Mosses are small, non-vascular plants that do not “eat” food like animals. As autotrophs, they create their own energy, relying on environmental inputs rather than consuming organic matter. Their survival strategy involves absorbing necessary components directly from the atmosphere and surface water instead of drawing them from the soil through roots.
Generating Energy Through Photosynthesis
Mosses generate their own fuel through photosynthesis, a process powered by sunlight. Like most green plants, they possess chlorophyll, which captures light energy. This energy is used to convert atmospheric carbon dioxide ($\text{CO}_2$) and water into glucose, a simple sugar that serves as the plant’s food.
The resulting glucose molecules are carbohydrates that provide the energy required for all metabolic functions, growth, and reproduction. Oxygen is released as a byproduct of this chemical conversion.
How Moss Absorb Water and Minerals
Mosses lack the vascular system found in larger plants, meaning they cannot transport water and nutrients efficiently from a centralized root system. They rely on ectohydry, where the movement of water and minerals occurs primarily on the exterior of the plant. Water and dissolved minerals are absorbed directly across the entire surface of the plant body, including the stem and leaves.
Structures resembling roots, called rhizoids, function mainly as anchors to secure the moss to its substrate, such as a rock or a tree trunk. They do not perform the primary absorption role that true roots do. Water is drawn up through the densely packed moss carpet through capillary action, similar to how water moves up a paper towel.
Absorption of dissolved nutrients and water happens cell by cell via diffusion and osmosis across the thin leaves. This highly efficient surface absorption allows mosses to rapidly take up moisture from rain, mist, or fog. Specialized mosses, such as Sphagnum, have large, dead, water-holding cells called hyaline cells that act like tiny sponges, storing many times their own weight in water.
Environmental Factors Dictating Nutrient Sources
Since mosses absorb water and minerals directly through their exposed surfaces, they are highly dependent on atmospheric deposition. This includes nutrients dissolved in rainwater, mist, or airborne dust particles. Minerals like potassium, calcium, and magnesium are washed onto the plant surface and absorbed with the water.
The substrate, whether soil, rock, or bark, plays a limited role as a direct nutrient source for most mosses. Epiphytic mosses growing high on tree branches receive almost all of their nutrients from precipitation and canopy drip. Terrestrial mosses may anchor in soil, but they still primarily absorb nutrients directly from the water film on their surface.
Nitrogen, a building block for proteins, is often acquired through symbiotic relationships with cyanobacteria. These bacteria live within the moss colonies and perform nitrogen fixation, converting atmospheric nitrogen into a usable form. This fixed nitrogen is then available to the moss.