When people hear the word mutualism, images of bees and flowers or oxpeckers on rhinos appear in their minds. But mutualism can occur between some of the smallest organisms on this planet. In 2013, scientists discovered that the relationship between moss and cyanobacteria provided much-needed nitrogen compounds for boreal trees. In a way, you could say this is a 3-way mutualistic relationship!
Plants require CO2, water, and sunlight to make glucose. But what happens to the glucose afterwards? It turns out that plant cells use this glucose to do all sorts of cool things… like build cellulose, lignin, and most importantly, make proteins and enzymes. One necessary ingredient for protein production is nitrogen, but most of the nitrogen on Earth is stuck in the atmosphere as nitrogen gas. This gas is unusable by living organisms and totally useless.
Some plants (like legumes) have symbiotic relationships with nitrogen-fixing bacteria. These tiny root-dwellers take atmospheric nitrogen gas and turn it into ammonia. What about non-legume plants? Worry not. Usable nitrogen enters the soil any time an animal pees, poops, or decomposes. This is why cow manure is such a great fertilizer… and so are dead bodies.
In the boreal forest, decomposition of dead things takes a bit longer because of the low temperatures. However, mosses have taken a liking to the damp, chilly environment and grow in abundance in on the forest floor. They help drive decomposition of leaf litter and provide a safe place for cyanobacteria colonies to grow. In return, the cyanobacteria fix nitrogen. So, by having this moss-cyanobacteria team living near them, trees are able to get all the nitrogen they need.
Curious to read the whole paper or use this cool relationship in your classroom? Check out the paper, paper summary, and lesson plan suggestions here.