Principal role of fungi in soil carbon stabilization during early pedogenesis in the high Arctic.

Climate warming is causing widespread deglaciation and pioneer soil formation over glacial deposits. Melting glaciers expose rocky terrain and glacial till sediment that is relatively low in biomass, oligotrophic, and depleted in nutrients. Following initial colonization by microorganisms, glacial till sediments accumulate organic carbon and nutrients over time. However, the mechanisms driving soil nutrient stabilization during early pedogenesis after glacial retreat remain unclear. Here, we traced amino acid uptake by microorganisms in recently deglaciated high-Arctic soils and show that fungi play a critical role in the initial stabilization of the assimilated carbon. Pioneer basidiomycete yeasts were among the predominant taxa responsible for carbon assimilation, which were associated with overall high amino acid use efficiency and reduced respiration. In intermediate- and late-stage soils, lichenized ascomycete fungi were prevalent, but bacteria increasingly dominated amino acid assimilation, with substantially decreased fungal:bacterial amino acid assimilation ratios and increased respiration. Together, these findings demonstrate that fungi are important drivers of pedogenesis in high-Arctic ecosystems that are currently subject to widespread deglaciation from global warming.

Description of antibiotic-producing novel bacteria Paraburkholderia antibiotica sp. nov. and Paraburkholderia polaris sp. nov.

Two white colony-forming, Gram-stain-negative, non-sporulating and motile bacteria, designated G-4-1-8T and RP-4-7T, were isolated from forest soil and Arctic soil, respectively. Both strains showed antimicrobial activity against Gram-negative pathogens (Pseudomonas aeruginosa and Escherichia coli) and could grow at a pH range of pH 4.0-11.0 (optimum, pH 7.0-9.0). Phylogenetic analyses based on their 16S rRNA gene sequences indicated that strains G-4-1-8T and RP-4-7T formed a lineage within the family Burkholderiaceae and were clustered as members of the genus Paraburkholderia. Strain G-4-1-8T showed the highest 16S rRNA sequence similarity to Paraburkholderia monticola JC2948T (98.1 %), while strain RP-4-7T showed the highest similarity to Paraburkholderia metrosideri DNBP6-1T (98.8 %). The only respiratory quinone in both strains was ubiquinone Q-8. Their principal cellular fatty acids were C16 : 0, cyclo-C17 : 0, summed feature 3 (iso-C15 :0 2-OH and/or C16 :1 ω7c) and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). Their major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and an unidentified aminophospholipid. The DNA G+C content of strains G-4-1-8T and RP-4-7T were 63.7 and 61.3 mol%, respectively, while their genome lengths were 7.44 and 9.67 Mb, respectively. The genomes of both strains showed at least 12 putative biosynthetic gene clusters. The average nucleotide identity and in silico DNA-DNA hybridization relatedness values between both strains and most closely related Paraburkholderia species were below the species threshold values. Based on a polyphasic study, these isolated strains represent novel species belonging to the genus Paraburkholderia, for which the names Paraburkholderia antibiotica sp. nov. (G-4-1-8T= KACC 21617T=NBRC 114603T) and Paraburkholderia polaris sp. nov. (RP-4-7T=KACC 21621T=NBRC 114605T) are proposed.

Cold-shock gene cspC in the genome of Massilia polaris sp. nov. revealed cold-adaptation.

A straw coloured, motile and Gram-stain-negative bacterium, designated RP-1-19T was isolated from soil of Arctic station, Svalbard, Norway. Based on the phylogenetic analysis of its 16S rRNA gene sequence, strain RP-1-19T formed a lineage within the family Oxalobacteraceae and clustered together within the genus Massilia. The closest members were M. violaceinigra B2T (98.6% sequence similarity), M. eurypsychrophilia JCM 30074T (98.3%) and M. atriviolacea SODT (98.1%). The only respiratory quinone was ubiquinone-8. The principal cellular fatty acids were summed feature 3 (iso-C15:0 2-OH/C16:1ω7c) and C16:0. The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol. The DNA G + C content of the type strain was 63.2%. The average nucleotide identity and in silico DNA-DNA hybridization values between strain RP-1-19T and closest members were ≤ 80 and 23.2%, respectively. The genome was 4,522,469 bp long with 30 scaffolds and 4076 protein-coding genes. The genome showed eight putative biosynthetic gene clusters responsible for various secondary metabolites. Genome analysis revealed the presence of cold-shock proteins CspA and CspC. Presence of cspA and cspC genes in the genome manifest ecophysiology of strain RP-1-19T that may help in cold-adaptation. Based on these data, strain RP-1-19T represents a novel species in the genus Massilia, for which the name Massilia polaris sp. nov. is proposed. The type strain is RP-1-19T (= KACC 21619T = NBRC 114359T).

