Master’s Thesis 2018 60 ECTS Faculty of Environmental Sciences and Natural Resource Management Kari Klanderud Pernille B. Eidesen, UNIS Inger G. Alsos, UiT The Holocene vegetation history of an isolated, high-arctic plant diversity hot spot Linn Margrethe Høeg Voldstad Master of Science in Ecology Acknowledgements This study comprises data from many different scientific fields and proved to demand experience and knowledge quite far beyond my prior experience. I owe many thanks to everyone who helped me and made this study possible: Wesley Farnsworth (The University centre in Svalbard) and Anders Schomacker (The Arctic University of Norway) for access to the sub-samples of the sediment cores and all core-related data (project 16/35 funded by the Carlsberg Foundation). The ECOGEN research group in Tromsø, and in particular Youri Lammers, Peter Heintzman and Dilli Rijal for help with bioinformatics (Youri), guidance in the aDNA lab (Peter) and for running the metabarcoding PCRs and pooling and cleaning the PCR products (Peter and Dilli). Johannes Sand Bolstad for assisting with field work. Lena Håkansson (The University Centre in Svalbard) for guidance and help with interpreting geological data. Jan Christensen’s endowment for financial support. Special thanks go to all my supervisors, and in particular Pernille B. Eidesen for giving me the opportunity to explore the flora in Ringhorndalen, and in general for her enthusiasm and advice during the whole process. Abstract Through high throughput sequencing of ancient, environmental DNA collected from lake sediment cores (sedaDNA), this study revealed postglacial vegetation change during the last ~12.000 years in a high-Arctic plant diversity hot spot in Svalbard. Geochemical proxy data for environmental variation in the catchment area obtained from high resolution X-radiographic scans were combined with the sedaDNA record to detect local Holocene climate variations. The findings were in accordance with main climatic shifts on Svalbard identified by previous studies and indicated an early warm and species-rich postglacial period followed by fluctuating cool and warming events throughout the Holocene record. Thermophilic species with their current distribution outside the catchment area of the studied lake had reoccurring presence throughout the Holocene sedaDNA record, suggesting postglacial periods when thermophilic arctic species had broader distribution ranges than today. This supports the hypothesis of isolated relict populations in Ringhorndalen, the place in Svalbard with the highest registered diversity of vascular plants and several remarkable and isolated plant populations located far north of their normal distribution range. 2 Introduction Paleoecological records provide insight into past vegetation. This information can be combined with knowledge about past climates in order to anticipate impacts from global warming on species diversity and composition in an area (Allen & Huntley 1999). Knowledge about the historic plant species composition can even be used to increase knowledge about past climates (Alsos et al. 2015). Next generation sequencing methods have drastically increased the potential for molecular investigations in paleoecological studies in the last decade (Taberlet et al. 2007; Parducci et al. 2017). In particular have ancient DNA from sediments (sedaDNA) shown to be an efficient tool for reconstructing past vegetation and species diversity in environments where more traditional paleobotanical methods can be challenging due to low pollen and plant macrofossil concentrations (Taberlet et al. 2007; Sønstebø et al. 2010; Jørgensen et al. 2012; Pedersen et al. 2013; Alsos et al. 2015; Parducci et al. 2017). Ancient DNA studies can be particularly useful to reconstruct past vegetation in the arctic regions, because low local pollen concentrations impede traditional methods (Vasil’chuk 2005) and the cold conditions ensure preservation of the genetic material (Hofreiter et al. 2001). Even if DNA is highly degraded, which is increasingly likely with older sample material (Hofreiter et al. 2001), studies from arctic regions have proven the value of modern sequencing technologies when analysing DNA directly from environmental samples, such as sediments (Sønstebø et al. 2010). Preservation and recovery of sedaDNA is particularly good in lake sediments (Parducci et al. 2017; Alsos et al. 2018). Lake sediments also hold information about regional climate change because they trap detrital and organic material as well as organic material produced within the lake (Gjerde et al. 2017). Magnetic and geochemical properties obtained from high-resolution X-radiographic scans can be used as proxies to study major patterns in abiotic environmental changes in the