In a subterranean society, what do mushrooms eat?
In the underground worlds of various fantasy and sci-fi settings, a common thread is fungus. Instead of plants, they eat fungus. Instead of fodder, they feed their livestock fungus. They brew fungus into alcohol. They build structures out of fungal stalks.
But fungus is a living organism; it doesn’t just pop up out of nowhere. It consumes organic matter: rotting wood, dead animals, feces, etc. In the real world, there’s not a lot of migration between the surface world and caverns, and the small amount of detritus that does make its way underground is only eaten by micrororganisms, which facilitate small crustacean predators, and the amphibians that eat the crustaceans. There’s no incentive for larger animals to go much deeper than a few feet to get out of the rain.
In these fictional worlds, what do the mushrooms eat? For this I have two possible explanations:
Magic. The mushrooms eat magic. They’re able to take ambient magical energy in the world and transform that into physical growth. It’s elegant, it’s weird, it’s fun, but it’s also a copout. Nothing wrong with a copout, but how can we get more creative with it?
Chemosynthesis. What ecosystem on earth is also completely lightless yet supports a healthy ecology? Bottom of the ocean. Organisms down here either rely on what’s called “marine snow” (small rotting pieces of dead organisms and feces that fall down into the depths), “whale falls” (when a whale, large enough to avoid being completely torn apart by predators falls down the bottom), or geothermal vents: essentially underwater volcanoes which spew hot hydrocarbons into the ocean, which bacteria can use to create the building blocks of life. Those bacteria are then eaten by larger predators.
What if we take this concept of deep-sea chemosynthesis and apply it to a fictional cavern ecosystem? Hot volcanic gases and ancient petroleum are consumed by tiny microorganisms that live in a symbiotic relationship with fungi, which are in turn eaten by the horrors that lurk in the ever-present shadow. This would create a bottom-up food chain, where the very deepest, most inhospitable parts of caves form the bedrock of the ecosystem, in addition to the top-down system of organic runoff.
I dunno, this idea has been stuck in my brain for a long time and I wanted to share. What’re your thoughts? Any cool ideas you have?