Cryptogams signify key transitions of bacteria and fungi in Arctic sand dune succession.

Primary succession models focus on aboveground vascular plants. However, the prevalence of mosses and lichens, that is cryptogams, suggests they play a role in soil successions. Here, we explore whether effects of cryptogams on belowground microbes can facilitate progressive shifts in sand dune succession. We linked aboveground vegetation, belowground bacterial and fungal communities, and soil chemical properties in six successional stages in Arctic inland sand dunes: bare sand, grass, moss, lichen, ericoid heath and mountain birch forest. Compared with the bare sand and grass stages, microbial biomass and the proportion of fungi increased in the moss stage, and later stage microbial groups appeared despite the absence of their host plants. Microbial communities of the lichen stage resembled the communities in the vascular plant stages. Bacterial communities correlated better with soil chemical variables than with vegetation and vice versa for fungal communities. The correlation of fungi with vegetation increased with vascular vegetation. Distinct bacterial and fungal patterns of biomass, richness and plant-microbe interactions showed that the aboveground vegetation change structured the bacterial and fungal community differently. The asynchrony of aboveground vs belowground changes suggests that cryptogams can drive succession towards vascular plant dominance through microbially mediated facilitation in eroded Arctic soil.

Nine novel psychrotolerant species of the genus Pedobacter isolated from Arctic soil with potential antioxidant activities.

Fifteen isolates of the genus Pedobacter were obtained from Arctic soil samples. All isolates were Gram-stain-negative and rod-shaped. Cells were strictly aerobic, psychrotolerant and grew optimally at 15-20 °C. Phylogenetic analysis based on 16S rRNA gene sequences revealed that all the isolated strains formed a lineage within the family Sphingobacteriaceae and clustered as members of the genus Pedobacter. The sole respiratory quinone was MK-7 and the major polar lipid was phosphatidylethanolamine. The major cellular fatty acids were summed feature 3 (iso-C15 : 02-OH/C16 : 1ω7c/ω6c), iso-C15 : 0 and iso-C17 : 0 3-OH. The DNA G+C content of the novel strains was 33.9-41.8 mol%. In addition, the average nucleotide identity and in silico DNA-DNA hybridization relatedness values between the novel type strains and phylogenetically related type strains were below the threshold values used for species delineation. Based on genomic, chemotaxonomic, phenotypic, phylogenetic and phylogenomic analyses, the isolated strains represent novel species in the genus Pedobacter, for which the names Pedobacter cryotolerans sp. nov. (type strain AR-2-6T=KEMB 9005-717T=KACC 19998T=NBRC 113826T), Pedobacter cryophilus sp. nov. (type strain AR-3-17T=KEMB 9005-718T=KACC 19999T=NBRC 113827T), Pedobacter frigiditerrae sp. nov. (type strain RP-1-13T=KEMB 9005-720T=KACC 21147T=NBRC 113829T), Pedobacter psychroterrae sp. nov. (type strain RP-1-14T=KEMB 9005-721T=KACC 21148T=NBRC 113830T), Pedobacter hiemivivus sp. nov. (type strain RP-3-8T=KEMB 9005-724T=KACC 21152T=NBRC 113833T), Pedobacter frigidisoli sp. nov. (type strain RP-3-11T=KEMB 9005-725T=KACC 21153T=NBRC 113927T), Pedobacter frigoris sp. nov. (type strain RP-3-15T=KEMB 9005-726T=KACC 21154T=NBRC 113834T), Pedobacter psychrodurus sp. nov. (type strain RP-3-21T=KEMB 9005-728T=KACC 21156T=NBRC 113835T) and Pedobacter polaris sp. nov. (type strain RP-3-22T=KEMB 9005-729T=KACC 21157T=NBRC 113836T) are proposed.

Dyadobacter psychrotolerans sp. nov. and Dyadobacter frigoris sp. nov., two novel psychrotolerant members of the family Cytophagaceae isolated from Arctic soil.

