Abstract
Although sedimentary ancient DNA (sedaDNA) has been increasingly used to study paleoecological dynamics (Schulte et al., 2020), the approach has rarely been compared with the traditional method of pollen analysis for investigating past changes in the vegetation composition and diversity of Arctic treeline areas. Here, we provide a history of latitudinal floristic composition and species diversity based on a comparison of sedaDNA and pollen data archived in three Siberian lake sediment cores spanning the mid-Holocene to the present (7.6–0 cal ka BP), from northern typical tundra to southern open larch forest in the Omoloy region. Our results show that the sedaDNA approach identifies more plant taxa found in the local vegetation communities, while the corresponding pollen analysis mainly captures the regional vegetation development and has its limitations for plant diversity reconstruction. Measures of alpha diversity were calculated based on sedaDNA data recovered from along a tundra to forest tundra to open larch forest gradient. Across all sites, sedaDNA archives provide a complementary record of the vegetation transition within each lake’s catchment, tracking a distinct latitudinal vegetation type range from larch tree/alder shrub (open larch forest site) to dwarf shrub-steppe (forest tundra) to wet sedge tundra (typical tundra site). By contrast, the pollen data reveal an open landscape, which cannot distinguish the temporal changes in compositional vegetation for the open larch forest site and forest-tundra site. Increasing Larix pollen percentages were recorded in the forest-tundra site in the last millenium although no Larix DNA was detected, suggesting that the sedaDNA approach performs better for tracking the local establishment of Larix. Highest species richness and diversity are found in the mid-Holocene (before 4.4 ka) at the typical tundra site with a diverse range of vegetational habitats, while lowest species richness is recorded for the forest tundra where dwarf-willow habitats dominated the lake’s catchment. During the late Holocene, strong declines in species richness and diversity are found at the typical tundra site with the vegetation changing to relatively simple communities. Nevertheless, plant species richness is mostly higher than at the forest-tundra site, which shows a slightly decreasing trend. Plant species richness at the open larch forest site fluctuates through time and is higher than the other sites since around 2.5 ka. Taken together, there is no evidence to suggest that the latitudinal gradients in species diversity changes are present at a millennial scale. Additionally, a weak correlation between the principal component analysis (PCA) site scores of sedaDNA and species richness suggests that climate may not be a direct driver of species turnover within a lake’s catchment. Our data suggest that sedaDNA and pollen have different but complementary abilities for reconstructing past vegetation and species diversity along a latitude.
Highlights
Arctic ecosystems are assumed to be very sensitive to climate change
We find that our sedimentary ancient DNA (sedaDNA) records are more sensitive to sitespecific vegetation compositional change than the pollen records (Figures 3, 5, 6)
We found a few wet sedges occurred in this typical tundra site in the late Holocene, which might be attributed to gradual permafrost thawing, and a simultaneous expansion of shrubs marked by the increased relative abundance of Betula (Blok et al, 2010)
Summary
Shifts in vegetation composition and plant richness (or other alpha diversity measures) over the past few decades have been assigned to Arctic warming (Elmendorf et al, 2012; Pearson et al, 2013; Myers-Smith et al, 2015, 2019). Plant richness of the tundra is typically lower than in forest areas and is associated with harsh climate conditions (Chapin and Körner, 1995; Khitun et al, 2016). Species diversity in present-day tundra areas is expected to increase in the course of forest expansion related to future warming. There is speculation that plant richness may decrease in the course of warming due to the reduction of habitats for arctic-adapted species (Callaghan et al, 2004). Whether plant richness in tundra areas will decrease or increase under future climate-driven vegetation turnover is largely unknown
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