Evidences of Bryophyte allelochemical interactions: the case of Sphagnum.
Résumé
In most terrestrial ecosystems allelochemical interactions involved vascular plants. Nevertheless, bryophytes represent also a crucial group found in many ecosystems with a specific morphology and physiology (e.g. secondary metabolism). Among bryophytes, Sphagnum genus is of particular interest because they form a dense homogeneous carpet which is slowly decomposed (the peat) in peatlands. Such ecosystems represent a terrestrial sink of carbon sink and so are crucial to be studied, especially under a climate change. Objectives of this chapter were 1) to synthesize current bryophyte allelochemical interactions and 2) to illustrate recent research on Sphagnum with the case of Sphagnum fallax phenolics (production and degradation) recovered in a french peatland. The top layer of living Sphagnum represents the active allelopathic part where water-soluble phenolics were mostly recovered. Their concentrations were found to change along the seasons. The transformation of phenolic compounds are performed by an enzymatic system O2 (phenoloxidases) or H2O2 (peroxidases) dependent. Sphagnum-peroxidases constituted the main oxidative system and fungal-phenoloxidases were proposed to be regulated by phenolics. Moreover, Sphagnum was able to regulate its secondary metabolism under a climate forcing by decreasing its phenolic concentrations. Allelopathic potential of Sphagnum phenolics was stated with their role in the microdistribution of associated Sphagnum micro-organisms. Finally, Sphagnum extracts also strongly delayed Pine and Lolium germination seeds and inhibited Lolium radicle growth and delayed Raphanus and Pinus radicles. Ecological and agronomic perspectives of Sphagnum extracts are discussed