Winter Decomposers

Fungi make their living a variety of ways.  Some are parasites taking nutrients from living organisms.  Some are symbionts associated with the roots of plants that transfer inorganic nutrients to the plant in exchange for sugar and other organic molecules.  And some fungi decompose formerly living material.  These decomposers mainly break down dead plant parts. Without the decomposers, a walk in the woods would be wading through a sea of dropped leaves, a tangle of downed branches and impassable barriers of dead tree trunks.   We usually don’t see these vital components of the ecosystem except when they make their reproductive structures called fruiting bodies or more familiarly, mushrooms.  Most of the fungal biomass is in microscopic threads of cells called hyphae.  The hyphae of the decomposers growth throughout the dead plant parts and release enzymes that break down highly resistant plant polymers like cellulose and lignin.  The fungus then absorbs the breakdown products of these polymers and the plant parts are recycled.  Winter is not typically a good time for finding mushrooms in this area but the decomposers are an exception. 

Turkey tail fungus, Trametes versicolor, on a rotting log

On some recent hikes, we found several of these winter decomposers. One prominent fungus on dead tree trunks is the turkey tail (Trametes versicolor).  The flat caps of the turkey tail grow in large groups on dead trees.  They are quite striking with alternating bands of varying shades of brown, gray and white that resembles the tail of a turkey.  On the underside of the cap are small oval pores that produce the spores of the fungus. These pore-bearing fungi are Polypores, classified in the family Polyporaceae. The spores float through the air and if lucky enough to land on a dead tree, can establish another colony of turkey tail fungus. 

Fruiting bodies of Poronidulus conchifer

Small white mushrooms growing on small dead branches is Poronidulus conchifer another Polypore. The pores are found on the lower side of the fruiting body.  This fungus is closely related to the turkey tail.  The scientific name quite descriptive. The genus, Poronidulus, is from the Latin meaning “little nest with pores”.  When the fruiting body is small it is curled up and look like little bird's nests.  Since it is a The species name, conchifer, is Latin for “conch bearing” because the larger fruiting bodies look very shell-like. 

A common large mushrooms growing on downed logs and on dying live trees is the oyster mushroom Pleurotus ostreatus. This fungus is has a worldwide distribution and is a major decomposer of wood.  It is also a choice, edible mushroom.  The whitish caps of the fruiting body resemble oysters and that gives it both its common name and the species name (ostreatus is from Latin for oyster).  The fruiting body usually grows in groups on a tree trunk or log.  The underside of the mushroom bears spore-producing gills typical of members of the order Agaricales, the gilled mushrooms.  Oyster mushrooms make their living decomposing wood but have a more ominous source of nutrients.  Pleurotus ostreatus is also a carnivore.  Hyphae of the oyster mushroom produce droplets of a toxic protein that paralyzes nematodes found in and on the rotting wood.  Oyster mushroom hyphae then invade the body of the paralyzed nematode and consume the unfortunate worm from the inside. 

 

Oyster mushroom (Pleurotus ostreatus) showing spore-producing gills

Oyster mushroom on log with their typical oyster shape

Even in winter, the process of decomposition goes on, carried out by a group of fascinating fungi.