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The sizes and shapes of ice crystals influence the radiative properties of clouds, as well as precipitation initiation and aerosol scavenging. However, ice crystal growth mechanisms remain only partially characterized. We present the growth processes of two complex ice crystal habits observed in Arctic mixed‐phase clouds during the Ny‐Ålesund AeroSol Cloud ExperimeNT campaign. First, are capped‐columns with multiple columns growing out of the plates' corners that we define as columns on capped‐columns. These ice crystals originated from cycling through the columnar and plate temperature growth regimes, during their vertical transport by in‐cloud circulation. Second, is aged rime on the surface of ice crystals having grown into faceted columns or plates depending on the environmental conditions. Despite their complexity, the shapes of these ice crystals allow to infer their growth history and provide information about the in‐cloud conditions. Additionally, these ice crystals exhibit complex shapes and could enhance aggregation and secondary ice production. Plain Language Summary: Snowflakes formed in the atmosphere have a wide variety of shapes and sizes and no two snowflakes are identical. The reason for this infinite number of shapes is that the environmental temperature and relative humidity prevailing during the snowflakes' growth determine their exact aspects. Thus, the prevailing environmental conditions can be determined from the shape of snowflakes, and become more complicated with increased shape complexity. During a measurement campaign in the Arctic, we identified two complex snowflake types and the history of environmental conditions in which they grew in. We inferred that some snowflakes were recirculating to higher or lower parts of the clouds and that others had collided with cloud droplets that froze on their surface at the early stage of their growth. These snowflakes may enhance the formation of new snowflakes and the initiation of precipitation. Key Points: A large variety of ice crystal sizes and shapes were observed in Arctic mixed‐phase clouds with a holographic imagerThe growth history of two types of complex ice crystals was inferred from their shapesThese ice crystals could enhance aggregation and secondary ice production [ABSTRACT FROM AUTHOR]

The Arctic is warming at more than twice the rate of the global average. This warming is influenced by clouds, which modulate the solar and terrestrial radiative fluxes and, thus, determine the surface energy budget. However, the interactions among clouds, aerosols, and radiative fluxes in the Arctic are still poorly understood. To address these uncertainties, the Ny-Ålesund Aerosol Cloud Experiment (NASCENT) study was conducted from September 2019 to August 2020 in Ny-Ålesund, Svalbard. The campaign's primary goal was to elucidate the life cycle of aerosols in the Arctic and to determine how they modulate cloud properties throughout the year. In situ and remote sensing observations were taken on the ground at sea level, at a mountaintop station, and with a tethered balloon system. An overview of the meteorological and the main aerosol seasonality encountered during the NASCENT year is introduced, followed by a presentation of first scientific highlights. In particular, we present new findings on aerosol physicochemical and molecular properties. Further, the role of cloud droplet activation and ice crystal nucleation in the formation and persistence of mixed-phase clouds, and the occurrence of secondary ice processes, are discussed and compared to the representation of cloud processes within the regional Weather Research and Forecasting Model. The paper concludes with research questions that are to be addressed in upcoming NASCENT publications. [ABSTRACT FROM AUTHOR]

There is growing evidence that root-associated fungi have important roles in Arctic ecosystems. Here, we assess the diversity of fungal communities associated with roots of the ectomycorrhizal perennial herb Bistorta vivipara on the Arctic archipelago of Svalbard and investigate whether spatial separation and bioclimatic variation are important structuring factors of fungal community composition. We sampled 160 plants of B. vivipara from 32 localities across Svalbard. DNA was extracted from entire root systems, and 454 pyrosequencing of ITS1 amplicons was used to profile the fungal communities. The fungal communities were predominantly composed of Basidiomycota (55% of reads) and Ascomycota (35%), with the orders Thelephorales (24%), Agaricales (13.8%), Pezizales (12.6%) and Sebacinales (11.3%) accounting for most of the reads. Plants from the same site or region had more similar fungal communities to one another than plants from other sites or regions, and sites clustered together along a weak latitudinal gradient. Furthermore, a decrease in per-plant OTU richness with increasing latitude was observed. However, no statistically significant spatial autocorrelation between sites was detected, suggesting that environmental filtering, not dispersal limitation, causes the observed patterns. Our analyses suggest that while latitudinal patterns in community composition and richness might reflect bioclimatic influences at global spatial scales, at the smaller spatial scale of the Svalbard archipelago, these changes more likely reflect varied bedrock composition and associated edaphic factors. The need for further studies focusing on identifying those specific bioclimatic and edaphic factors structuring root-associated fungal community composition at both global and local scales is emphasized., (© 2013 John Wiley & Sons Ltd.)

