The king of the boletes, Boletus edulis is admired all over the world. Anytime a single species has more than three common names, you can bet your bottom dollar that people love and respect that species. These common names include the penny bun, and cep, but in my Sicilian family, we always called this choice edible the porcini. People for thousands of years have enjoyed collecting and consuming this species. In Latin, edulis means "eatable" or "edible." I hold these eatable porcini mushrooms near and dear to my heart as they were always an exciting a treat. We all knew that if my dad brought home a bag of dried porcinis, a heaping plate of creamy mushroom risotto was on the horizon. The intense flavor is imbedded in my memory forever.
As I became interested in mycology, porcinis were one of the first species I researched. I needed to know more about this species so nostalgic to my youth. I quickly learned that Boletus edulis is a mycorrhizal species. It tends to form symbiotic relationships with conifers like pine, spruce, hemlock and fir, but also partners well with hardwoods like chestnut, chinquapin, beech, and oak. With this broad range of potential hosts, Boletus edulis has an extensive distribution in the Northern hemisphere.
Even with its wide range of potential tree hosts, Boletus edulis is becoming rarer throughout Europe. And overharvesting is not the culprit. Unlike many sought after wild plants like Amercian ginseng that have been widely reduced by overharvesting, the porcini’s reduction is largely due to other indirect human interactions. In February of this year, Olaya Mediavilla and her team wanted to better understand the decline of this fantastic species.
In many Mediterranean ecosystems, drought is becoming more common as the global mean temperature rises. With less available water, fires are occurring not only more often, but also with greater intensity. Drawing an immediate conclusion however is ill advised as species interactions are almost always more complicated.
In recent years, the recognition of bacterial interactions has exponentially grown in the field of mycology. Bacteria are proving to be a fundamental part of the fruiting of certain species of fungi. More than two years ago I wrote an article about how specific Morchella species actually farm bacteria. Now, we have yet another example of this bacterial importance.
Mediavilla et al. 2019 found that fire disturbance altered the bacterial community. The soil bacterial community was more resilient than they predicted, but even slight changes can result in huge differences in mushroom formation. The species diversity as well as the ecological diversity of these bacterial communities is staggering! Some endobacteria actually live inside fungal hyphae and aid in the transport and synthesis of resources shared with their plant counterpart. Other free-living bacteria in the rhizosphere promote fungal growth, compete for space with pathogens, and are biochemically imperative for the synthesis of some complex compounds fungi and/or plants need. An intensely comprehensive review about bacterial-fungal interactions in the rhizosphere by Paola Bonfante and Iulia-Andra Anca can be found here.
Besides changing bacterial assemblages beneath the forest floor, changing fire regimes are changing the aboveground plant communities. In areas experiencing intense fires, plants associated with Boletus edulis are knocked back. With less carbohydrates being sent to the infamous mushroom, their energy demands are not met, and these robust organisms cannot fruit.
Our dependence on fossil fuels over the past hundred or so years has proven to have a wide variety of environmental perturbations. Intense, regular fires in Mediterranean ecosystems are not only changing belowground bacterial assemblages, but also plant productivity. The alteration of both symbiotes in this tripartite relationship has decimated our beloved porcinis. As a kid, I never would have thought that the abundance of one of my favorite foods would actually indicate our negative impact on the planet.