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Mycorrhizal Fungi: Nature’s Gardeners

mycoMycorrhizae are fungi that live in a symbiotic relationship with plants in which energy and nutrient exchange benefit both organisms. The relationship results in improved survival and growth, increased rooting amidst more efficient soil structure, and bio-balance pathogens or other plant species. It is thought that as many as 90% of vascular land plants participate in such a relationship; many could not survive on their own.

Why do Mycorrhizae and Plants Co-Exist?

Mycorrhizal fungi live on the roots of the plant and either physically enter or surround the roots. Here they generate a network of filaments among multiple species of plants, soil bacteria, and other fungi. Mycorrhizae provide additional surface area for nutrient and water uptake, as much as 100 to 1,000 times. All 15 major macro and micro nutrients available in soil are absorbed and transferred to the plant.  Nitrogen and phosphorus are contributed by bacteria and shuttled to the plant through the network of filaments.

Using photosynthesis the plant then converts these building blocks into carbohydrates. This process nourishes both plant and fungi. The fungi cannot produce carbohydrates so the symbiosis is essential for survival. Nutrients are shared within the system and can be diverted to ailing members. Scientists believe that the network of mycorrhizal fungi, plants, and soil bacteria can encompass an entire forested area.

Mycorrhizal fungi also contribute protection to the plant by bio-balancing pathogens. The covering of mycorrhizal filaments acts as a physical barrier. Exudates are secreted by the fungi to bio-balance disease-causing organisms.

Why Do We Need Mycorrhizal Fungi?

A benefit of the presence of mycorrhizal fungi is increased soil porosity and improved soil structure. Tightly bound nutrients such as nitrogen, phosphorus, and iron are dissolved by enzymes the fungi release into the soil. Mycorrhizae improve soil structure in two ways. First, the fungal filaments help hold soil together.  Second, the fungi excrete glomalin, a sticky substance that binds soil together. These actions allow for increased soil porosity, aeration, water movements in addition to erosion resistance.

Many common agricultural practices have reduced or eliminated the presence of mycorrhizal fungi. Irrigation, top soil removal, tillage, erosion, road and home construction, fumigation, and the introduction of non-native plants all contribute to the loss of mycorrhizae in soil.  Commercial applications of mycorrhizae have been developed to combat the effects of today’s man-made environments featuring compacted soil, the loss of top soil, and the absence of necessary organic matter.  Botanists often amend soil with mycorrhizal fungi as it known to increase rooting generation, drought resistance, salt tolerance, crop yields, and reductions in transplant shock. Mycorrhizal plants fare better under drought conditions than plants without a fungal relationship.

Not every plant needs mycorrhizal fungi in the same way. As there are a myriad plant species so are there thousands of fungal species. Each fungus excels in its own way, be it improving soil or capturing nutrients. The dependence of the plant on mycorrhizal fungi depends on its own capabilities and environment. Some plants need a mycorrhizal relationship to survive while others merely need it during times of stress. It is clear that without the mycorrhizal relationship the Earth’s flora would be a mere whisper of its potential.

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Mycorrhizal Fungi and Their Importance to Agriculture

Introduction

A mycorrhiza mycorrhizae or mycorrhizas is a symbiotic (generally mutualistic) association between a fungus and the roots of a vascular plant. In a mycorrhizal association, the fungus colonizes the host plant’s roots, either intracellularly as in arbuscular mycorrhizal fungi (AMF), or extracellularly as in ectomycorrhizal fungi. They are an important component of soil fertility.

These are the fungi that form a symbiotic relationship with a plant forming a sheath around the root tip of the plant. The fungus then forms a Hartig Net which means that there is an inward growth of hyphae (fungal cell growth form) which penetrates the plant root structure.

The fungus gains carbon and other essential organic substances from the tree and in return helps the trees take up water, mineral salts and metabolites. Indeed, most forest trees are highly dependent on their fungal partners and in areas of poor soil, could possibly not even exist without them.

Types of Mycorrhizal fungi

Mainly two types;

  1. Ectomycorrhizas :- Hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root
  2. Endomycorrhizas :- Hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane

 

Ectomycorrhizas

Hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a hartig net of hyphae surrounding the plant cells within the root cortex. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients can be shown to move between different plants through the fungal network.

