Mycorrhizae and their key ecological role in fixing atmospheric carbon

The mycorrhizae Mycorrhizae are a spectacular form of symbiosis between fungi and plant roots, as both parties benefit. The fungus provides nutrients and water to the plant, while the plant provides carbohydrates to the fungus. In addition, it is now known that mycorrhiza is found in 97% of plant species.

The doctor in biology from the University of Granada and head scientist of the Higher Council for Scientific Research, Alberto Bago explained in his presentation at the Microbioma Academy, that they are “the most impressive supraorganisms in nature. Because, in reality, the mycorrhizae are two independent organisms that at a given moment agree and live in common, but fully integrating”.

There are different types of mycorrhizae, but for agriculture the most interesting are the arbuscular ones, also known as endomycorrhizae. When studying a root in the laboratory, it is possible to observe the propagules or spores, the hyphae and the arbuscular structures, which are seen as true "little trees" occupying all that is the plant cell.

The expert doctor in this symbiosis explained that the propagules of the fungus or spores travel through the soil until they reach a root capable of colonizing. Then, with biochemical, molecular and cytological signals, it is introduced inside the root cell, forming arbuscular structures to later expand in the soil, around the root. 

In turn, the fungus is an obligate symbiont because, according to Bago, over the last 450 million years -which is the latest dating of the appearance of arbuscular mycorrhizae-, it turns out that it has been losing its identity until become absolutely dependent on the root. Another interesting fact is that the fungi of the arbuscular mycorrhiza form a monophyletic group, that is, they all come from a common ancestor but are from different species.

Among the benefits of arbuscular mycorrhiza in agriculture, we can say that they are much more efficient in the use of both nutrients and water, because it manages to achieve balance. This is so because they absorb or retain elements that are interesting for the plant as it is interested. For example, "The clearest case is that of heavy metals: the mycorrhiza gives the plant just the copper it needs, but if there is too much copper in the soil, it retains it. So, they are natural balancers. Therefore, they will clearly increase the survival and production of plants and, above all, very important in situations of environmental stress.”, assured Alberto Bago.

It is important to highlight that the mycorrhiza does not replace fertilization, but it helps the plant to defend itself against external agents, such as pathogens, improving survival and, therefore, increasing the yield of the harvest and the profitability of the inputs. Thus, in intensive agriculture and with current environmental conditions, mycorrhiza is essential to improve plant nutrition and reduce stress.

Latest scientific advances in the study of mycorrhizae

Alberto Bago predicted that one of the great advances in the study of mycorrhizae is to investigate sporulation. “There are quite important studies in progress that show that the spores are going to become the fundamental propagule of the inoculants in the future. That they are even going to surpass those that are currently on the market”.

It should also be taken into account that all the carbon involved in the symbiosis comes from atmospheric CO2. “Through photosynthesis it enters the plant that passes it on to the fungus who will export it to the soil, to the extraradical mycelium in the form of lipids. With which, we must highlight the ecological implication of mycorrhizae in the environment. In addition, they form stable soil aggregates essential for its health, aeration, and structure.

Steps to obtain a good inoculant

In order to obtain a good inoculant, the doctor indicated that a survey of the soil must first be carried out. Then establish a trap plant for the multiplication of mycorrhizae. There, the propagules or spores are isolated, which must be selected to make pure cultures of the mycorrhizae in vitro and then in the field.

Likewise, the characteristics of a good inoculant are: 

• That it has a good number of propagules and that they are viable and that they also last that way in their presentation format.
• That they do not contain other unwanted microorganisms, contaminants or other substrates that dilute the propagules of the mycorrhiza.
• Make it easy to apply without increasing costs.
• That it does not contain additives that deceive saying that it is of rapid effect. A typical mycorrhiza takes a week to two weeks to give results.

Gel inoculant: the latest on the market

The best inoculant technology available on the market so far is the gel inoculant that contains all types of propagules. It is easy to use and keeps alive all the colonizing structures of the fungus, it is perfectly diluted in the irrigation water, it contains natural biostimulant substances for mycorrhiza. It has a certificate of purity. In turn, the colonization time is reduced with respect to conventional inoculants because when they are in a gel state, the propagules are more active than if they were dry with adjuvants or dry with solid substrates. 

“When an inoculant is applied, the first thing we are going to notice is a reinvigoration of the plant, greater root development, greater and more lasting production, an advance in production, an improvement in the quality of fruits both in flavor and in postharvest; plants are more resistant to biotic and abiotic stress and, therefore, production is healthiersaid Alberto Bago.

For the use of an inoculant, the following must be taken into account:

• The plant species and variety.
• The age or size of the plant to be mycorrhized, because the dose that has to be adjusted depends on that.
• The type and level of soil fertilization. Sometimes it is not always necessary to provide a mycorrhiza.
• The fertilization and irrigation regime to be applied.
• A grace period must be taken into account and no other type of application must be made.

As Alberto Bago stated in Microbioma Academy, this impressive form of symbiosis between fungi and plants opens up a wide range of uses and applications in agriculture due to its multiple benefits such as enhancers of nutrient uptake by plants, reduces fertilization costs and chemical inputs, increases crop productivity and quality, improves soil structure, and is crucial for atmospheric carbon sequestration.

More about Alberto Bago

Alberto Bago worked at the Zaidín experimental station in Granada. Since the beginning of his scientific career in 1989, he has carried out his research on mycorrhizae, carrying out doctoral and postdoctoral fellowships in Germany, Canada, the United States and Australia. He is a pioneer in the use of in vitro culture of mycorrhiza for biochemical, physiological and molecular studies. He has more than 40 scientific publications on the subject, and is co-inventor of two CSIC patents.