Mushrooms galore in temperate climes

In the mushroom kingdom, the rules are different from those in the world of plants and animals. Animal species are outnumbered by plants the closer they are to the equator, yet the greatest variety of mushrooms is not found in the tropical rainforests, where the number of mushroom species is quite meagre.

Mycologists from Estonia’s University of Tartu reached this conclusion after analysing the variety of ectomycorrhizal mushrooms in various regions of the world. The species studied included every kind of popular edible mushroom.

The Tartu biologists undertook expeditions to the Seychelles, Madagascar, Zambia, Gambia, Benin, Ecuador, Brazil, Malaysia, China, the Russian Far East and Australia.

Data collected from the trips, as well as samples sent by mycologists from different parts of the world, constituted the foundation for a global model the scientists are trying to use to describe differences in the variety of mycorrhiza mushrooms around the world.

Ectomycorrhiza is a coat-like cover that mushrooms entwine over the roots of trees. Mushrooms decompose organic waste matter and make it easier for trees to obtain minerals from the earth. In exchange, trees provide sugars for the mushrooms – something the latter cannot produce on their own because they lack the ability to photosynthesise sunlight.

To distinguish separate mushroom species, mycologists study a special region in the DNA. “It’s like every mushroom species has its own bar code”, said Dr Leho Tedersoo, a researcher at the botanical and mycological museum at Tartu.

Tedersoo is the principal author of a paper describing the research in Molecular Ecology.

The first assumption – that there are more mushrooms in southern regions – turned out to be wrong. In tropical rainforests the circulation of matter is very rapid and rotten leaves decompose quickly, resulting in fewer mushroom species living in the roots of the trees.

“There are around 20 different species in rainforests but in the middle latitudes we can find DNA from at least 60 different species of mushrooms from just a single sample of mould,” Tedersoo said.

He explained that there was another reason for the relatively small variety of different mushrooms in the tropics.

The oldest trees, such as pines, firs and larches – the ones that live in symbiosis with mycorrhiza mushrooms – belong to the temperate zone of the northern hemisphere and sub-tropics. Pines existed on Earth at the end of the Jurassic era, during the reign of dinosaurs, but trees that offer a home to mycorrhiza mushrooms in the tropics arrived millions of years later.

“Estonia has one of the greatest varieties of mycorrhiza mushrooms. In Finland, the variety is smaller because there are no oaks,” Tedersoo said. Only truffles of different kinds have not reached Estonia because of the relatively cold climate.