Soil fungi help plants take up phosphorus, but pesticides destroy the symbiosis

26. 07. 2022

Large amounts of pesticides in agricultural production can negatively affect mycorrhizal fungi, invisible to the naked eye, and thus the ubiquitous cooperation between plants and soil micro-organisms. This is suggested by the results of a unique giant survey of more than 200 soil areas from Spain to Sweden. Among the experts, who examined how mycorrhizal fungi influence the transport of phosphorus from soil to plants, were also scientists from the Institute of Microbiology of the CAS.

They have accompanied plants since 500 million years ago on their journey from aquatic environments to land. Even today, arbuscular mycorrhizal fungi coexist with more than 70% of all plant species on the planet, including the vast majority of agricultural crops and forage plants. They colonise plant roots as well as the surrounding soil, thus directly linking these two environments and replacing some root functions such as mineral nutrient uptake. These are mainly low soluble elements, of which phosphorus is the most important.

"Although we have recently learned crucial information about the occurrence of various mycorrhizal fungi on different continents and in different ecosystems, mainly thanks to increasingly sophisticated and cheaper sequencing technologies, this information does not go hand in hand with a much slower understanding of how these fungi actually function in their ecosystems," says Jan Jansa of the Institute of Microbiology of the CAS.

The functioning of the symbiosis between mycorrhizal fungi and the roots of higher plants is determined by a number of interacting factors, such as soil properties, climatic conditions and farming practices. In order to obtain reliable data, manipulative experiments and isotope methods, large numbers of soil samples and additional information on soil properties and soil management history must be used.

Giant research across Europe

Different fungi differ in their functions, as was demonstrated by previous highly simplified laboratory studies. Scientists have now set out to determine how useful naturally occurring mycorrhizal fungi are to their host plants in different field soils.

In the just-published research, the experts studied more than 200 soil areas, each representing a single agricultural ecosystem on a pan-European transect from Spain to Sweden, covering a total length of about 3,000 km. All soils were subjected to a standardised bioassay to determine the efficiency of mycorrhizal phosphorus uptake by the plant.

Acidic soil and pesticides affect phosphorus uptake

The results showed that mycorrhizal fungi collected from grassland ecosystems provided phosphorus to the plant more efficiently than those collected from fields. Quite surprisingly, however, the most important environmental factors affecting the functioning of the mycorrhizal symbiosis were different in grassland and field ecosystems. While soil acidity dominated in grassland ecosystems (the more alkaline, the more efficient mycorrhizal transfer of phosphorus from soil to plants), in field ecosystems the frequency of pesticide application dominated (the more pesticides, the less important the mycorrhizal symbiosis was on phosphorus uptake by the plant).

"Our results therefore suggest that high frequency of pesticide application in agricultural production can significantly and negatively affect the ubiquitous, albeit invisible to the naked eye, biological cooperations between plants and microorganisms below the soil surface," explains Jan Jansa.

"Such cooperations have been established over millions of years of evolution and still play an invaluable, and often underappreciated, role in the mineral nutrition of most plants."

The full potential of the symbiosis between mycorrhizal fungi and plants has not yet been fully used in today's highly productive agricultural ecosystems. On the contrary, humans have already managed, albeit unwittingly, to damage it to some extent.

This fact may yet play an important role in the future. Non-renewable natural resources, such as natural gas or phosphate ore, are technologically absolutely irreplaceable for the current way of producing food. Their availability and price may limit agricultural production in the very near future. And it may then be necessary to return to the roots and their companions, whose cooperation made natural ecosystems work long before man began to exploit them for himself.

Soil fungi help plants take up phosphorus, but pesticides destroy the symbiosis

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