 

Funguses belong to the Basidiomycota, Ascomycota, and Zygomycota. Some Ectomycorrhizas fungi, such as many Leccinum and Suillus, are symbiotic with only one particular genus of plant, while other fungi, such as the Amanita, are generalists that form mycorrhizas with many different plants.

The fungal hyphae are extracellular between the cells of the epidermis and the root cortex. The fungal hyphae form a so-called hartig net and a fungal mantle covering the root tip. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients move between different plants through the fungal network

 

Endomycorrhizas

Hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane. Hyphae enter into the plant cells, producing structures that are either balloon-like (vesicles) or dichotomously-branching invaginations (arbuscules).

The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.

Arbuscular mycorrhizas are formed only by fungi in the division Glomeromycota. Fossil evidence and DNA sequence analysis suggest that this mutualism appeared 400-460 million years ago, when the first plants were colonizing land.

Arbuscular mycorrhizas are found in 85% of all plant families, and occur in many crop species. The hyphae of arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one of the major stores of carbon in the soil. Arbuscular mycorrhizal fungi have (possibly) been asexual for many millions of years.

Endomycorrhizas are variable and have been further classified as arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizas.
myco-cell-wall

 

 

Comparison between Ectomycorrhizas and Endomycorrhizas (Arbuscular)

myco-root

 

 

What are effects of Mycorrhizal Symbiosis on plant-soil system?

1/ Increased efficacy of nutrient acquisition, plant growth, flower formation and crop yield.
2/ Enhanced resistance to drought, environmental stress and some microbes.
3/ Reduced plant mortality after transplantation.
4/ Improved plant fitness in stressed environment.
5/ Positive effects on soil aggregation and stability and soil water retention
 

What are Advantages of Introducing Mycorrhiza?

1/ A single treatment lasts for the whole plant’s life.
2/ Reduces fertiliser use, watering costs and plantation management costs.
3/ It is compatible with commonly used herbicides and insecticides.
4/ Mycorrhizal plants exploit sources of nutrients in soils at maximum making it a sustainable approach of cultivation and production systems when using a minimum of agrochemicals.
 

What is a commercial value of established Mycorrhiza?

1/ Mycorrhizas are natural for healthy plants and are rare in disturbed, desertified and stressed environments. Thus, artificial inoculation with mycorrhizal fungi brings mycorrhiza to new planted plants and trees in such environments to help them in their establishment, growth and survival rate.
2/ A plant or tree with mycorrhiza has higher capability to survive long-term.
3/ This is a plant health insurance – one-time treatment that will grow with the plant.
 

What is erosion control mediated by functional mycorrhiza?

•  Mycelium of mycorrhizal fungi causes soil aggregation and stabilization

Reasons for reducing Mycorrhizal fungi 

•  Mycorrhizal fungi are found in undisturbed soils with other beneficial soil organisms.
•  Today’s common practices such as tillage, site preparation, road and home construction, mining and removal of topsoil can degrade the mycorrhizal forming potential of soil. The fungi improve the ability of plants to utilize the soil resources by ten to hundreds of times

 

What can we do to replenish Mycorrhizal Fungi?

Mycorrihiza is ideal for any landscape planting situation, establishment of grass seed or sod and will enhance all soil aerification practices. An extensive amount of Mycorrhizae fungi will help to promote extensive root growth, reduce heat and drought stress, improves water and nutrient uptake and can eliminate transplant shock.

The word “mycorrhizae” literally means “fungus-roots” and defines the close mutually beneficial relationship between specialized soil fungi (mycorrhizal fungi) and plant roots. About 95% of the world’s land plants form the mycorrhizal relationship in their native habitats. It is estimated that mycorrhizal fungi filaments explore hundreds to thousands more soil volume compare to roots alone.

 

Mycorrhizal Products

Benefits

•  Improves soil and plant ecosystem
•  Increases plant growth and establishment
•  Reduces transplanting stress and plant loss
•  Increases nutrient and water uptake
•  Improves soil structure and porosity
•  Reduces fertilisers