Four strains of bacteria designated as AR-3-6T, AT-3-1, AR-3-8T and AR-3-15 were isolated from Arctic soil. Cells were aerobic, Gram-staining-negative, non-motile, non-spore-forming, rod-shaped and yellow-pigmented. Flexirubin-type pigments were present in all strains. All strains tolerated 2 % of NaCl and were psychrotolerant. A phylogenetic analysis based on its 16S rRNA gene sequence revealed that these strains formed a lineage within the family Cytophagaceae that were distinct from various members of the genus Dyadobacter. The closest member of strain AR-3-6T was D. koreensis DSM 19938T (97.2 % sequence similarity) and AR-3-8T was D. hamtensis HHS 11T (97.9 %). The predominant respiratory quinone was menaqinone-7. The major polar lipid was phosphatidylethanolamine. The major cellular fatty acids were summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0, C16 : 1ω5c and iso-C17 : 0 3-OH. The DNA G+C content of strains ranges from 40.1 to 42.1 mol%. On the basis of phenotypic, genotypic, chemotaxonomic and phylogenetic analysis, both strains AR-3-6T and AR-3-8T represent a novel member in the genus Dyadobacter, for which the name Dyadobacter psychrotolerans sp. nov. and Dyadobacter frigoris sp. nov. are proposed, respectively. The type strain of Dyadobacter psychrotolerans is AR-3-6T (=KEMB 9005-743T=KACC 21172T=NBRC 113790T) and type strain of Dyadobacter frigoris is AR-3-8T (=KEMB 9005-744T= KACC 21173T=NBRC 113791T).

Flavobacterium sandaracinum sp. nov., Flavobacterium caseinilyticum sp. nov., and Flavobacterium hiemivividum sp. nov., novel psychrophilic bacteria isolated from Arctic soil.

This study presents taxonomic description of strains LB-D12T, AT-3-2T, AT-3-7, and TSA-D2T isolated from Arctic soil. All strains were psychrophilic, Gram-stain-negative, aerobic, non-motile, and rod-shaped. Phylogenetic analysis showed that these strains belonged to the genus Flavobacterium. Strains LB-D12T, AT-3-2T and AT-3-7 were closest to Flavobacterium psychrolimnae LMG 22018T (98.5-98.8% sequence similarity). Strain TSA-D2T was closest to Flavobacterium degerlachei DSM 15718T (98.3 % sequence similarity). These strains shared common chemotaxonomic features comprising MK-6 as a sole quinone, phosphatidylethanolamine as the principal polar lipid, and summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c), iso-C16 : 0 3-OH, C15 : 1ω6c, iso-C16 : 0, and anteiso-C15 : 0 as the main fatty acids. The ANI and dDDH values between these novel isolates and their closest relatives were below the cut-off values of 95 and 70 %, respectively used for species demarcation. The DNA G+C content of all strains ranged from 34.2 to 34.6 mol%. The obtained polyphasic taxonomic data suggested that the isolated strains represent novel species within the genus Flavobacterium, for which the names Flavobacterium sandaracinum sp. nov. (type strain LB-D12T=KEMB 9005-737T=KACC 21180T=NBRC 113784T), Flavobacterium caseinilyticum sp. nov. (type strain AT-3-2T=KEMB 9005-738T=KACC 21176T=NBRC 113785T), and Flavobacterium hiemivividum sp. nov. (type strain TSA-D2T=KEMB 9005-741T=KACC 21179T=NBRC 113788T) are proposed.

Hymenobacter polaris sp. nov., a psychrotolerant bacterium isolated from an Arctic station.

A pink-pigmented, non-motile, Gram-stain-negative, rod-shaped bacterium, designated RP-2-7T, was obtained from soil sampled at the Arctic station, Spitsbergen, Svalbard, Norway. Cells were strictly aerobic, psychrotolerant, grew optimally at 15-20 °C and hydrolysed CM-cellulose. Phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain RP-2-7T formed a lineage within the family Hymenobacteraceae and clustered with members of the genus Hymenobacter. Its closest relative was Hymenobacter marinus KJ035T (97.6 % sequence similarity). The sequence similarities to other strains were ≤96.9 %. The principal respiratory quinone was MK-7 and the major polar lipids were phosphatidylethanolamine and an unidentified aminophospholipid. The predominant cellular fatty acids were summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), anteiso-C15 : 0, iso-C15 : 0, C16 : 1 ω5c and summed featured 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B). The DNA G+C content was 62.8 mol%. In addition, the average nucleotide identity and in silico DNA-DNA hybridization relatedness values between strain RP-2-7T and closely related strains were lower than species demarcation thresholds. Based on the resuls of genomic, chemotaxonomic, phenotypic and phylogenetic analyses, strain RP-2-7T represents novel species in the genus Hymenobacter, for which the name Hymenobacter polaris sp. nov. is proposed. The type strain is RP-2-7T (=KACC 21670T=NBRC 114391T).

