AUTHOR=Hamard Samuel , Robroek Bjorn J. M. , Allard Pierre-Marie , Signarbieux Constant , Zhou Shuaizhen , Saesong Tongchai , de Baaker Flore , Buttler Alexandre , Chiapusio Geneviève , Wolfender Jean-Luc , Bragazza Luca , Jassey Vincent E. J. 

TITLE=Effects of Sphagnum Leachate on Competitive Sphagnum Microbiome Depend on Species and Time

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02042

DOI=10.3389/fmicb.2019.02042

ISSN=1664-302X

ABSTRACT=<p>Plant specialized metabolites play an important role in soil carbon (C) and nutrient fluxes. Through anti-microbial effects, they can modulate microbial assemblages and associated microbial-driven processes, such as nutrient cycling, so to positively or negatively cascade on plant fitness. As such, plant specialized metabolites can be used as a tool to supplant competitors. These compounds are little studied in bryophytes. This is especially notable in peatlands where <italic>Sphagnum</italic> mosses can dominate the vegetation and show strong interspecific competition. <italic>Sphagnum</italic> mosses form carpets where diverse microbial communities live and play a crucial role in <italic>Sphagnum</italic> fitness by regulating C and nutrient cycling. Here, by means of a microcosm experiment, we assessed to what extent moss metabolites of two <italic>Sphagnum</italic> species (<italic>S. fallax</italic> and <italic>S. divinum</italic>) modulate the competitive <italic>Sphagnum</italic> microbiome, with particular focus on microbial respiration. Using a reciprocal leachate experiment, we found that interactions between <italic>Sphagnum</italic> leachates and microbiome are species-specific. We show that both <italic>Sphagnum</italic> leachates differed in compound richness and compound relative abundance, especially sphagnum acid derivates, and that they include microbial-related metabolites. The addition of <italic>S. divinum</italic> leachate on the <italic>S. fallax</italic> microbiome immediately reduced microbial respiration (−95%). Prolonged exposition of <italic>S. fallax</italic> microbiome to <italic>S. divinum</italic> leachate destabilized the food web structure due to a modulation of microbial abundance. In particular, leachate addition decreased the biomass of testate amoebae and rotifers but increased that of ciliates. These changes did not influence microbial CO<sub>2</sub> respiration, suggesting that the structural plasticity of the food web leads to its functional resistance through the replacement of species that are functionally redundant. In contrast, <italic>S. fallax</italic> leachate neither affected <italic>S. divinum</italic> microbial respiration, nor microbial biomass. We, however, found that <italic>S. fallax</italic> leachate addition stabilized the food web structure associated to <italic>S. divinum</italic> by changing trophic interactions among species. The differences in allelopathic effects between both <italic>Sphagnum</italic> leachates might impact their competitiveness and affect species distribution at local scale. Our study further paves the way to better understand the role of moss and microbial specialized metabolites in peatland C dynamics.</p>