News Environment, Forestry

In many parts of Europe, mycorrhizas, a symbiotic association between tree roots and fungi that deliver nutrients and water to trees, suffer from air pollution. This was revealed in an extensive study published recently in Nature.

“The threshold values defined for critical loads of nitrogen deposition (10–20 kg per hectare per year) seem to be too high in light of this recent study. In particular, fungi that live in symbiosis with spruce and pine suffer from high levels of nitrogen deposition”, says Päivi Merilä, senior scientist at the Natural Resources Institute Finland (Luke). Merilä is coordinating Finland’s role in a major project that is investigating fungal diversity in tree roots in Europe.

“The study showed that fungi living on tree roots react to much lower levels of nitrogen deposition than was previously believed. Northern Finland is below this limit, while southern Finland is close to it, and no declining trend was detected in nitrogen deposition during the monitoring period”, Merilä says.

Lactarius rufus, the milkcap, lives in symbiosis on the tips of spruce roots. It is one of the most common fungi in Europe and suffers from nitrogen deposition. Photograph: Taina Pennanen

A mycorrhiza is a symbiotic association between fungi and plant roots. Mycorrhizal fungi improve the delivery of nutrients and water to trees, while the trees provide the fungi with carbohydrates that they are unable to produce on their own. This is a relationship that benefits both parties: symbiosis.

“This study indicates that global warming may also deteriorate the living conditions of fungi attached to plant roots. What is more, this may have an impact on forest trees in the future”, Merilä says.

Help from an international database

The project to investigate fungal diversity in plant roots in Europe used the intensive forest monitoring plots of the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (UNECE ICP Forests), which Finland has participated in since 1995. Researchers collected nearly 40,000 fungal samples from 137 forest sites in 20 European countries. The fungal species were then identified using DNA sequencing.

Pasi Rautio, senior scientist at Luke, speaks highly of the long-term international cooperation project. Factors affecting fungi living on plant roots were analysed using material available from a shared database concerning, for example, soil properties, the deposition of air pollutants, tree nutrients and climate.

“If it was not for the UN forest health monitoring programme, which uses internationally standardised methods, this study would not have been possible”, says Rautio, who is a member of the programme’s coordinating group.