The interactive effect of phenolics and microorganisms on Sphagnum spore viability and germination

Allelopathic interactions with microorganisms likely govern plant community assembly, yet their effects on spore germination of Sphagnum, a critical carbon-sequestering genus, remains unknown. Using a hummock sphagnum, S. fuscum and a hollow sphagnum, S. squarrosum, we tested the effects of three phenolic compounds and their mixture common in peatland water on spore germination with and without microorganisms. Both individual and mixture of phenolic compounds increased Sphagnum spore viability. In presence of microorganisms, the viability of S. fuscum spores reduced from 44 to 36 % when cultivated in ultrapure water but it was increased from 52 to 63 % in peat water. Phenolic compounds had inhibitory effect on microbial biomass with stronger effect in peat water (mixture of phenolics) than in individual phenolic compounds. The two Sphagnum species showed different response to allelopathy and microorganisms. While both species showed bet-hedging strategy, the hummock species maintained low and hollow species maintained high germinability. We conclude that Sphagnum-derived phenolics can maintain spore viability by inhibiting microorganisms. We suggest that the inhibitory effect of allelochemicals on microorganisms can be an important mechanism for maintaining viable spore bank in peatlands.