Pollen Chemistry as the Next Generation Tool in Palaeoecological Research - Theory, Methods and Application

Pollen produced by plants can be preserved in the sediments of lakes and bogs for thousands, or even millions of years. When this happens, the youngest is preserved in the top layers of the sediments, and older pollen is buried deeper and deeper. If the plant communities in the surrounding environment have changed, then so too will the pollen in the sediments. This pollen provides a window into past ecosystem changes in the past. Because we generally lack information on past ecosystem changes beyond the last 100-200 years, pollen datasets vital sources of data for learning about how plants responded to environmental changes in the past, how this affects present-day patterns of biodiversity, and how plants might respond to environmental changes (e.g. climate changes) in the future. In PollChem we were investigating a new technique for the analysis of fossil pollen grains. The overall aim of the project was to investigate whether the chemical changes in fossil-pollen grains could be used to unlock secrets about past ecosystems. At the onset of the project, a number of studies had indicated that the chemical composition of pollen responds to changes in environmental conditions (e.g. exposure to solar UV-B radiation). This is exciting, because although solar UV-B radiation may be a key variable for understanding drivers of biodiversity change in the past, it is presently impossible to reconstruct UV-B radiation beyond the past few decades. Pollen chemistry could be an extremely valuable tool for Earth scientists for understanding how and why species evolve and even go extinct over time. But before we applied pollen chemistry to reconstruct the past it was crucial to understand how pollen chemistry responds to changes in UV-B radiation in the modern environment. In PollChem we developed a new set of experimental approaches and studies to estimate how plants respond to UV-B radiation, and made some major leaps forward towards applying pollen chemistry methods to ancient-sediment sequences. In addition, studies had also demonstrated that different species of plants had different pollen-chemistry characteristics. This means it might be possible to use chemical variations in pollen to identify grains to species/ genus level. This would give palaeoecologists a new tool for reconstructing past environments. In PollChem we showed that pollen-chemistry techniques can resolve differences at the sub-genus level within the group, oaks, using modern pollen, and investigated the best methods and protocols to apply this understanding to fossil sequences.

The RCN Young Research Talent award has had important outcomes for the career development of the PI and the associated PhD student. The PI has supervised his first PhD student through the project, published his first paper as a senior author, and has now established own pollen-chemistry research group and laboratory space at the University of Bergen. An additional major outcome has been the increased interdisciplinary research between palaeoecological and photobiological, and vibrational spectroscopy fields. As result, the new set of field and greenhouse experimental techniques which, because of their flexible experimental design, has massive potential for future research. We are now well-placed to conduct future studies which aim to develop quantitative reconstruction models of UV-B radiation and for applying pollen chemistry techniques for better identification of fossil pollen grains. Moving forward the project therefore is expected to have a major long-term impact on the field.

The projected environmental changes of the 21st century will have profound impacts on Earth's biodiversity and its associated ecosystem functions, but basic, baseline information related to drivers of change and their variability is lacking for many ecosystems. Palaeoecology uses the plant remains (e.g. fossil pollen) preserved in lake sediments to fill this critical knowledge gap. Sediments are natural data-loggers, but information obtained from sediments is limited by current techniques. There is a need for new tools and methods to generate novel ecological insights from the information from sediment cores. PollChem works at the frontiers of a new and emerging technique with the potential to trigger the next revolution in palaeoecology. Recent studies indicate that the chemical constituents of pollen respond to changes in environmental conditions and are also reflective of phylogenetic patterns. Since components of this pollen-chemical signature can remain preserved in sediments over thousands of years, pollen chemistry has the potential to provide new and unparalleled levels of detail for a range of palaeoecological applications. PollChem provides, for the first time, an integrated framework which implements the full scope of pollen chemistry techniques to three major palaeoecological applications. We will (i) quantitatively investigate the response of pollen chemistry to UV-B exposure along elevation gradients in Norway and the Pyrenees, and validate this approach using state-of-the-art greenhouse experiments. It will then use this model to reconstruct ultra-violet radiation (UV-B) for the from a Holocene sediment core as a validation-through-time test for a new pollen-based UV-B proxy; (ii) extend these techniques to reconstruct UV-B across the Permian-Triassic transition (ca. 252 million years ago), where UV-B exposure has been proposed as a key extrinsic driver of mass-extinction; and (iii) investigate whether species differences in pollen chemistry can improve taxonomic precision within a palaeoecological dataset of Quercus taxa. This work will place UiB at the centre of a new and emerging technique with general applicability to palaeoecological science.