Abstract
Climate warming alters plant composition and population dynamics of arctic ecosystems. In particular, an increase in relative abundance and cover of deciduous shrub species (shrubification) has been recorded. We inferred genetic variation of common shrub species (Alnus alnobetula, Betula nana, Salix sp.) through time. Chloroplast genomes were assembled from modern plants (n = 15) from the Siberian forest‐tundra ecotone. Sedimentary ancient DNA (sedaDNA; n = 4) was retrieved from a lake on the southern Taymyr Peninsula and analyzed by metagenomics shotgun sequencing and a hybridization capture approach. For A. alnobetula, analyses of modern DNA showed low intraspecies genetic variability and a clear geographical structure in haplotype distribution. In contrast, B. nana showed high intraspecies genetic diversity and weak geographical structure. Analyses of sedaDNA revealed a decreasing relative abundance of Alnus since 5,400 cal yr BP, whereas Betula and Salix increased. A comparison between genetic variations identified in modern DNA and sedaDNA showed that Alnus variants were maintained over the last 6,700 years in the Taymyr region. In accordance with modern individuals, the variants retrieved from Betula and Salix sedaDNA showed higher genetic diversity. The success of the hybridization capture in retrieving diverged sequences demonstrates the high potential for future studies of plant biodiversity as well as specific genetic variation on ancient DNA from lake sediments. Overall, our results suggest that shrubification has species‐specific trajectories. The low genetic diversity in A. alnobetula suggests a local population recruitment and growth response of the already present communities, whereas the higher genetic variability and lack of geographical structure in B. nana may indicate a recruitment from different populations due to more efficient seed dispersal, increasing the genetic connectivity over long distances.
Highlights
Ongoing climate change is altering plant composition and biomass in arctic ecosystems
We sequenced and assembled 15 chloroplast genomes based on modern DNA
The results showed that 13 out of 16 variations previously identified in our chloroplast genome sequences from modern A. alnobetula assemblies were covered by sedimentary ancient DNA (sedaDNA) reads from shotgun metagenomics or hybridization capture experiments (Figure 5)
Summary
Ongoing climate change is altering plant composition and biomass in arctic ecosystems. Continuous vegetation turnover from open forest to single-tree tundra in southern Taymyr over the last 7,100 years was reflected by a decrease of Alnus and the increase of Salix, both in a palynological study (Niemeyer et al, 2017) and a metabarcoding study using sedimentary ancient DNA (sedaDNA) records (Epp et al, 2018) These alternating contractions and expansions of shrubs due to climatic fluctuations during the Quaternary have probably affected the geographical distribution of plastid haplotypes in modern shrub populations (Casazza et al, 2016). We compare genetic variation through time to infer shrub population dynamics in common shrub species of the Siberian forest-tundra ecotone (Alnus alnobetula, Betula nana, Salix sp.). Paired-end sequencing (2 × 150 bp) was performed on an Illumina NextSeq 500 platform (Illumina)
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