The bryophyte genus Sphagnum occurs as a dominant vegetation component in peat-forming bogs and fens worldwide. The peat mosses are known to have physical and chemical properties which keep their environment wet, acidic and unfavourable for most higher plants and microbes. In this paper, the production and further fate of secondary metabolites produced by Sphagnum representatives are reviewed, with special reference to their ecological significance for the Sphagnum plants and for the bog ecosystem as a whole. The organochemical compounds produced by Sphagnum discussed here can be roughly divided into two groups. A first major group of compounds are the phenolics, secondary metabolites, the most important of which is sphagnum acid (p-hydroxy-(i(carboxymethyl)-cinnamic acid). This is a monophenolic which is specific for this genus and has been found in all representatives studied so far. This phenolic is present in the cell fluids but also in three-dimensional polymeric networks, together with other phenolics such as gallic acid, in the cell walls. The second group of compounds are carbohydrates, in particular uronic acids such as galacturonic acid, which also form large polymeric molecules, named ‘sphagnan’, associated with the cell walls. The polymeric phenols give the cell walls the rigor needed for the large water-holding capacity of the hyaline cells. They also will provide a defence against herbivores and diseases, although this has not been investigated in any systematic way. The monomeric phenolics are excreted into the bog water and may have allelopathic functions. The polyuronic acids in the cell walls give the peat mosses their high cation exchange capacity, which enables them to firmly bind metals and nutrients. The effects of these metabolites on the functioning of the bog ecosystem are mostly associated with their inhibitory effect on decomposition, which is of great importance for the peat storage function. The monophenolics excreted in the bog water slow down microbial decomposition in the acrotelm, and recycling of nutrients is relatively rapid after the death of the cells. The phenolics in the cell walls prohibit the microbial breakdown of all cell wall polysaccharides, and this protective action may persist in deep peat layers for thousands of years. The polymeric networks of phenolics release tannins in deep peat layers. These tannins, together with the sphagnan which is released in the catotelm, have a tanning effect on proteins and further slow down the peat decomposition.

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Acta botanica neerlandica

CC BY 3.0 NL ("Naamsvermelding")

Koninklijke Nederlandse Botanische Vereniging

J.T.A. Verhoeven, & W.M. Liefveld. (1997). The ecological significance of organochemical compounds in Sphagnum. Acta botanica neerlandica, 46(2), 117–130.