Holocene floristic diversity and richness in northeast Norway revealed by sedimentary ancient DNA (sedaDNA) and pollen

Abstract

We present a Holocene record of floristic diversity and environmental change for the central Varanger Peninsula, Finnmark, based on ancient DNA extracted from the sediments of a small lake (sedaDNA). The record covers the period c. 10 700 to 3300 cal. a BP and is complemented by pollen data. Measures of species richness, sample evenness and beta diversity were calculated based on sedaDNA sampling intervals and 1000‐year time windows. We identified 101 vascular plant and 17 bryophyte taxa, a high proportion (86%) of which are still growing within the region today. The high species richness (>60 taxa) observed in the Early Holocene, including representatives from all important plant functional groups, shows that modern shrub‐tundra communities, and much of their species complement, were in place as early as c. 10 700 cal. a BP. We infer that postglacial colonization of the area occurred prior to the full Holocene, during the Pleistocene‐Holocene transition, Younger Dryas stadial or earlier. Abundant DNA of the extra‐limital aquatic plant Callitriche hermaphroditica suggests it expanded its range northward between c. 10 200 and 9600 cal. a BP, when summers were warmer than present. High values of Pinus DNA occur throughout the record, but we cannot say with certainty if they represent prior local presence; however, pollen influx values >500 grains cm−2 a−1 between c. 8000 and 7300 cal. a BP strongly suggest the presence of pine woodland during this period. As the site lies beyond the modern tree limit of pine, it is likely that this expansion also reflects a response to warmer Early Holocene summers.

Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada

“…This relatively productive lake environment was likely a result of high summer lake water temperatures and/or a long ice‐free season, and is indeed mirrored in high temperatures inferred from brGDGTs between 6.7 and 6.3 ka. The presence of Callitriche hermaphroditica early in the sed aDNA record, and its dominance (77%–98% of reads) between 6.8 and 6.4 ka, provides further evidence of warm conditions during this time; in the modern, this species requires minimum July temperatures of ~14°C (Clarke et al, ; Väliranta et al, ), ~6°C warmer than the modern July mean temperature in Iqaluit. Successional processes and soil development in the surrounding catchment also likely promoted high lacustrine productivity during this time (Engstrom, Fritz, Almendinger, & Juggins, ; Fritz & Anderson, ).…”

Shotgun Environmental DNA, Pollen, and Macrofossil Analysis of Lateglacial Lake Sediments From Southern Sweden

“…It is also a positive result since a larger number of taxa could be identified using the three proxies. Some major taxa detected by pollen (e.g., Pinus, Ulmus, Chenopodiaceae, Poaceae, Apiaceae), some assigned to long-distance transport, were not recorded either by the macrofossil or eDNA data sets, confirming that pollen does not contribute to eDNA in lake sediments (Parducci et al, 2015;Alsos et al, 2016;Pedersen et al, 2016;Sjögren et al, 2016;Clarke et al, 2018), likely because only few pollen grains per species are present in each sediment sample (in our case 623 on average Table S1) and each pollen grain contains only two or three cells.…”

Paleo‐metagenomics of North American fossil packrat middens: Past biodiversity revealed by ancient DNA

“…When taxa are identified in molecular data but not in the macrofossil record, true aDNA could be present in the form of pollen or other trace material (including unidentifiable macrofossils) that is difficult to access or not typically processed when studying packrat midden contents. The presence of DNA in the absence of pollen or other known tissue is not necessarily surprising and has been observed in other systems, particularly in ancient sedimentary DNA (Clarke, Edwards, Brown et al, ; Parducci et al, ). It may also be that DNA fragments are being misclassified due to missing data in the reference database or bias toward more complete genomic records (Harbert, ).…”