Sphagnum genus have a key role in peatland functioning by creating the conditions for the accumulation of one third of the world's soil carbon. However, Sphagnum secondary metabolites are poorly quantified compared with vascular plants. Recent works has shown that total phenolic compounds produced by living Sphagnum influence microbial communities, fungal enzymatic activities and vascular plant mycorrhizae. They also vary according to the season and are reduced by global warming. It is then timely to better understand how Sphagnum secondary metabolism responds to global change.

We investigated how climate warming affect Sphagnum specific phenolics (Sphagnum acids) using a metabolic profiling approach. Two sphagnum species (S. magellanicum and S. fallax) were collected along an experimental site in a peatland of Jura (Frasne, 25) within two microhabitats (wet lawn versus dry hummock) submitted to an increase of +1°C thanks to the installation of Open top chamber since 2008. Sphagnum acids of ethanolic extracts (v/v20/80%) were evaluated by UHPLC MS-Qtof.

Our results identified four sphagnum acid forms (i.e. a simple sphagnum acid, a glycosylated form, a conjugated form with uronic acids and an ethylester form). Their production was majoritary in the capitulum and varied between months and species. Global warming had little effect on the production of sphagnum acids for both species. Interestingly, the microhabitat influenced only the production of glycosylated and conjugated with uronic acids forms in S. fallax. For this species, the sphagnum acids production was positively correlated to the air temperature and mire water pH. For S. magellanicum, they were negatively correlated to air temperature and water level but positively to the Sphagnum pH. These results underline the importance to study the production and regulation of sphagnum acids among Sphagnum species. Allelopathic roles of these metabolites between Sphagnum species, vascular plants and microbial communities offer interesting perspectives.