Lichens cover nearly 7% of the earth’s surface and in eastern Canada, lichen woodlands occupy over 300,000 km2. Reindeer lichens (genus Cladonia), are the main component of lichen woodlands and they play a crucial role in boreal forest ecology. We study, for the first time, the bacterial community of four species of reindeer lichens from eastern North America’s boreal forests. Using the 16S rRNA gene, we characterize the bacterial community of 189 lichen samples. We aim to analyse the effect of host-identity and geography in the bacterial community composition and structure, verify the presence of a common core bacteria and identify the most abundant core taxa. Our results suggest that host-lichen identity does not determine bacterial community composition and structure in reindeer lichens, but we confirm the influence of geography in shaping the diversity and abundance of bacteria associated to Cladonia stellaris. We also reveal that reindeer lichens share a reduced common core bacteria composed exclusively by Alphaproteobacteria. Northern lichen woodlands exhibit a significantly higher diversity and abundance of bacteria associated to Cladonia stellaris than southern lichen woodlands. The presence of the species Methylorosula polaris in the core bacteria is evident and may have a particular importance for reindeer lichens.

The southern Appalachian (SA) is one of the most biodiversity−rich areas in North America and has been considered a refugium for many disjunct plant species, from the last glacial period to the present. Our study focuses on the SA clonal hornwort, Nothoceros aenigmaticus J. C. Villarreal & K. D. McFarland. This hornwort was described from North Carolina and is widespread in the SA, growing on rocks near or submerged in streams in six and one watersheds of the Tennessee (TR) and Alabama (AR) Rivers, respectively. Males and female populations occur in different watersheds, except in the Little Tennessee (TN) River where an isolated male population exists ca. 48 km upstream from the female populations. The sex ratio of 1:0 seems extreme in each population. In this study, we use nuclear and organellar microsatellites from 250 individuals from six watersheds (seven populations) in the SA region and two populations from Mexico (23 individuals). We, then, selected 86 individuals from seven populations and used genotyping by sequencing to sample over 600 bi-allelic markers. Our results suggest that the SA N. aenigmaticus and Mexican plants are a nested within a clade of sexual tropical populations. In the US populations, we confirm an extreme sex ratio and only contiguous US watersheds share genotypes. The phylogenetic analysis of SNP data resolves four clusters: Mexican populations, male plants (Little Pigeon and Pigeon river watersheds) and two clusters of female plants; one from the Little Tennessee and Hiwassee Rivers (TR) and the other from the Ocoee (TR) and Coosa (AR) Rivers. All clusters are highly differentiated (Fst values over 0.9). In addition, our individual assignment analyses and PCAs reflect the phylogenetic results grouping the SA samples in three clades and recovering males and female plants with high genetic differentiation (Fst values between 0.5 and 0.9 using microsatellites and bi-allelic markers). Our results point to Pleistocene events shaping the biogeographical pattern seen in US populations. The extreme sex ratio reflects isolation and highlights the high vulnerability of the populations in the SA.

Background and AimsTremendous progress have been recently achieved in host-microbe research, however, there is still a surprising lack of knowledge in many taxa. Despite its dominance and crucial role in boreal forest, reindeer lichens have until now received little attention. We characterize, for the first time, the bacterial community of four species of reindeer lichens from Eastern North America’s boreal forests. We analysed the effect of two factors (host-identity and geography) in the bacterial community composition, we verified the presence of a common core bacteriota and identified the most abundant core taxa.MethodsMorphological and molecular lichen species delimitation was performed based on the ITS region. The bacterial community of around 200 lichen samples was characterised using the 16S rRNA gene.Key ResultsOur results showed that host-lichen identity does not determine bacterial community composition in reindeer lichens, but we confirmed the influence of geography in shaping the diversity and abundance of bacteria associated to the species Cladonia stellaris from lichen woodlands. We also revealed that reindeer lichens share a reduced common core bacteriota composed exclusively by Proteobacteria.ConclusionsThe bacterial community in reindeer lichens is not host-selective. Northern lichen woodlands exhibit a significant higher diversity and abundance of bacteria associated to Cladonia stellaris. Nevertheless, the specific role of those bacteria as well as the process of host colonization remains to be determined. Elucidating these two aspects would be key to have a better understanding of the whole boreal ecosystems. The reduced and not diverse core bacteriota of reindeer lichens might be due to the larger size of our study area. The presence of the species Methylorosula polaris in the core bacteriota is evident and might have a particular importance for reindeer lichens.

Lichens are one of the main structural components of plant communities in the North American boreal biome. They play a pivotal role in lichen woodlands, a large ecosystem situated north of the closed-crown forest zone, and south of the forest-tundra zone. In Eastern Canada (Quebec), there is a remnant LW found 500 km south of its usual distribution range, in the Parc National des Grands-Jardins, originated mainly because of wildfires. We inferred the origin of the lichen Cladonia stellaris from this LW and assessed its genetic diversity in a postfire succession. METHODS: We genotyped 122 individuals collected across a latitudinal gradient in Quebec. Using the software Stacks, we compared four different approaches of locus selection and single-nucleotide polymorphism calling. We identified the best fitting approach to investigate population structure and estimate genetic diversity of C. stellaris. RESULTS: Populations in southern Quebec are not genetically different from those of northern LWs. The species consists of at least four phylogenetic lineages with elevated levels of genetic diversity and low co-ancestry. In Parc National des Grands-Jardins, we reported high values of genetic diversity not related with time since fire disturbance and low genetic differentiation among populations with different fire histories. CONCLUSIONS: This first population genomic study of C. stellaris is an important step forward to understand the origin and biogeographic patterns of lichen woodlands in North America. Our findings also contribute to the understanding of the effect of postfire succession on the genetic structure of the species.

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