere snow cover
  • Loss of Arctic summer sea ice
  • Reduction of Antarctic sea ice and polar ice sheets

This is a complex model. The scientists say part of the solutions lies in growing more trees and plants.

  • The effect should be more powerful if the healthy plants are interacting with mycorrhizal fungi as they grow, and feed the soil.
  • These simple life forms could mean so much to our survival. This is why we published this article, and this should be your main takeaway.

​The Role Mycorrhiza Fungi Could Play in Global Food Security

The U.S. Department of Agriculture published a report on the drivers of improvements in global food security on August 21, 2018. They predict global food insecurity in low and middle-income countries should fall from 21% to 10% by 2028.

  • The problem is greatest in conflict-ridden countries in Sub-Saharan Africa, compared to Asia and Latin America / Caribbean.
  • The affected people have no money for food, let alone productive agriculture. Conflicts and extended droughts have left their toll.

All Africa shared good news on 23 August 2018, concerning how Kenyan small-scale farmers are succeeding with crops of

  • Tomatoes
  • Onions
  • Hazelnuts
  • Green beans
  • Maize
  • Cabbages
  • Peppers
  • Chillies

Their success is lifting them out of poverty as they have enough left over to sell.

​The Invaluable Role Mycorrhizal Fungi are Performing

The role of mycorrhiza fungus in interaction with healthy plants comes sharply into focus when we consider what this could to Sub-Saharan Africa’s often arid and overworked soil. We need to introduce this where it is missing and educate the people about its role.

This fungus has been with us from the beginning. Yet many have neglected it, although it holds promise to alleviate these three global scourges.

  • Global warming
  • Starvation
  • Poverty

Finally, we turn our attention to becoming stewards of the resource. How can we use it best, is it sustainable, what are the threats?

​Into the Future: Where to From Here with Glomeromycota Fungi

Glomeromycota are a separate division in the Fungi Kingdom. They are relatively unique it the sense of being able to form arbuscular mycorrhizas through penetrating vascular land plant roots.

  • We find them abundantly in soils worldwide, where they form mutually beneficial relationships with vascular plants
  • Glomeromycota are also present in water where they form associations with floating plants such are water hyacinth.

However, they do face several risks. Your final takeaway from this article is to remember what these are:

​The Three Biggest Risks to the Future of Mycorrhiza Fungus

Tilling the soil for agriculture or landscaping may introduce harmful bacteria that harm the microscopic organisms making up the fungi.

Soil erosion may carry away the fungi, harming the beneficial networks that enabled the original plant colonisation.

Irreparable damage to plants due to climate change is beginning to become a disaster if we do nothing.

Mycorrhizae Fungi are almost incredibly beneficial to our environment, by improving plant health through more efficient use of soil-based nutrients. We can restore desertified and degraded land by re-injecting them. However, what will happen if the world becomes too warm for them to sustain? Could this be the final tipping point for this series of dominoes?

  • Permafrost thaw
  • Loss of methane hydrates from the ocean floor
  • Weakening land and ocean carbon sinks
  • Increasing bacterial respiration in the oceans
  • Amazon rainforest dieback
  • Boreal forest dieback
  • Reduction of northern hemisphere snow cover
  • Loss of Arctic summer sea ice
  • Reduction of Antarctic sea ice and polar ice sheets
Compare