How do bog mosses capture carbon in waterlogged environments, where the availability of CO₂ may be limited? The answer may lie in a place that has so far been little investigated: the surface of their cells.
This is the finding of an international study published in the journal *New Phytologist*, conducted on behalf of Italy by researchers from the Institute for Research on Terrestrial Ecosystems of the National Research Council (CNR-IRET), together with colleagues from Spain, France, Germany, the United States and Japan. The research demonstrates, for the first time, a relationship between the chemical properties of Sphagnum cell surfaces and their photosynthetic performance under submerged conditions, linking two aspects that have hitherto been studied predominantly in isolation: surface chemistry and the physiology of photosynthesis.
Peatlands cover around 3 per cent of the Earth’s surface, yet they store almost a third of the carbon present in the planet’s soils. A key part of this capacity depends on mosses of the genus Sphagnum, which play a central role in peat formation and the functioning of these ecosystems. To better understand the mechanisms underlying carbon uptake, the researchers analysed 20 species of Sphagnum and four laboratory-cultured clones, combining an analysis of the chemical properties of cell surfaces with measurements of photosynthesis and chlorophyll fluorescence across a wide pH gradient.
The results show that species differ in the quantity of reactive chemical groups present on the cell surface and that a higher presence of these groups is associated with greater CO₂ assimilation. Photosynthesis was maintained in all species even under water-saturated conditions, but with different responses depending on the species and pH. In particular, Sphagnum palustre L. showed a particularly stable response across the entire pH range analysed, suggesting a greater capacity to adapt to environmental variations.
‘Surface chemistry has long been studied to understand processes such as ion exchange, acidification and the binding of pollutants,’ explains Anna Di Palma, a researcher at CNR-IRET and lead author of the study. ‘Our work shows that the chemistry of biosurfaces should also be taken into account when studying how Sphagnum mosses sequester carbon in aquatic environments.’
“Peatlands are important allies in the fight against climate change, because they accumulate peat under conditions of waterlogging and oxygen deprivation, storing vast quantities of carbon removed from the atmosphere,” continues the scientist. “With global warming and the degradation of these ecosystems, however, peat decomposes more rapidly and can release CO₂ and CH₄, transforming these resources from carbon sinks into sources of greenhouse gases, thereby contributing to further warming.”
Surface chemistry may therefore play a broader role than previously recognised: not only in carbon uptake, but also in the strategies by which different Sphagnum species respond to environmental conditions. Species characterised by more reactive surfaces have also shown a greater potential for binding dissolved metals, a finding that opens up possible applications for biomonitoring, water treatment and the restoration of peatlands.
A further finding concerns Sphagnum clones grown under axenic conditions, that is, in the absence of associated microorganisms. These clones retained the key chemical characteristics observed in natural mosses, confirming their value as experimental models for the study of Sphagnum and as a potential basis for sustainable cultivation programmes and Sphagnum farming. Overall, the study suggests that to understand the role of Sphagnum in peatlands, one must consider different scales, ranging from cell surface chemistry to the functioning of the entire ecosystem. The differences observed between species may, in fact, help to explain their distribution along gradients of pH and water availability and, consequently, influence the functioning of peatlands and their role in the global carbon cycle.
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