Abstract
The unique environment of a 4m-thick, free-floating peat island within the Posta Fibreno lake (Central Italy) was analyzed using DNA-based techniques to assess bacterial and fungal community members identity and abundance. Two depths were sampled at 41 and 279 cm from the surface, the former corresponding to an emerged portion of Sphagnum residues accumulated less than 30 yrs ago, and the latter mainly consisting of silty peat belonging to the deeply submerged part of the island, dating back to 1520–1660 AD. The corresponding communities were very diverse, each of them dominated by a different member of the Delta-proteobacteria class for prokaryotes. Among Eukaryotes, Ascomycota prevailed in the shallow layer while Basidiomycota were abundant in the deep sample. The identity of taxa partitioning between acidic surface layer and neutral core is very reminiscent of the differences reported between bogs and fens respectively, supporting the view of Posta Fibreno as a relic transitional floating mire. Moreover, some microbial taxa show an unusual concurrent species convergence between this sub-Mediterranean site and far Nordic or circumpolar environments. This study represents the first report describing the biotic assemblages of such a peculiar environment, and provides some insights into the possible mechanisms of its evolution.
Highlights
Free-floating mires are particular environments consisting of emergent vegetation rooted in highly organic buoyant mats, moving on the lake surface naturally due to the release of gases generated by the decomposition of the underlying peat-mat layer[1]
The ammonia monooxygenase gene, catalyzing the first step of nitrification, was sought in two versions; archeal and bacterial, the former of which was below detectable levels, whereas the second was more abundant in the deeper (PFB4 #16–17, hereafter referred to as ‘deep’) sample as it appeared two cycles earlier when compared to the superficial one (PF2 #46, hereafter referred to as ‘shallow’)
To properly frame the habitat for data interpretation, it is worth recalling that, upon chemical[8], botanical[6] and limnological analyses[9], this lake was classified as lotic-lentic, i.e., a system that encompasses both the features of lake-type environments and those of river-type ones. The latter trait is due to a constant flow of karstic groundwater causing a continuous washout effect of dilution and a fast water removal
Summary
Free-floating mires are particular environments consisting of emergent vegetation rooted in highly organic buoyant mats, moving on the lake surface naturally due to the release of gases generated by the decomposition of the underlying peat-mat layer[1]. The free-floating island at Posta Fibreno is a transitional mire, where ombrotrophic bog vegetation has evolved over time from minerotrophic fen vegetation probably as a consequence of buoyancy[5]. While this is the most common evolutionary sequence found in continental peatlands that have formed from terrestrialization, almost no data are present in literature on the evolution of deep floating islands. DNA was extracted from the two peat layers and analyzed by RealTime PCR and Generation Sequencing (NGS) approaches in order to unravel its unique evolution mechanisms and provide some evidences about microbial adaptation to environmental changes over centuries
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