Arctic Soils Research Articles

Changes in the Soil-Plant Cover of the High Arctic of Eastern Siberia

Investigations of changes in the soil and plant covers is necessary when designing technical objects—gas and oil pipelines, highways, and power lines—in order to avoid the adverse effects of these activities and to preserve vulnerable northern ecosystems. Recent changes in the soil–plant cover of the High Arctic of Eastern Siberia are directed towards its higher complexity. Chaotic bare stone debris evolve into stony polygons with “soil embryos” and patchy vegetation. Recently deglaciated areas are locally overgrown with plants on weakly developed soils of the initial stage of pedogenesis and then evolve towards the stage of mosaic plant cover with tonguing (glossic) soils. At the next stage, soil–plant complexes are formed with a continuous plant cover on soddy arctic soils. Melt water of glaciers and snow fields saturate the sediments and may induce their textural differentiation. Soil and plant cover changes in the areas with ice wedges have their own specificity. Ice wedges are typical of floodplains, where they form tetragonal complexes of moss or moss–grass tundra with gleyzems and peat soils on tops of the wedges. After the cessation of floods, ice wedges tend to degrade, and small lakes are formed in their places. Bogged tetragons are replaced by the mesophilic forb–grass tundra with gleyic soils. Under conditions of good drainage, this stage is followed by the stage of baydzharakh terrain. When the baydzharakhs are destroyed, a hummocky grass–forb tundra with soddy tundra soils appears.

Functional and Structural Responses of Arctic and Alpine Soil Prokaryotic and Fungal Communities Under Freeze-Thaw Cycles of Different Frequencies.

Ongoing climate change involves increasing snow scarcity, which results in more frequent freeze-thaw cycles (FTCs) in polar and alpine soils. Although repeated FTCs have been shown to alter the structure and functions of soil microbial communities, a thorough understanding on the influence of FTCs frequency on polar and especially alpine soil microbiomes is still elusive. Here, we investigated the impact of repeated weekly vs. daily FTC frequencies on the structure and functions of prokaryotic and fungal communities from north- and south-exposed soils from two mountain ridges, one in the Arctic and one in the High-Alps. FTCs affected prokaryotic communities more strongly than fungal communities, where mainly cold-tolerant and opportunistic fungi (e.g., Mrakia, Mortierella) were responsive. Prokaryotic communities were more affected by weekly FTCs than by daily FTCs. Daily FTCs favored fast-growing bacteria (e.g., Arthrobacter), while oligotrophic and largely uncultured taxa (e.g., Verrucomicrobia) benefited from weekly FTCs. FTCs negatively affected microbial respiration but had minor impacts on C-, N- and P-acquiring enzymatic activities. Plausible pre-adaptation of the microbial communities to naturally occurring frequent FTCs at their site of origin did not show a clear influence on the microbial responses to the tested FTCs. Altogether, our study provides an integrative overview on potential structural and functional changes of soil microbial communities in polar and alpine regions in response to the projected increase in FTCs; therefore advancing our understanding on the impact of climate change in these rapidly changing ecosystems.

Mimicking climate warming effects on Alaskan soil microbial communities via gradual temperature increase

Climate change can trigger shifts in community structure and may therefore pose a severe threat to soil microbial communities, especially in high northern latitudes such as the Arctic. Arctic soils are covered by snow and ice throughout most of the year. This insulation shields them from high temperature variability and low surface temperatures. If this protective layer thaws, these soils are predicted to warm up at 1.5x to 4x the rate of other terrestrial biomes. In this study, we sampled arctic soils from sites with different elevations in Alaska, incubated them for 5 months with a simulated, gradual or abrupt temperature increase of +5 °C, and compared bacterial and fungal community compositions after the incubation. We hypothesized that the microbial communities would not significantly change with a gradual temperature treatment, whereas an abrupt temperature increase would decrease microbial diversity and shift community composition. The only differences in community composition that we observed were, however, related to the two elevations. The abrupt and gradual temperature increase treatments did not change the microbial community composition as compared to the control indicating resistance of the microbial community to changes in temperature. This points to the potential importance of microbial dormancy and resting stages in the formation of a “buffer” against elevated temperatures. Microbial resting stages might heavily contribute to microbial biomass and thus drive the responsiveness of arctic ecosystems to climate change.

Pojemność wodna i właściwości gleb rosyjskiej Arktyki (na przykładzie delty rzeki Leny i Półwyspu Jamalskiego)

Pojemność wodna i właściwości gleb rosyjskiej Arktyki (na przykładzie delty rzeki Leny i Półwyspu Jamalskiego)

Tissue-Specific Dynamics in the Endophytic Bacterial Communities in Arctic Pioneer Plant Oxyria digyna.

The rapid developments in the next-generation sequencing methods in the recent years have provided a wealth of information on the community structures and functions of endophytic bacteria. However, the assembly processes of these communities in different plant tissues are still currently poorly understood, especially in wild plants in natural settings. The aim of this study was to compare the composition of endophytic bacterial communities in leaves and roots of arcto-alpine pioneer plant Oxyria digyna, and investigate, how plant tissue (leaf or root) or plant origin affect the community assembly. To address this, we planted micropropagated O. digyna plants with low bacterial load (bait plants) in experimental site with native O. digyna population, in the Low Arctic. The endophytic bacterial community structures in the leaves and roots of the bait plants were analyzed after one growing season and one year in the field, and compared to those of the wild plants growing at the same site. 16S rRNA gene targeted sequencing revealed that endophytic communities in the roots were more diverse than in the leaves, and the diversity in the bait plants increased in the field, and was highest in the wild plants. Both tissue type and plant group had strong impact on the endophytic bacterial community structures. Firmicutes were highly abundant in the leaf communities of both plant types. Proteobacteria and Bacteroidetes were more abundant in the roots, albeit with different relative abundances in different plant groups. The community structures in the bait plants changed in the field over time, and increasingly resembled the wild plant endophytic communities. This was due to the changes in the relative abundances of several bacterial taxa, as well as species acquisition in the field, but with no species turnover. Several OTUs that were acquired by the bait plants in the field and represent phosphate solubilizing and diazotrophic bacterial taxa, suggesting major role in nutrient acquisition of these bacteria for this nonmycorrhizal plant, thriving in the nutrient poor arctic soils.