In High Arctic ecosystems, plant growth and reproduction are limited by low soil moisture and nutrient availability, low soil and air temperatures, and a short growing season. Mycorrhizal associations facilitate plant nutrient acquisition and water uptake and may therefore be particularly ecologically important in nutrition-poor and dry environments, such as parts of the Arctic. Similarly, endophytic root associates are thought to play a protective role, increasing plants' stress tolerance, and likely have an important ecosystem function. Despite the importance of these root-associated fungi, little is known about their host specificity in the Arctic. We investigated the host specificity of root-associated fungi in the common, widely distributed arctic plant species Bistorta vivipara, Salix polaris and Dryas octopetala in the High Arctic archipelago Svalbard. High-throughput sequencing of the internal transcribed spacer 1 (ITS1) amplified from whole root systems generated no evidence of host specificity and no spatial autocorrelation within two 3 m × 3 m sample plots. The lack of spatial structure at small spatial scales indicates that Common Mycelial Networks (CMNs) are rare in marginal arctic environments. Moreover, no significant differences in fungal OTU richness were observed across the three plant species, although their root system characteristics (size, biomass) differed considerably. Reasons for lack of host specificity could be that association with generalist fungi may allow arctic plants to more rapidly and easily colonize newly available habitats, and it may be favourable to establish symbiotic relationships with fungi possessing different physiological attributes., (© 2013 John Wiley & Sons Ltd.)

Even in cases in which geographic isolation appears to have driven the speciation of regional endemics, range shifts during the Pleistocene climatic oscillations may also have influenced their evolutionary history. Elucidating speciation history can provide novel insights into evolutionary dynamics following climatic oscillations. We demonstrated a sister relationship between the Japanese alpine endemic Cardamine nipponica and the currently allopatric, widespread arctic-alpine Cardamine bellidifolia (Brassicaceae) based on internal transcribed spacer (ITS) sequences and 10 other nuclear genes. Speciation history was inferred using demographic parameters under the isolation with migration model. The estimated demographic parameters showed that the population size of C. nipponica was similar to that of C. bellidifolia and that gene flow occurred exclusively from C. nipponica to C. bellidifolia after speciation. The inferred speciation history, which included gene flow, suggests that geographic barriers between the peripheral C. nipponica and the widespread C. bellidifolia were reduced during the Pleistocene. The asymmetric introgression implies that genetic isolation may have been involved in the speciation of C. nipponica. Our results suggest that even currently allopatric species may not have diverged solely under geographic isolation, and that their evolutionary history may have been influenced by Pleistocene range dynamics., (© 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.)

Background: Dryas octopetala is a widespread dwarf shrub in alpine and arctic regions that forms ectomycorrhizal (ECM) symbiotic relationships with fungi. In this study we investigated the fungal communities associated with roots of D. octopetala in alpine sites in Norway and in the High Arctic on Svalbard, where we aimed to reveal whether the fungal diversity and species composition varied across the Alpine and Arctic regions. The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was used to identify the fungal communities from bulk root samples obtained from 24 plants., Results: A total of 137 operational taxonomic units (OTUs) were detected (using 97% similarity cut off during sequence clustering) and well-known ECM genera such as Cenococcum, Cortinarius, Hebeloma, Inocybe and Tomentella occurred frequently. There was no decrease in fungal diversity with increasing latitude. The overall spatial heterogeneity was high, but a weak geographical structuring of the composition of OTUs in the root systems was observed. Calculated species accumulation curves did not level off., Conclusions: This study indicates that the diversity of fungi associated with D. octopetala does not decrease in high latitude arctic regions, which contrasts observations made in a wide spectrum of other organism groups. A high degree of patchiness was observed across root systems, but the fungal communities were nevertheless weakly spatially structured. Non-asymptotical species accumulation curves and the occurrence of a high number of singletons indicated that only a small fraction of the fungal diversity was detected.