Flavobacterium cellulosilyticum sp. nov., a novel psychrophilic bacterium isolated from Arctic soil.

A novel psychrophilic, light-yellow-coloured, aerobic, Gram-stain-negative, rod-shaped, non-motile bacterium, designated strain AR-3-4T was isolated from a sample of Arctic soil. Strain AR-3-4T grew at 0-25 °C, pH 6.0-9.0 and 0-1.0 % (w/v) NaCl concentration. The 16S rRNA gene sequence analysis showed that strain AR-3-4T belonged to the genus Flavobacterium, with nearest phylogenetic neighbour being Flavobacterium fluvii H7T (97.5 % sequence similarity). The strain comprised phosphatidylethanolamine as the main polar lipid, MK-6 as predominant respiratory quinone, and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), anteiso-C15 : 0 and iso-C15 : 0 as the major fatty acids. The average nucleotide identity and in silico DNA-DNA hybridization values between strain AR-3-4T and closest members were below the threshold values of 95 % and 70 %, respectively. The DNA G+C content was 33.0 mol%. Based on the polyphasic taxonomic data, the novel species Flavobacterium cellulosilyticum sp. nov. is proposed with the type strain AR-3-4T (=KEMB 9005-740T=KACC 21171T=NBRC 113787T).

Flavobacterium dasani sp. nov., a psychrotolerant bacterium isolated from Arctic soil.

A novel yellow-colored, Gram-stain-negative, aerobic, non-motile, catalase- and oxidase-positive, and rod-shaped psychrotolerant bacterium, designated strain PLR-18-3T, was isolated from Arctic soil and was subjected to polyphasic taxonomic study. Cells were able to grow at 0-30 °C, pH 6.0-10.5, and 0-3.0% (w/v) NaCl concentration. Based on the 16S rRNA gene sequence analysis, this Arctic strain belonged to the genus Flavobacterium, with the closest neighbor being Flavobacterium noncentrifugens R-HLS-17T (96.2% sequence similarity). The strain contained MK-6 as a sole respiratory quinone, phosphatidylethanolamine as the major polar lipid, and summed feature 3 (C16:1ω7c and/or C16:1ω6c), iso-C15:0, iso-C15:0 G, iso-C17:0 3-OH, iso-C15:0 3-OH, anteiso-C15:0, and summed feature 9 (iso-C17:1ω9c and/or C16:010-methyl) as the predominant fatty acids. The DNA G + C content was 37.9 mol%. On the basis of polyphasic data, strain PLR-18-3T represents a novel species of the genus Flavobacterium, for which the name Flavobacterium dasani sp. nov. is proposed. The type strain is PLR-18-3T (=KEMB 9005-713T=KACC 19627T=NBRC 113347T).

Description of Sphingobium psychrophilum sp. nov., a cold-adapted bacterium isolated from Arctic soil.

A yellow-coloured, Gram-stain-negative, non-sporulating, psychrotolerant and motile bacterium, designated AR-3-1T, was isolated from the Arctic soil of Cambridge Bay, Nunavut, Canada. Strain AR-3-1T could grow at 4-32 °C and pH 5.0- 11.0. Phylogenetic analysis based on its 16S rRNA gene sequence indicated that strain AR-3-1T formed a lineage within the family Sphingomonadaceae and clustered as a member of the genus Sphingobium. The closest members within this genus were Sphingobium cupriresistens CU4T (98.1 % sequence similarity), Sphingobium vermicomposti VC-230T (97.6 %) and Sphingobium lactosutens DS20T (97.5 %). The only respiratory quinone was the ubiquinone Q-10. Spermidine was the predominant polyamine. The principal cellular fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c), summed feature 3 (iso-C15  : 0 2-OH and/or C16  : 1 ω7c), C16 : 0 and C14 : 0 2-OH. The major polar lipids were phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, sphingoglycolipid and phosphoglycolipid. The DNA G+C content was 63.1 %. The average nucleotide identity and in silico DNA-DNA hybridization relatedness values between strain AR-3-1T and its most closely related genus members were ≤89.6 and 39.6 %, respectively. The genome was 5 162 327 bp long, with 83 scaffolds and 4824 protein-coding genes. The genome showed six putative biosynthetic gene clusters responsible for various secondary metabolites. Based on this polyphasic study, strain AR-3-1T represents a novel species within the genus Sphingobium, for which the name Sphingobium psychrophilum sp. nov. is proposed. The type strain is AR-3-1T (=KACC 21613T=NBRC 114604T).

