Our Brilliant Bryosphere

Overlooked and unappreciated, mosses are always underfoot, but what are they doing down there?!

You might not even know much about mosses, but they are very simple plants that don't produce flowers and lack the internal tubing needed to move water to different tissues. Because mosses can't transport water to higher tissues, like a tree does, they grow very close to the ground and each leaf is only one cell layer thick so every cell has immediate access to water when it rains.

Mosses have such an intimate relationship with water that they thrive and turn bright green in the presence of moisture, but then very quickly shrivel and stop functioning when moisture dries up. This ability to respond to the presence or absence of water is nothing short of unbelievable, museum specimens that have been dry for over 100 years wake up and turn green within seconds of being wetted again.

Although they are tiny and very simple plants, mosses are all around us. In fact, we are rarely more than a few yards from mosses, even if we're not noticing them hidden in the cracks between bricks or tiles.

For this reason, scientists have taken a second look at mosses and discovered that mosses are one of the Earth's most dominant and vital life forms and are found in every habitat except the ocean. One recent estimate is that 10-20,000 species of moss cover approximately 6% of the planet's land surface, but researchers acknowledge this is likely a serious underestimate of moss's true dominance.

In many areas, mosses are so abundant that their primary productivity rivals or exceeds the productivity of all other plants around them. And mosses play such a vital role that they are known as ecosystem engineers because they drive the cycling of water, energy, and nutrients in an ecosystem. Furthermore, mosses associate with symbiotic cyanobacteria that produce so much nitrogen that they shape the global nitrogen cycle.

If that's hard to believe, think about this another way: Because mosses cover the ground like a lush carpet, they capture high levels of falling organic debris and atmospheric nutrients, then provide these nutrients to vast food webs that live at this mossy interface of soil, air, and water.

The web of life around moss is so vast and complex that scientists have coined the term bryosphere to signify its importance. This mossy world includes a dazzling number and variety of bacteria, algae, fungi, rotifers, tardigrades, nematodes, mites, springtails, and other life forms. For example, there can be over 225,000 springtails in a single yard of moss, and scientists have recorded 158 types of fungi on 27 moss stems.

When mosses are wet they leak out significant amounts of vital nutrients like dissolved organic carbon, nitrogen, and phosphorus that then power the bryosphere, and when mosses are dry they play another vital role by storing carbon. In fact, scientists now estimate that mosses store 6.5 billion tons of carbon, and that matters because this carbon would otherwise be released into our already oversaturated atmosphere and push climate change into overdrive.

Even without all these lofty impacts, mosses still matter because they stitch together soil while creating a barrier that protects soil from invasions by harmful pathogens. This same barrier also mediates and filters the exchange of water, gas, nutrients, and energy that are continuously percolating back and forth between the Earth and the atmosphere.

So, what are mosses doing down there? They may be humble, but they're holding a lot of pieces together!