Bolshoe Toko Vegetation reconstruction from sedimentary ancient DNA metabarcoding data. BT_Vegetation

Links between climate, species composition and species richness are of particular importance in understanding how boreal ecosystems will respond to the ongoing climate change. This study aims to reconstruct changes in terrestrial vegetation composition and taxa richness during the glacial late Pleistocene and the interglacial Holocene in the sparsely studied region of south-east Yakutia (Siberia) by using pollen and sedimentary ancient DNA (sedaDNA) records. Both pollen and sedaDNA metabarcoding data using the trnL g and h markers were analysed from a sediment core from the lake Bolshoe Toko. Both approaches were used to reconstruct the vegetation composition, while metabarcoding method was used to investigate changes in plant taxa richness. The complementarity of pollen and sedaDNA allowed a robust estimation of regional and local past terrestrial vegetation composition around Bolshoe Toko during the last ~40,000 years. Both proxies suggest that south-eastern Siberia in the late Pleistocene was covered by open steppe-tundra dominated by herb taxa such as graminoids or forbs with patches of shrubs, confirming that steppe-tundra extended this far south in Siberia. Both proxies show disturbance at the transition between the late Pleistocene and the Holocene suggesting a period with scarce vegetation and high sedimentation rates. A switch in vegetation composition is observed in both proxies during the Holocene with an increased number of trees and shrubs compared to herb taxa and the appearance of new tree taxa during the early Holocene around the lake’s vicinity. The sedaDNA method suggests that the late Pleistocene steppe-tundra vegetation supported a higher number of terrestrial plant taxa than the forested Holocene. This could be explained, for example, by the keystone herbivore hypothesis which posits that late Pleistocene megaherbivores were able to maintain a high plant diversity by strongly interacting with plant communities. A second hypothesis discussed is the broadly accepted species-area hypothesis as steppe-tundra covered such an extensive area during the late Pleistocene.