Scientists may have discovered the cause of malnutrition amongst Europe’s trees. A new study has found that air and soil pollution can harm symbiotic fungi that help trees get nutrients from the soil. Researchers say their findings suggest Europe is in need of stricter pollution limits.
The study, led by Imperial College London and the Royal Botanic Gardens, Kew, was published on Wednesday in Nature.
“There is an alarming trend of tree malnutrition across Europe, which leaves forests vulnerable to pests, disease and climate change,” lead researcher Dr Martin Bidartondo, from the Department of Life Sciences at Imperial and Kew Gardens, said in a press release.
The team found that this concerning trend may be due to the loss of mycorrhizal fungi. The fungi live on tree roots and provide the trees with water and essential nutrients, including nitrogen, phosphorous and potassium. In exchange, mycorrhizae – some of which are known for forming truffles and mushrooms – receive carbon from the trees.
The study included 40,000 beech, oak, pine and spruce tree roots from 13,000 soil samples. The samples were taken from 137 different forest areas in 20 European countries over the course of ten years.
Researchers found that the quality of local air and soil has a significant impact on the mycorrhizal fungi. In addition to tree characteristics, such as species and nutrient status, the team found that local environmental conditions including soil variables and atmospheric pollution were the top indicators of the types and quantities of mycorrhizae that would be present.
Various pollutants threaten mycorrhizal fungi because they can be “outcompeted by those that are more tolerant of pollution,” according to the release.
“A major finding of the study is that European pollution limits may be set far too high,” said Bidartondo. “In North America the limits are set much lower, and we now have good evidence they should be similar in Europe. For example, current European nitrogen limits may need to be cut by half.”
The team said high levels of nitrogen – which enters soil due to agricultural runoff, industrial activities and wastewater – are particularly harmful.
“The thresholds uncovered in this study should impact how we manage our forests,” Dr Laura M Suz, mycology research leader at Kew Gardens, said in a statement. “From now on, with this wealth of new information we can take a broader view of fungi and forests across the continent, and also design new fungal monitoring systems, using this study as the first ever underground baseline to test directly for large-scale drivers of change.”
Fungi are not typically protected by conservation policies, reports BBC News, which makes it difficult to “assess which species are rare or declining.”
The scientists said they hope their results will lead to new, in-depth research examining the connections between tree growth, tree health, soil, pollution and mycorrhizae.