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Sphagnum mosses mediate long-term carbon accumulation in peatlands. Given their functional role as keystone species, it is important to consider their responses to ecological gradients and environmental changes through the production of phenolics. We compared the extent to which Sphagnum phenolic production was dependent on species, microhabitats and season, and how surrounding dwarf shrubs responded to Sphagnum phenolics. We evaluated the phenolic profiles of aqueous extracts of Sphagnum fallax and Sphagnum magellanicum over a 6-month period in two microhabitats (wet lawns versus dry hummocks) in a French peatland. Phenolic profiles of water-soluble extracts were measured by UHPLC-QTOF-MS. Andromeda polifolia mycorrhizal colonization was quantified by assessing the intensity of global root cortex colonization. Phenolic profiles of both Sphagnum mosses were species-, season- and microhabitat- dependant. Sphagnum-derived acids were the phenolics mostly recovered; relative quantities were 2.5-fold higher in S. fallax than in S. magellanicum. Microtopography and vascular plant cover strongly influenced phenolic profiles, especially for minor metabolites present in low abundance. Higher mycorrhizal colonization of A. polifolia was found in lawns as compared to hummocks. Mycorrhizal abundance, in contrast to environmental parameters, was correlated with production of minor phenolics in S. fallax. Our results highlight the close interaction between mycorrhizae such as those colonizing A. polifolia and the release of Sphagnum phenolic metabolites and suggest that Sphagnum-derived acids and minor phenolics play different roles in this interaction. This work provides new insight into the ecological role of Sphagnum phenolics by proposing a strong association with mycorrhizal colonization of shrubs.

[Ring-U14C] p-hydroxybenzoic acid (POH) translocation during radish germination and early seedling growth was studied to compare two culture conditions (sterile/non-sterile) and two modes of POH extraction (ethanol/oxidizing). Quantification of POH in organs was performed by grinding them in a mortar with ethanol or by combusting them in a biological oxidizer. Comparison of these extraction methods revealed that the oxidizer provides higher POH concentrations than grinding. Uptake and translocation of POH into radish seedlings occurred in the first 24 hr with the highest accumulation in cotyledons. POH in cotyledons ranged from 8 to 12.4 mumol g-1 FW. Two forms of POH were found in seedlings, an ethanol-soluble one and a "bound" one. After 96 hr incubation, half of the recovered POH was "bound" in roots and hypocotyls. POH recovery in seedlings was also higher under axenic rather than non-axenic conditions. POH was degraded into 14CO2 by microorganisms under non-sterile cultures, its concentration in culture medium decreased from 10(-3) to 10(-4) M between the first and the fourth day of incubation. Choice between sterile and non-sterile culture conditions as a method depends on particular research objectives. Non-sterile methods can be used to reflect natural processes whereas sterile methods can be used if the objective is to determine allelochemical penetration and biological effects on target plants.