Fossil pollen and spores as a tool for reconstructing ancient solar-ultraviolet irradiance received by plants : an assessment of prospects and challenges using proxy-system modelling

Ultraviolet-B radiation (UV-B, 280-315 nm) constitutes less than 1% of the total solar radiation that reaches the Earth's surface but has a disproportional impact on biological and ecological processes from the individual to the ecosystem level. Absorption of UV-B by ozone is also one of the primary heat sources to the stratosphere, so variations in UV-B have important relationships to the Earth's radiation budget. Yet despite its importance for understanding atmospheric and ecological processes, there is limited understanding about the changes in UV-B radiation in the geological past. This is because systematic measurements of total ozone and surface UV-B only exist since the 1970s, so biological or geochemical proxies from sediment archives are needed to reconstruct UV-B irradiance received at the Earth surface beyond the experimental record. Recent developments have shown that the quantification of UV-B-absorbing compounds in pollen and spores have the potential to provide a continuous record of the solar-ultraviolet radiation received by plants. There is increasing interest in developing this proxy in palaeoclimatic and palaeoecological research. However, differences in interpretation exist between palaeoecologists, who are beginning to apply the proxy under various geological settings, and UV-B ecologists, who question whether a causal dose-response relationship of pollen and spore chemistry to UV-B irradiance has really been established. Here, we use a proxy-system modelling approach to systematically assess components of the pollen-and spore-based UV-B-irradiance proxy to ask how these differences can be resolved. We identify key unknowns and uncertainties in making inferences about past UV-B irradiance, from the pollen sensor, the sedimentary archive, and through the laboratory and experimental procedures in order to target priority areas of future work. We argue that an interdisciplinary approach, modifying methods used by plant ecologists studying contemporary responses to solar-UV-B radiation specifically to suit the needs of palaeoecological analyses, provides a way forward in developing the most reliable reconstructions for the UV-B irradiance received by plants across a range of timescales.Peer reviewe

Ancient DNA from speleothems: opportunity or challenge?

Ancient environmental DNA retrieved from sedimentary records (sedaDNA) can complement fossil-morphological approaches for characterizing Quaternary biodiversity changes. PCR-based DNA metabarcoding is so far the most widely used method in environmental DNA studies, including sedaDNA. However, degradation of ancient DNA and potential contamination, together with the PCR amplification drawbacks, have to be carefully considered. Here we tested this approach on speleothems from an Alpine cave that, according to a previous palynomorphological study, have shown to contain abundant pollen grains. This offers a unique opportunity for comparing the two methods and, indirectly, trying to validate DNA-based results. The plant taxa identified by sedaDNA are fewer than those by pollen analysis, and success rate of PCR replicates is low. Despite extensive work performed following best practice for sedaDNA, our results are suboptimal and accompanied by a non-negligible uncertainty. Our preliminary data seem to indicate that paleoenvironmental DNA may be isolated from speleothems, but the intrinsic weakness of PCR-based metabarcoding poses a challenge to its exploitation. We suggest that newly developed methods such as hybridization capture, being free from PCR drawbacks and offering the opportunity to directly assess aDNA authenticity, may overcome these limitations, allowing a proper exploitation of speleothems as biological archive

Detection of ice core particles via deep neural networks

Insoluble particles in ice cores record signatures of past climate parameters like vegetation dynamics, volcanic activity, and aridity. For some of them, the analytical detection relies on intensive bench microscopy investigation and requires dedicated sample preparation steps. Both are laborious, require in-depth knowledge, and often restrict sampling strategies. To help overcome these limitations, we present a framework based on flow imaging microscopy coupled to a deep neural network for autonomous image classification of ice core particles. We train the network to classify seven commonly found classes, namely mineral dust, felsic and mafic (basaltic) volcanic ash grains (tephra), three species of pollen (Corylus avellana, Quercus robur, Quercus suber), and contamination particles that may be introduced onto the ice core surface during core handling operations. The trained network achieves 96.8 % classification accuracy at test time. We present the system's potential and its limitations with respect to the detection of mineral dust, pollen grains, and tephra shards, using both controlled materials and real ice core samples. The methodology requires little sample material, is non-destructive, fully reproducible, and does not require any sample preparation procedures. The presented framework can bolster research in the field by cutting down processing time, supporting human-operated microscopy, and further unlocking the paleoclimate potential of ice core records by providing the opportunity to identify an array of ice core particles. Suggestions for an improved system to be deployed within a continuous flow analysis workflow are also presented

The importance and direction of current and future plant-UV research : break-out session discussions at the UV4Plants Network Meeting in Bled (April 15th -18th , 2018)

During the 2nd Network Meeting of UV4Plants at Bled (14th–18th April, 2018) the delegates engaged in a group discussion of prescient questions concerning the future of in plant-UV research. The discussion group was tasked to identify the most valuable directions for plant UV research to take, and to create a coherent framework for how to move the field forward. Here, the outcome of these discussions is summarised in sections that follow the composition of discussion groups as ideas taken from a molecular, biochemical and physiological perspective followed by those from an ecological and plant production perspective. In each case, first basic research questions are considered and then applications and methodological considerations are put forward. Finally, some common ground bringing the two perspectives together is discussed, with the aim of solving scaling problems and ways in which the UV4Plants network might be put to good use.Peer reviewe

Notulae to the Italian alien vascular flora: 11

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions. Nomenclatural and distribution updates published elsewhere are provided as Suppl. material 1

Age of the Mt. Ortles ice cores, the Tyrolean Iceman and glaciation of the highest summit of South Tyrol since the Northern Hemisphere Climatic Optimum

In 2011 four ice cores were extracted from the summit of Alto dell'Ortles (3859 m), the highest glacier of South Tyrol in the Italian Alps. This drilling site is located only 37 km southwest from where the Tyrolean Iceman, similar to 5.3 kyrs old, was discovered emerging from the ablating ice field of Tisenjoch (3210 m, near the Italian-Austrian border) in 1991. The excellent preservation of this mummy suggested that the Tyrolean Iceman was continuously embedded in prehistoric ice and that additional ancient ice was likely preserved elsewhere in South Tyrol. Dating of the ice cores from Alto dell'Ortles based on Pb-210, tritium, beta activity and C-14 determinations, combined with an empirical model (COPRA), provides evidence for a chronologically ordered ice stratigraphy from the modern glacier surface down to the bottom ice layers with an age of similar to 7 kyrs, which confirms the hypothesis. Our results indicate that the drilling site has continuously been glaciated on frozen bedrock since similar to 7 kyrs BP. Absence of older ice on the highest glacier of South Tyrol is consistent with the removal of basal ice from bedrock during the Northern Hemisphere Climatic Optimum (6-9 kyrs BP), the warmest interval in the European Alps during the Holocene. Borehole inclinometric measurements of the current glacier flow combined with surface ground penetration radar (GPR) measurements indicate that, due to the sustained atmospheric warming since the 1980s, an acceleration of the glacier Alto dell'Ortles flow has just recently begun. Given the stratigraphic-chronological continuity of the Mt. Ortles cores over millennia, it can be argued that this behaviour has been unprecedented at this location since the Northern Hemisphere Climatic Optimum