In the mushroom kingdom, rules are quite different than in the world of plants and animals. The closer to the Equator, the more animal species are outnumbered by plant species; however, it is not in the tropical rainforests where one can find the greatest variety of mushrooms.
In fact, the number of mushroom species is quite meagre in the tropics. Mycologists from the University of Tartu have come to this conclusion after analysing the variety of ectomycorrhizal mushrooms in various regions of the world. These include every kind of popular edible mushroom, i.e., milk mushrooms and boletus.
Ectomycorrhiza is a coat-like cover that mushrooms entwine over the root tops 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 as they lack the power of photosynthesis.
For distinguishing separate mushroom species, mycologists look at a special region in mushrooms’ DNA that is variable enough. “It’s like every mushroom species has its own bar code”, says Leho Tedersoo, a researcher at the Botanical and Mycological Museum of the University of Tartu. He was the primary author of the relevant article that was published in Molecular Ecology journal.
Mycologists from the University of Tartu undertook expeditions to Seychelles, Madagascar, Zambia, Gambia, Benin, Ecuador, Brazil, Malaysia, China, the Russian Far East and Australia.
Data collected from all of these trips, as well as samples from mycologists from different parts of the world, constituted the foundation for a global model that the scientists are trying to use to describe differences in the variety of mycorrhiza mushrooms around the world. 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 less mushroom species living in the roots of the trees. “There are around twenty different species, but in middle latitudes we can find DNA from at least 60 different species of mushrooms from just a single sample of mould”, Tedersoo said.
Also, as he pointed out, there is another reason for 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 subtropics. For example, pines existed on the Earth at the end of the Jurassic era, during the reign of dinosaurs. Trees that offer a home to mycorrhiza mushrooms in the tropics have come into being remarkably later.
“Estonia has one of the greatest varieties of mycorrhiza mushrooms. In Finland, the variety is smaller, because there’s no oaks”, Tedersoo said. Only truffles of different kind haven’t reached Estonia because of the relatively cold climate.
Tedersoo L, Bahram M, Toots M, Diédhiou AG, Henkel TW, Kjøller R, Morris MH, Nara K, Nouhra E, Peay KG, Põlme S, Ryberg M, Smith ME, & Kõljalg U (2012). Towards global patterns in the diversity and community structure of ectomycorrhizal fungi. Molecular ecology, 21 (17), 4160-4170 PMID: 22568722