Mushroom Of The Week: Mushroom in a Drought?


IT'S NOT A VERY GLAMOROUS world out there in fungi-land these days due to our prolonged drought.  The fungi that are symbiotic with plants and trees, called “mycorrhizal fungi”, are still busy as bees in the soil, but they are smart enough not to try to produce any fruiting bodies, what we call mushrooms, lest they become instantly dry as toast and fail to mature and produce spores.  

Fungi are not stupid after all.  

Fungi are still alive and active helping the trees survive the drought due to their vast network of threadlike hyphae, called “mycelia,” which can extract what moisture is buried in the soil and deliver it to the tree roots in exchange for the sugars the trees produce.  

It is not an exaggeration to say that fungi are the primary way that forests survive droughts and over 90 percent of all flora have fungal partners.  Many trees, such as all pines, could not grow at all unless they had a fungal partner already in the soil.  With all this sunlight, the trees are having no problem producing sugars to share with the buried fungi, and of course oxygen for everyone else.  Up to about 80 percent of the water trees receive is due to fungi and the trees share about 30 percent of the sugars they produce in exchange for it.  It’s a form of communal living going on out there in the hot dense forest, even during an awful drought.

The biggest activity going on in fungi-land, however, concerns the decaying fungi, referred to as “saprobic” fungi.  That is the largest group of all the fungi in the world, harkening back 2,400 million years ago when they lived in the ocean and decayed bacteria, long before plants ever existed.

The biggest group of saprobic fungi are the well-known “polypores.”  They are typified by those bracket-like mushrooms one often sees sticking out sideways from trees.  The surface under their caps is composed of thousands of tiny pores from which they release spores and hence get their name.  Polypores, generally speaking, have very tough tissue in them due to a substance called “chitin”, the same chemical found in lobster shells.  No amount of cooking will break this tissue down to make it edible, therefore most of them are not eaten.  

There are however some exceptions, as there always are in the study of fungi, such as the various poultry of the woods: Hen of the Woods, Chicken of the Woods and Rooster of the Woods.

Saprobic fungi are really just a bunch of silvan thieves.  These selfish woodland creatures do not share minerals and water with the trees in exchange for sugars, like their mycorrhizal cousins do. Instead, they reach deep into the vascular tissue of trees and extract sugars by breaking down the lignin and cellulose within, the very structure of the tree.  At the same time, they can extract what water exists within a living tree or from a rotting stump.  That is why saprobic fungi were found at last weekend’s Boston Mycological Club’s walk in Lynn.  We found a very young Chicken of the Woods that started to fruit but then quickly became desiccated.  A failed and fruitless effort launched by a miscalculating saprobe.  We also found Reishi (Ganoderma tsugae) growing on a massive hemlock tree and even a couple of token gilled fungi, who are also saprobic.  We found the Train Wrecker, Neolentinus lepideus which is famous for supposedly decaying enough railroad ties to actually cause a train wreck, and also the Velvet-Footed Pax or Fuzzy Foot, Tapinella atrotomentosa.

Many saprobic fungi can cause what is called “Brown Rot”.  They decay the lignin of the tree only, while leaving the cellulose behind.  The resultant chunks of geometrically shaped brown wood tissue eventually becomes part of the forest soil itself.  This is why conifer forests have a soft or spongy feel to the earth composing their forest floor.  The rot that occurs there is predominantly brown rot and the soil absorbs water more quickly, and more deeply, due to the porous effects of brown rot fungi than a hardwood forest floor does.

The remaining group of saprobic fungi cause what is called “White Rot” which involves the complete decay of the structural tissue of the tree due to the decay of the lignin, cellulose and the hemicellulose which comprises it.  Famous white rotters are Oyster Mushrooms and Shitakes.  In fact, the vast majority of all cultivated mushrooms are saprobic fungi because different substrates can be inoculated with spores and the fungi can begin their business of decay.

It’s easy to malign these silent thieves but if it wasn’t for their necessary work of decomposition our forests would be impenetrable due to masses of dead tissue, and minerals would not be released back into the soil for mycorrhizal fungi to come along later on and help the trees reabsorb.  It is a busy world out in the drought-ridden forest of fungi-land, but nature’s complex systems still plow on.

One is left to ponder what does it take to get mushrooms to start fruiting after a long drought?  Do they simply need repeated and ample rains?  Mycorrhizal fungi, such as Black Trumpets, Chanterelles or Boletes certainly do and will start fruiting if we get enough consistent rains.  One thunder storm a month is not enough.  Fungi are anything but stupid and they don’t want to use up their stored energy, their sugars, to produce fruiting bodies if they will only end up dry and desiccated within a few hours.  It is often theorized that Hen of the Woods will start fruiting in reaction to cooler temperatures at night, the coming of the fall season.  They don’t have such a need for moisture like mycorrhizal fungi do because they can get a lot of the moisture they need from inside the tree tissue itself.  They also may fruit due to increased carbon dioxide in the soil which occurs in the fall as bacterial growth is accelerated in combination with cooler temperatures.  

A lot of these systems are still unknown, and certainly provoke a thousand questions, but regular rains and more moderate temperatures would make every fruiting body happier out in fungi-land.  We look forward to the fall for that.

Gary Gilbert lectures on fungi, leads mushroom walks in the area and is a member of the Boston Mycological Club. He is the originator of “Mycocards”, flashcards for learning mushrooms by genus as well as having recipes in the recent Fantastic Fungi Community Cookbook.

mushrooms, drought, dry, soil, forest