17 January 2024

Microplastics affect soil fungi according to drought conditions


The impact of microplastics on the soil fungal community is affected by soil moisture content, a German study has found

by Matteo Cavallito


Moisture levels in soil can influence the effects of microplastic pollution on fungi. This is supported by research published in the journal Environmental Microbiology. The investigation, carried out by researchers at the Freie Universität Berlin, examined soil samples mixed with the plastic fragments under different conditions and obtained different results.

When the soil is well watered, says a statement by the authors, toxic chemicals in the microplastics can be released into the soil, hindering its fungal richness. With dry soil, on the other hand, “the leaching of water-extractable chemicals is less pronounced and therefore less impactful on soil fungal structure.”

The study

“Microplastics affect soil functions depending on drought conditions. However, how their combined effect influences soil fungi and their linkages with ecosystem functions is still unknown,” the study explains. To better understand this phenomenon, the authors added microplastic fibers to a portion of soil used in a previous experiment by evaluating the effects at the level of the rhizosphere, that is, the soil depth reached by plant roots.

“We found that microplastics influenced the richness of the different functional groups and the whole fungal community, in a pattern that depended on the soil water status,” the researchers explain.

In detail, “under well-watered conditions, pathogens, saprotrophs, mutualists and the whole fungal community decreased in richness with microplastics by 47%, 33%, 45% and 40%, respectively.” At the same time, “under drought conditions, although all the fungal functional groups tended to have an opposite pattern increasing in richness with microplastics, the statistical evidence was only clear for pathogens and the whole fungal community, whose richness increased by 55% and 57%, respectively.”

The drought effect

The reduction in fungal richness under wet conditions, the researchers note, is likely related to the dispersion of toxic substances in the soil and the effects of microplastics on root quality. By contrast, the effects exerted by microplastics on certain soil properties, such as water-holding capacity, porosity or aggregation, are likely to determine the opposite result under drought conditions.

On balance, in each case, microplastics have altered the relationships between soil fungi and ecosystem functions by damaging or eliminating many of them. “Microplastics in soil alter soil fungal communities, which negatively affect soil ecosystem functions,” said Yudi M. Lozano, a researcher at the Freie Universität Berlin and co-author of the study.

Stima delle quantità annue di plastica utilizzata nei terreni agricoli mondiali divise per tipologie di prodotto. FONTE: Assessment of Agricultural plastics and their sustainability. FAO, 2021

Estimated annual amounts of plastics used in global agricultural land by product type. SOURCE: Assessment of Agricultural plastics and their sustainability. FAO, 2021

The negative impact of microplastics

The research thus provides new insights into the phenomenon of microplastic pollution in soil. This latter issue calls into question the problem of excessive use of non-biodegradable materials in agriculture. Over the years, said a California Polytechnic State University research which was released in recent months, “Application of single-use plastic in the agriculture sector has increased tremendously, covering millions of acres of land worldwide.”

The authors, in particular, pointed out that U.S. farms alone generated nearly 390 tons of plastic waste each year, “with single-use low-density polyethylene mulches used in row crops contributing a significant amount to total plastic waste.” The fragments bound to accumulate inevitably impact the environment and human health. According to the FAO, global demand for plastic films for agricultural use (greenhouses, mulch and silage) will reach 9.5 million tons in 2030. That is a 50 percent increase from 6.1 million tons in 2018.