6 June 2018

Peeking into the black box: discovering fungal diversity below ground

In a ground-breaking study, scientists have been able to uncover the diverse world of soil-dwelling ectomycorrhizal fungi across Europe. Discovering the influences of soil, climate, pollution and tree host has revealed some surprising results.

Fungi mushrooming near a leaf

The importance of soil, and the organisms that live within it, has been known for many years.

However, it has been impossible for scientists to disentangle this impenetrable black box due to the below ground growth of these organisms and technical difficulties. 

 

Close up of brown bumpy false truffles covered in soil
Belowground fruitbodies of false truffles (Elaphomyces granulatus) © Caroline Hobart

Now, for the first time, with scientists at Imperial College, we've been able to show the distribution, abundance and tree host preference of a major group of forest soil organisms, the ectomycorrhizal fungi across the whole of Europe.

This research investigates how the diversity and distribution of ectomycorrhizal fungi is influenced by factors including soil factors, climate, air pollution and tree host characteristics (e.g. tree species and nutrient status).

 

Microscope image of mycorrhizas
Ectomycorrhizas (outer-fungus-roots) of a false truffle (Elaphomyces sp.), Laura M. Suz © RBG Kew.

Root fungi

Ectomycorrhizal fungi are a group of organisms that have developed a mutualistic way of life.

Growing in between root cells and out of roots, they have been shown to both provide soil nutrients to trees as well as protect them from water shortages and disease, in exchange for carbohydrates from the trees.

But understanding how the fungi themselves manage to survive, how many different species there are, and where they grow, has proved elusive.

Previously, mushrooms appearing on the soil surface in autumn were the only way for mycologists to understand diversity and distribution, but we know that not all fungi reproduce above ground (e.g. truffles).

Root analysis

Now, in collaboration with one of the largest environmental monitoring networks, ICP Forests, and with support from the UK Natural Environment Research Council, we have analysed 40,000 roots from 13,000 individual soil samples across European forests.

Through the use of DNA technologies, we worked to identify the fungi that were symbiotically associated with beech, spruce, pine and oak in 137 sites.

Estimating fungal diversity across different tree species, and across different geographic zones across Europe, from southern Italy to northern Finland, and from Spain to Romania, we now have a better understanding of which mycorrhizal fungi grow where, and why.

Our research has found that environment and tree characteristics can explain mycorrhizal diversity, that the pollution thresholds used as major ecosystem assessment tools need strong downward adjustment, and that mycorrhizal specificity and plasticity have been underestimated.

Understanding distributions of these plant‐symbiotic fungi is crucial for predicting soil and forest responses to environmental change. This type of information will help us, not only to protect this important group of fungi, but also the trees that depend on them to survive.

A forest
The oak forest site sampled for the mycorrhizal survey in this study. They belong to ICP Forests, a European network of monitored sites. © Laura Martinez-Suz / RBG Kew.

References

van der Linde, S. et al (including Suz, L.M & Bidartondo, M.I.) (2018). Environment and host as large-scale controls of ectomycorrhizal fungi. Nature 558: 243–248.

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