moss: A Surprising Climate Saviour?

A new study shines a light on one of nature’s best carbon sinks.

Moss might seem like an unassuming little plant, one that can’t possibly have a global impact. In fact, for years, scientists barely analysed its ecological role precisely because of its meek facade. But researchers recently undertook the first global survey of mosses, spanning 123 sites across every continent, and what they found was shocking. It turns out that moss currently locks away an immense 6.42 billion tonnes of carbon, making it a vital part of our planet's carbon cycle. But how is this carbon stored? And can we use this knowledge to prevent further climate change?

For the past few decades, scientists have studied in excruciating detail how plants can absorb carbon dioxide from the atmosphere and safely store it. Through the process of photosynthesis, plants can turn atmospheric carbon dioxide and water into hydrocarbon molecules, which they use to fuel themselves and build their carbon-rich bodies. We now know that through complex interactions with the soil microbiome when the plant is alive and through decay once it is dead, these plants can safely store large amounts of carbon in stable soil deposits for many years at a time. This is why numerous carbon-offsetting schemes are focused on mangrove or rainforest protection.

However, the plants that these scientists studied were vascular plants. These have stems or trunks that prop up the plant and root systems. But vascular plants’ long-distant cousins, the non-vascular plants, are also known as mosses—at least when they’re terrestrial. These non-vascular plants lack the roots needed to interact with a soil microbiome, and their bodies contain none of the decay-resistant carbon-rich molecule lignin that vascular plants use to build their rigid bodies. A plant’s lignin can stay intact in soils for centuries, locking away the carbon, which is so effective that scientists previously believed lignin accounted for 30% of the carbon stored by plants annually. The rest comes from cellulose deposits and soil microbiome interaction, both of which mosses implement to a far lesser extent.

As such, many scientists assumed that mosses played almost no role in the carbon cycle in comparison to their vascular relatives.

But a recent study in Nature has turned this notion on its head. They took data from 123 moss-rich sites across all of the world’s continents and also analysed existing experimental studies on mosses to try and figure out mosses' true part in the global ecology.