A particularly beautiful boletus thrives close to a protective rock. (all pictures: Artemis Treindl/ETH Zurich)
This find marks the altitude record for
B. edulis
in the Alps. Until now, its highest recorded occurences were at 2,200 metres above sea level in Ticino and in Austria. The only place this fungus is known to grow at a higher altitude than in the Lower Engadine is in the Rocky Mountains, where porcini mushrooms have been found at elevations as high as 3,500 metres.
Moreover, it wasn’t just the altitude that made the Lower Engadine find surprising. The Motta Naluns porcini mushrooms have “hooked up” with a mycorrhizal partner not previously recorded for this species of fungus: the dwarf willow
Salix herbacea
.
Many fungi form symbiotic partnerships with plants. The fungus produces mycelium, a web of fine filaments in the soil and around the root tips of the plant. This enables it to provide water and nutrients to the plant, as well as warding off harmful fungi and soil organisms. In return, the fungus receives carbohydrates such as sugars, which the plant produces via photosynthesis.
Successful switch to a new symbiont
B. edulis
is not particularly picky when it comes to the choice of plant partners and will associate with various large deciduous and coniferous trees. However, the dwarf willow was previously not a known mycorrhizal partner for this fungus – at least, not in its core distribution range. This dwarf shrub is well adapted to the harsh mountain environment, growing horizontally underground with mostly just its leaves and blossoms visible above ground.
“It’s likely that the porcini mushrooms in Motta Naluns shifted to the dwarf willow out of lack of more suitable alternatives,” Leuchtmann says. Back in the lab, the two researchers confirmed that the host plant for the fungus was indeed the dwarf willow by analysing fungal DNA they had isolated from the dwarf willow’s root tips.
It is not clear how the fungus reached this unexpected altitude or how it managed to switch hosts. It might be that the wind carried spores from nearby colonies; alternatively, this colony might be a relic of earlier times when the timberline was much higher than it is today. In parts of the Alps, the timberline lies well below its natural height because humans have cut down forest to open up land for pasture.
B. edulis
’s ability to colonise and survive at higher altitudes may also be a result of global warming.
Treindl and Leuchtmann want to study the Lower Engadine porcini mushrooms in more detail to get to the bottom of these and other unanswered questions. They are keen to discover whether the fungus is genetically distinct from nearby
B. edulis
colonies below the timberline. The ETH researchers would like to find out how closely the different populations are related to each other and whether the DNA of these alpine porcini mushrooms has changed compared to that of their forest-dwelling relatives.