Glaciihabitans arcticus sp. nov., a psychrotolerant bacterium isolated from Arctic soil.

A non-motile, Gram-stain-positive, rod-shaped bacterium, designated RP-3-7T, was isolated from soil sampled at the Arctic region in Cambridge Bay, NU, Canada. Cells were strictly aerobic, non-spore-forming, catalase-positive and oxidase-positive. Colonies on Reasoner's 2A agar plates were pale yellow-coloured. Strain RP-3-7T was psychrotolerant and grew optimally at 15-20 °C. Strain RP-3-7T assimilated d-glucose, d-mannitol, l-arabinose and l-proline; tolerated only 0.5 % NaCl (w/v). Phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain RP-3-7T formed a lineage within the family Microbacteriaceae and clustered with members of the genus Glaciihabitans. The closest member was Glaciihabitans tibetensis MP203T (98.26 % sequence similarity). The major respiratory quinone was MK-10. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unidentified glycolipid. The major cellular fatty acids were anteiso-C15 : 0, iso-C16 : 0, anteiso-C17 : 0 and anteiso-C15 : 1 A. The diagnostic amino acid was 2,4-diaminobutyric acid and whole-cell sugars were xylose, rhamnose and mannose. The DNA G+C content of strain RP-3-7T was 66.9 mol%. The average nucleotide identity and in silico DNA-DNA relatedness values between strain RP-3-7T and Glaciihabitans tibetensis MP203T were 73.79 and 20.1 %, respectively. Based on the polyphasic, genomic and phylogenetic data, strain RP-3-7T represents a novel species of the genus Glaciihabitans, for which the name Glaciihabitans arcticus sp. nov. is proposed. The type strain is RP-3-7T (=KEMB 9005-731T=KACC 21151T=NBRC 113769T).

Long-term experimental warming alters community composition of ascomycetes in Alaskan moist and dry arctic tundra.

Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long-term (18 years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss-associated fungi decreased with warming, while the proportion of several plant and insect pathogens and saprotrophic species was higher in the warming treatment. The observed alterations in both taxonomic and ecological groups of ascomycetes are discussed in relation to previously reported warming-induced shifts in arctic plant communities, including decline in lichens and bryophytes and increase in coverage and biomass of shrubs.

Depth-specific distribution of bacterial MAGs in permafrost active layer in Ny Ålesund, Svalbard (79°N).

Arctic soil microbial communities may shift with increasing temperatures and water availability from climate change. We examined temperature and volumetric liquid water content (VWC) in the upper 80 cm of permafrost-affected soil over 2 years (2018-2019) at the Bayelva monitoring station, Ny Ålesund, Svalbard. We show VWC increases with depth, whereas in situ temperature is more stable vertically, ranging from -5°C to 5 °C seasonally. Prokaryotic metagenome-assembled genomes (MAGs) were obtained at 2-4 cm vertical resolution collected while frozen in April 2018 and at 10 cm vertical resolution collected while thawed in September 2019. The most abundant MAGs were Acidobacteriota, Actinomycetota, and Chloroflexota. Actinomycetota and Chloroflexota increase with depth, while Acidobacteriota classes Thermoanaerobaculia Gp7-AA8, Blastocatellia UBA7656, and Vicinamibacteria Vicinamibacterales are found above 6 cm, below 6 cm, and below 20 cm, respectively. All MAGs have diverse carbon-degrading genes, and Actinomycetota and Chloroflexota have autotrophic genes. Genes encoding ß -glucosidase, N-acetyl-ß-D-glucosaminidase, and xylosidase increase with depth, indicating a greater potential for organic matter degradation with higher VWC. Acidobacteriota dominate the top 6 cm with their classes segregating by depth, whereas Actinomycetota and Chloroflexota dominate below ∼6 cm. This suggests that Acidobacteriota classes adapt to lower VWC at the surface, while Actinomycetota and Chloroflexota persist below 6 cm with higher VWC. This indicates that VWC may be as important as temperature in microbial climate change responses in Arctic mineral soils. Here we describe MAG-based Seqcode type species in the Acidobacteriota, Onstottus arcticum, Onstottus frigus, and Gilichinskyi gelida and in the Actinobacteriota, Mayfieldus profundus.

