BIOGEOCHEMICAL FEATURES OF ORDOVICIAN TERRESTRIAL ECOSYSTEMS INFERRED FROM A MICROBIOME FOR EARLIEST-DIVERGING MODERN PLANT LINEAGE SAMPLED FROM A REMOTE LOCALE MODELING ORDOVICIAN CONDITIONS

Little is known about terrestrial biotas present during the Great Ordovician Biodiversification event. Because recent fossil and molecular diversification evidence indicates that the modern peat moss lineage originated >450 Ma, peat mosses may represent Earth’s earliest terrestrial vegetation. Globally abundant modern peat mosses host diverse microbiota. Such partnerships are recognized to provide significant ecosystem services, e.g. organic carbon sequestration, methane oxidation, and nitrogen fixation. Hence, peat moss microbiomes provide insight into the biogeochemical impacts of early vegetation, which is thought to have occupied remote islands and experienced nutritional stress and episodes of high UV radiation. We used shotgun metagenomics to assess the microbiome of a peat moss sampled from a remote island locale matching hypothesized Ordovician terrestrial conditions, namely, Chilean sub-Antarctic Navarino Island, long subject to high UV beneath the southern ozone hole. We filtered 16S, 18S, 23S, and 28S rDNA sequences from contigs assembled from long-read Roche 454 and deep Illumina sequencing and employed them to infer prokaryotic and eukaryotic microbiome composition at generic and higher taxonomic levels. Comparison of bacterial diversity, including >75 genera represented by >100 sequence reads and >250 genera at >10 reads, to diversity reported from previous studies of peat mosses or peatlands indicated the operation of recognized peatland biogeochemical functions (e.g., carbon sequestration, methane oxidation, and nitrogen fixation). Many additional types of biogeochemically-significant metabolism were inferred, including magnetite-formation. Eukaryotic features included >45 protist genera, some of pivotal evolutionary significance, as well as distinctive fungal associations and ancient lineages of microscopic invertebrate animals. Our approach provides a new window into early Ordovician terrestrial vegetation and its biogeochemical impacts.