catchment area of the studied lake. The variation in scanned profiles of magnetic susceptibility and lithogenic, geochemically stable and conservative elements such as aluminium (Al), silica (Si), potassium (K), titanium (Ti), iron (Fe) and rubidium (Rb) can reflect changes in glacial-derived minerogenic input (Sandgren & Snowball 2001), weathering regimes (Rothwell & Croudace 2015) or the amount of inorganic detrital input to a lake (Røthe et al. 2015), thus be used to infer climate variations. The elements calsium (Ca) and silica (Si) normalized against Ti and and iron (Fe) normalized against manganese (Mn) can be used as proxies for biological productivity within the lake (Balascio et al. 2011; Kylander et al. 2011; 3 Melles et al. 2012; Alsos et al. 2015; Gjerde et al. 2017). SedaDNA and plant macrofossil records from lakes in western Spitsbergen have shown that thermophilic plant species probably had a broader distribution on Spitsbergen in early Holocene, a warmer postglacial period (Birks 1991; Alsos et al. 2015). An area that assumingly has remains from this vegetation, is Ringhorndalen (Eidesen et al. 2013). This tributary valley east of Wijdefjorden, Spitsbergen, have been described as an ‘Arctic hotspot’ as defined by Elvebakk (2005a), with numerous registrations of thermophilous species. One remarkable botanical feature of Ringhorndalen is that many of the unusual plant species observed there seem to be spatially distant from their normal distribution range. Some populations represent some of the northernmost known sites for the species worldwide and in some cases the only known location for Svalbard and even Europe (Eidesen et al., unpublished). In this study I investigated a c. 12 000-year-old sediment core from a high-arctic lake in Ringhorndalen using sedaDNA, sediment properties and geochemical proxy data, in order to reconstruct changes in vegetation composition and evaluate these changes in a context of a changing Holocene climate. It is assumed that the postglacial period c. 9000-5000 years ago was remarkably warmer than present (Hyvärinen 1970; Birks 1991; Birks et al. 1994; Salvigsen & Høgvard 2006; Miller et al. 2010; Alsos et al. 2015; Mangerud & Svendsen 2018), thus vegetation reconstructions from this period can provide information about possible future vegetation development in scenarios with anticipated warming in the Arctic. The research questions I aimed to answer were: (i) How has the composition of plants in the catchment area of the studied high-arctic lake developed during the Holocene? (ii) How does the variation in climatic conditions revealed from biotic and abiotic sources match throughout the depth of the core? (iii) How is the current vegetation around the lake represented in the modern, uppermost sediment layers? (iv) Are the unusually thermophilic vascular plant species found in Ringhorndalen today relicts from populations established during the Holocene warm periods? To address these research questions, historic postglacial plant species assemblages were obtained from amplicon high-throughput sequencing (HTS) of sedaDNA sampled chronologically throughout the core. Obtained vegetation data were compared to geochemical data acquired through high-resolution X-radiographic scans (Croudace et al. 2006). Plant species assemblages representing the current vegetation were obtained from HTS of DNA in 4 the uppermost sediment layer. The current vegetation data from modern sediments were then compared to the present floristic composition acquired from on-site vegetation analysis. Results from the sedaDNA analysis were also used to investigate the origin of unusually thermophilic species registered in Ringhorndalen. Species that matched between ancient and present plant assemblages were assumed to represent long-time presence, and to disclose these populations as remnants from a former more widespread vegetation from the warmer early Holocene (Eidesen et al. 2013). Alternatively, these isolated populations can be recent colonizers, and must be seen in context with ongoing climate change. In the latter case, the findings of this study represent an important contribution to the understanding of species immigration to Svalbard. As Ringhorndalen is rarely visited by people, any recent plant establishments here are likely to be due to natural long-distance dispersal, as former studies have shown to frequently occur in Svalbard (Alsos et al. 2007). Methods Study area Indre Wijdefjorden National Park was established in 2005 as a result of thorough botanical investigations that revealed remarkable findings at several locations in the area (Elvebakk & Nilsen 2002). These findings included populations of rare and unusually thermophilous plants in an arctic context. In addition, a new vegetation