Soil microorganisms and methane emissions in response to short-term warming field incubation in Svalbard.

Introduction: Global warming is caused by greenhouse gases (GHGs). It has been found that the release of methane (CH4) from Arctic permafrost, soil, ocean, and sediment is closely related to microbial composition and soil factors resulting from warming over several months or years. However, it is unclear for how long continuous warming due to global warming affects the microbial composition and GHG release from soils along Arctic glacial meltwater rivers. Methods: In this study, the soil upstream of the glacial meltwater river (GR) and the estuary (GR-0) in Svalbard, with strong soil heterogeneity, was subjected to short-term field incubation at 2°C (in situ temperature), 10°C, and 20°C. The incubation was carried out under anoxic conditions and lasted for few days. Bacterial composition and CH4 production potential were determined based on high-throughput sequencing and physiochemical property measurements. Results: Our results showed no significant differences in bacterial 16S rRNA gene copy number, bacterial composition, and methanogenic potential, as measured by mcrA gene copy number and CH4 concentration, during a 7- and 13-day warming field incubation with increasing temperatures, respectively. The CH4 concentration at the GR site was higher than that at the GR-0 site, while the mcrA gene was lower at the GR site than that at the GR-0 site. Discussion: Based on the warming field incubation, our results indicate that short-term warming, which is measured in days, affects soil microbial composition and CH4 concentration less than the spatial scale, highlighting the importance of warming time in influencing CH4 release from soil. In summary, our research implied that microbial composition and CH4 emissions in soil warming do not increase in the first several days, but site specificity is more important. However, emissions will gradually increase first and then decrease as warming time increases over the long term. These results are important for understanding and exploring the GHG emission fluxes of high-latitude ecosystems under global warming.

Arctic soil CO2 release during freeze-thaw cycles modulated by silicon and calcium.

Arctic soils are the largest pool of soil organic carbon worldwide. Temperatures in the Arctic have risen faster than the global average during the last decades, decreasing annual freezing days and increasing the number of freeze-thaw cycles (temperature oscillations passing through zero degrees) per year as the temperature is expected to fluctuate more around 0 °C. At the same time, proceeding deepening of seasonal thaw may increase silicon (Si) and calcium (Ca) concentrations in the active layer of Arctic soils as the concentrations in the thawing permafrost layer might be higher depending on location. We analyzed the importance of freeze-thaw cycles for Arctic soil CO2 fluxes. Furthermore, we tested how Si (mobilizing organic C) and Ca (immobilizing organic C) interfere with the soil CO2 fluxes in the context of freeze-thaw cycles. Our results show that with each freeze-thaw cycle the CO2 fluxes from the Arctic soils decreased. Our data revealed a considerable CO2 emission below 0 °C. We also show that pronounced differences emerge in Arctic soil CO2 fluxes with Si increasing and Ca decreasing CO2 fluxes. Furthermore, we show that both Si and Ca concentrations in Arctic soils are central controls on Arctic soil CO2 release, with Si increasing Arctic soil CO2 release especially when temperatures are just below 0 °C. Our findings could provide an important constraint on soil CO2 emissions upon soil thaw, as well as on the greenhouse gas budget of high latitudes. Thus we call for work improving understanding of freeze-thaw cycles as well as the effect of Ca and Si on carbon fluxes, as well as for increased consideration of those factors in wide-scale assessments of carbon fluxes in the high latitudes.

Carbon Emission and Biodiversity of Arctic Soil Microbial Communities of the Novaya Zemlya and Franz Josef Land Archipelagos.

