A mushroom that is always an exciting find is Stropharia rugosoannulata. Also known as the wine cap because of its red wine-colored pileus, I find this fungus growing on manmade woodchips and other natural, fine woody debris. The fruiting bodies of Stropharia rugosoannulata have an affinity for gardens and grow rather large, which helps explain its other common name-the garden giant. Michael Kuo from mushroomexpert.com explains that you can also find this mushroom on stream beds were spring floods have occurred. Many times, when I do find other edible species, I don’t find enough to make a substantial meal, so I tend to leave those specimens along with the ecological services they provide. However, when I come across Stropharia rugosoannulata, I usually find them in large enough numbers that I know I can at least make a yummy side dish. The edibility of this robust species is not the only reason I get excited when I find them growing from the forest floor. They have evolved some pretty cool adaptations too.
Developing Stropharia rugosoannulata. Photo by Cory Zanker.
There was a time in Earth’s past when there were no woody structures being synthesized in any ecosystem. As soon as plants ‘figured out’ how to form wood, plants went through a period of adaptive radiation, growing larger than they ever have before. You see, wood is a fascinating tissue that is extremely strong and flexible. Its physical properties are quite amazing, but its chemical structure is the main reason why many plants today still use wood. Wood is made up of long-chained polymers called lignin as well as fibers of cellulose. Both of these organic substances are notoriously ‘cheap’ to synthesize for the plant. Plants don’t allocate many scarce forest floor nutrients during the formation of wood because the substance is made up of mostly carbon; a resource plants have an abundance of.
From a plants perspective, wood is extremely efficient to synthesize. This structural trait allowed plants to grow much larger, which massively increased their photosynthetic area. After wood, these organisms started interacting with their environment more than ever before, and drastically changed the evolutionary trajectory of other forest floor inhabitants. With this new abundant carbon rich resource, it was only a matter of time before the fungal kingdom started taking advantage.
The wine cap. Photo by Cory Zanker.
Before wood, fungi already functioned as a saprotroph, breaking down dead organic matter. Some of these saprotrophs made a transition to a more specialized ectomycorrhizal ecology, when plants become more photosynthetically active. Other saprotrophs continued their decomposer lifestyle and over millennia ‘figured out’ how to break down the long polymer chains that make up wood. If you go on a hike today in an old growth forest, you will be astonished at all the large woody debris laying around. It seems like fungi will never run out of food, but what makes wood an efficient tissue to synthesize for plants, does not make it a prime food source for fungi.
Again, wood is carbon rich but overall, nutrient poor. For this reason, many saprotrophic fungi also take advantage of other organisms that live in wood to supplement their diet; nematodes. I have talked about nematode trapping fungi more than once already. The mechanisms I have talked about include constrictive lassos that tighten when nematodes enter the hyphal loop, adhesive knobs, and hyphal nets. The trapping structures that Stropharia rugosoannulata utilize are different than the mechanisms I mention before and show that the species has evolved these strategies independently.
Spiked acanthocytes immobilize nematode. Zouhar et al. 2013.
Stropharia rugosoannulata produce spiked cells within their substrate called acanthocytes. These sharp cells penetrate and immobilize unfortunate nematodes and allow the fungus to break down and absorb nutrients like nitrogen and phosphorus within the nematodes tissue. Studies conducting bioassays on the wine cap show that this trapping mechanism works incredible. In 2006 Hong Luo and his team found that just after 15 minutes, Stropharia rugosoannulata immobilized 90% of the nematodes introduced to the fungus. In a similar, more recent 2013 study, researchers showed 100% immobilization after 24 hours.
Acanthocyte of S. rugosoannulata. Zouhar et al. 2013.
Stropharia rugosoannulata is an amazing species I love encountering on my fungal forays. Not only because I know a snack is coming my way, but because of this interesting niche it interacts with. Yes, the species breaks down woody substrates, but it also takes full advantage of the nematodes that live in those same substrates. So much so, that Stropharia rugosoannulata can be used as a biocontrol agent. Many crops are susceptible to root rots that are caused by soil inhabiting nematodes, so inoculating croplands with these nematode trapping fungi is a reliable way to control these plant pathogens without using harmful chemicals. In this present day, it’s imperative that we utilize sustainable ways to enhance crop production without risking the health of natural ecosystems. We should continue to look for ecological services forest floor inhabitants can provide, because it is pretty clear that we are only scratching the surface.