Holocene chloroplast genetic variation of shrubs (Alnus alnobetula, Betula nana, Salix sp.) at the Siberian tundra-taiga ecotone.. Alnus alnobetula, Betula nana, Salix sp

Climate warming alters plant composition and biomass of arctic and alpine ecosystems. In particular have an increase in relative abundance and cover of deciduous shrub species (shrubification) been recorded. We compared genetic variation through time to infer shrub population dynamics in common shrub species (Alnus alnobetula, Betula nana, and Salix sp.). Plastid DNA from modern plants (n = 15) and sedimentary ancient DNA (sedaDNA; n = 4) from the Siberian forest-tundra ecotone were analyzed by shotgun sequencing and a hybridization capture approach. For A. alnobetula, analyses of modern DNA showed low intra-species genetic variability and a clear geographical structure in haplotype distribution. On the other hand, B. nana showed high intra-species genetic diversity and weak geographical structure. Analyses of sedaDNA from the Taymyr region revealed decreased relative abundance of Alnus during the last 5000 years, whereas Betula and Salix increased. The comparison between genetic variations identified in modern DNA and sedaDNA showed that Alnus variants were maintained through the last 7000 years in the Taymyr region. In accordance with modern individuals, the variations retrieved in Betula sedaDNA showed higher genetic diversity. Our results suggest that shrubification has species-specific trajectories. For A. alnobetula, the recent population recruitment process toward the north seems to be a phenological response of an already present local community, whereas the higher genetic variability and lack of geographical structure in B. nana may indicate efficient recruitment from different populations, as well as hybridization and introgression processes. The latter is in line with former findings showing that B. nana has efficient seed dispersal, and readily hybridize when growing in sympatry with other Betula species.