Cryogenic soils are the most important terrestrial carbon reservoir on the planet. However, the relationship between soil microbial diversity and CO2 emission by cryogenic soils is poorly studied. This is especially important in the context of rising temperatures in the high Arctic which can lead to the activation of microbial processes in soils and an increase in carbon input from cryogenic soils into the atmosphere. Here, using high-throughput sequencing of 16S rRNA gene amplicons, we analyzed microbial community composition and diversity metrics in relation to soil carbon dioxide emission, water-extractable organic carbon and microbial biomass carbon in the soils of the Barents Sea archipelagos, Novaya Zemlya and Franz Josef Land. It was found that the highest diversity and CO2 emission were observed on the Hooker and Heiss Islands of the Franz Josef Land archipelago, while the diversity and CO2 emission levels were lower on Novaya Zemlya. Soil moisture and temperature were the main parameters influencing the composition of soil microbial communities on both archipelagos. The data obtained show that CO2 emission levels and community diversity on the studied islands are influenced mostly by a number of local factors, such as soil moisture, microclimatic conditions, different patterns of vegetation and fecal input from animals such as reindeer.

Diverse viromes in polar regions: A retrospective study of metagenomic data from Antarctic animal feces and Arctic frozen soil in 2012-2014.

Antarctica and the Arctic are the coldest places, containing a high diversity of microorganisms, including viruses, which are important components of polar ecosystems. However, owing to the difficulties in obtaining access to animal and environmental samples, the current knowledge of viromes in polar regions is still limited. To better understand polar viromes, this study performed a retrospective analysis using metagenomic sequencing data of animal feces from Antarctica and frozen soil from the Arctic collected during 2012-2014. The results reveal diverse communities of DNA and RNA viruses from at least 23 families from Antarctic animal feces and 16 families from Arctic soils. Although the viral communities from Antarctica and the Arctic show a large diversity, they have genetic similarities with known viruses from different ecosystems and organisms with similar viral proteins. Phylogenetic analysis of Microviridae, Parvoviridae, and Larvidaviridae was further performed, and complete genomic sequences of two novel circular replication-associated protein (rep)-encoding single-stranded (CRESS) DNA viruses closely related to Circoviridae were identified. These results reveal the high diversity, complexity, and novelty of viral communities from polar regions, and suggested the genetic similarity and functional correlations of viromes between the Antarctica and Arctic. Variations in viral families in Arctic soils, Arctic freshwater, and Antarctic soils are discussed. These findings improve our understanding of polar viromes and suggest the importance of performing follow-up in-depth investigations of animal and environmental samples from Antarctica and the Arctic, which would reveal the substantial role of these viruses in the global viral community.

Response of carbon and microbial properties to risk elements pollution in arctic soils.

A 180-day incubation study was conducted to evaluate the effects of risk elements (REs) on organic carbon use and microbial activities in organic soils in the Arctic during the summer snowmelt period. Soils were artificially spiked with Cd, Pb, Cr, Ni, Cu, As, and a combination of these REs according to the levels measured in Arctic soils from REs-polluted industrial sites. During the incubation period, microbial activities and microbial biomass carbon (MBC) formation were inhibited, and microbial quotient (qCO2) values were relatively high in the spiked soils indicating that more energy was used by microbes for maintenance under REs stress. Meanwhile, microbial metabolism was significantly restrained. Microbial Specific phospholipid fatty acids (PLFAs) were reduced in RE spiked soils relative to the control, especially in the As- and multi-RE-spiked soils. The abundance of both fungi and bacteria was reduced in response to RE amendments by 14-24% and 1-55%, respectively. PLFA biomarkers indicated a shift in soil microbial community structure and activities influenced by REs, consequently having a negative effect on soil organic carbon degradation. This study addresses the knowledge gap regarding the alternation of biochemical reactions in Arctic soils under anthropogenic REs with relevant contamination levels.

Biogeographical patterns in soil bacterial communities across the Arctic region.

The considerable microbial diversity of soils and key role in biogeochemical cycling have led to growing interest in their global distribution and the impact that environmental change might have at the regional level. In the broadest study of Arctic soil bacterial communities to date, we used high-throughput DNA sequencing to investigate the bacterial diversity from 200 independent Arctic soil samples from 43 sites. We quantified the impact of spatial and environmental factors on bacterial community structure using variation partitioning analysis, illustrating a nonrandom distribution across the region. pH was confirmed as the key environmental driver structuring Arctic soil bacterial communities, while total organic carbon (TOC), moisture and conductivity were shown to have little effect. Specialist taxa were more abundant in acidic and alkaline soils while generalist taxa were more abundant in acidoneutral soils. Of the 48 147 bacterial taxa, a core microbiome composed of only 13 taxa that were ubiquitously distributed and present within 95% of samples was identified, illustrating the high potential for endemism in the region. Overall, our results demonstrate the importance of spatial and edaphic factors on the structure of Arctic soil bacterial communities.