In some soils, plants need protective friends to thrive optimally: yields can be increased by up to 40 percent by enriching the soil with mycorrhizal fungi, researchers report. The study shows that the gains are mainly due to a vaccination effect against pathogens. Treatment is therefore only worthwhile if the soil has certain diagnostic values that the team has systematically recorded. The scientists say that the results can benefit the success-oriented use of mycorrhizal preparations.
Some are their enemies – but plants also have friends among the fungi: they enter into an intimate exchange relationship with certain species – a so-called mycorrhizal symbiosis. The partners exchange nutrients via a connection between the extensive network of fungi in the soil and the plant roots. The fungus supplies the plant primarily with phosphorus from the soil and in return receives carbohydrates. However, as studies have shown, the importance of symbiosis for plants goes well beyond the supply of nutrients: their defenses are strengthened and their fungal friends suppress the spread of pathogens in the soil.
Agricultural potential explored
Studies have already shown that promoting symbiosis can have a positive effect on plant growth under certain circumstances. Now, for the first time, a Swiss research team has explored on a large scale the extent to which the application of fungal spore preparations in agriculture could be worthwhile. To do this, the scientists treated 800 test areas in 54 corn fields in northern and eastern Switzerland with breeding material from a mycorrhizal fungus. The preparation was previously produced using intensively populated plants in greenhouses and incorporated into the soil before sowing. Later, the corn yields were compared between the experimental areas and the untreated controls.
The evaluations showed: “The mycorrhizal fungi enabled up to 40 percent better yields on a quarter of the fields. “That’s enormous,” says co-author Marcel van der Heijden from the University of Zurich. At first, the team could not explain the significant differences in success. The researchers found that the treatment did not lead to any increase in yield in a third of the fields. It was obvious that certain soil parameters were responsible for this enormous variance. Therefore, as part of the study, the researchers analyzed the various chemical, physical and biological soil properties of the respective test fields.
Protection against pathogens is crucial
It turned out that the positive effect of improved mycorrhization is less due to an improved nutrient supply to the plants. The researchers explain that agricultural areas are often already saturated with phosphorus. However, the yield-increasing effect occurred in the biologically weakened soils: “It became apparent that the treatment works particularly well when there are many fungal pathogens in the soil. The mycorrhizal fungi then apparently act as a kind of protective shield against these pathogens, which would weaken the plants,” says first author Stefanie Lutz from the Agroscope research institute in Zurich. The treatment is therefore not worth it on fields that are less polluted. “The plants there are already strong and growing excellently. Spreading mycorrhiza no longer brings any additional benefit here,” says co-author Natacha Bodenhausen from the Research Institute for Organic Agriculture in Frick.
According to the scientists, the importance of their study results now also lies in being able to predict which fields a mycorrhiza treatment might be worthwhile: “With certain soil indicators – mainly the presence of certain fungi – we were able to correctly confirm the success of a vaccination in nine out of ten fields “We can predict crop yields even before the field season,” says co-author Klaus Schläppi from the University of Basel. “This predictability could now make it possible to use the mycorrhiza treatment specifically in fields where it has a positive effect. “This will be crucial for this technology to develop into a reliable agricultural method,” said the scientist.
The team will now continue to dedicate itself to this goal. Van der Heijden concludes: “The results of our field trials are a big step towards more sustainable agriculture.”
Source: University of Zurich, specialist article: Nature Microbiology, doi: 10.1038/s41564-023-01520-w