Chitinimonas arctica sp. nov., isolated from Arctic tundra soil.

A Gram-stain-negative, rod-shaped, green-pigmented, aerobic and motile bacterium, strain R3-44T, was isolated from Arctic tundra soil. Stain R3-44T clustered closely with members of the genus Chitinimonas, which belongs to the family Burkholderiaceae, and showed the highest 16S rRNA sequence similarity to Chitinimonas naiadis AR2T (96.10%). Strain R3-44T grew optimally at pH 7.0, 28 °C and in the presence of 0-0.5 % (w/v) NaCl. The predominant respiratory isoprenoid quinone of strain R3-44T was identified as ubiquinone Q-8. The polar lipids consisted of phosphatidylglycerol, phosphatidylethanolamine, unidentified aminolipid and unidentified phospholipid. The main fatty acids were summed feature 3 (comprising C16 : 1 ω7c and/or C16 : 1 ω6c, 40.6 %) and C16 : 0 (29.3 %). The DNA G+C content of strain R3-44T was 60.8 mol%. On the basis of the evidence presented in this study, strain R3-44T represents a novel species of the genus Chitinimonas, for which the name Chitinimonas arctica sp. nov. is proposed, with the type strain R3-44T (=CCTCC AB 2010422T=KCTC 72602T).

Features of Transformation of Oil-contaminated Soils in Arctic Region

A study of the comparative characteristic of Yakutia´s frozen soils ability to remediation, when contaminated with oil, has been carried out. The samples of permafrost soils from the territories of the the Republic of Sakha (Yakutia), exposed to industrial pollution by oil and its products, with old periods of pollution (10 ÷ 12 years) were examined. Remediation was not carried out anywhere. In the soils of the western part of Yakutia, despite a high residual level of pollution (8.58%), signs of oxidative destruction of petroleum hydrocarbons are clearly visible (high content of resinous components (61.3%)), and almost complete transformation of acyclic hydrocarbons. In arctic soils, self-remediation processes occur at a significantly slower pace. In these soils the content of hydrocarbon fractions is still high (60.3-64.9%). There is no selectivity in the transformation processes of individual acyclic hydrocarbons. This suggests that the oxidative destruction of oil pollution in Arctic soils is mainly influenced by physical and chemical environmental factors, rather than microbiological oxidation. The low microbiological activity of hydrocarbon-oxidizing microorganisms in the Arctic soils indicates the need to develop special remediation measures to clean the soil from oil pollution

Arctic and tundra soils on the new digital soil map of Russia, 1 : 2.5 M scale

V.V. Dokuchaev Soil Science Institute has initiated a project on compilation of a new Digital Soil Map of Russia on the basis of the Soil Map of the Russian Federation (SMRF) 1 : 2.5 M scale (1988) revised and interpreted in ideology and nomenclature of the new substantive-genetic Classification System of Russian Soils (CSRS). The first stage implies the conversion of soil mapping units on the original map into the CSRS with a corresponding renaming of soils in the attribute database to the digitized version of the map for each soil polygon. During the second stage, a new digital model of the soil cover is developed with the use of digital soil mapping technologies, basic soil map, and new materials, including satellite images and digital elevation models. The legend section “Tundra Soils” contains 16 soil units forming their own areas or found in various combinations (soil complexes). As a result of the reclassification and careful analysis of each soil polygon, the soils of Arctic and Subarctic tundra have obtained a more detailed and differential representation on the new map, and their diagnostics based on the morphology of the profiles and major soil properties have been specified. The most significant changes in the initial content of the map concern the soils referred to as gley soils on the SMRF. A separate group of cryozemic soils has been specified. Weakly developed soils (petrozems, psammozems, and pelozems) and lithozems have been int r oduced on the map for the first time. Differential decisions are suggested for the soils of “spotty tundra” with sorted and nonsorted circles and for the soils of cryogenic fissures and cracks. The results of the study have made it possible to refine the diagnostics and nomenclature of soils in the CSRS.

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.

Natural attenuation of spilled crude oil by cold-adapted soil bacterial communities at a decommissioned High Arctic oil well site

Romulus C-42 is a decommissioned oil well on Ellesmere Island in the Canadian High Arctic, and is the northernmost well to have produced oil and gas anywhere in the world. The remote site has been untouched since a crude oil spill in 1972, offering a rare opportunity to examine natural attenuation in Arctic soils >40 years after a pollution event. Bacterial community composition in crude oil contaminated soils was significantly different from adjacent background soils. Two members of the genus Rhodanobacter (Alphaproteobacteria) were found consistently in contaminated soils, whereas two members of the genus Sphingomonas (Gammaproteobacteria) appeared opposite to each other, one consistently within the oil contaminated soil and the other consistently in non-oil contaminated soils. GC of soil hydrocarbon extracts revealed moderate levels of biodegradation relative to the original oil produced in 1972. Despite conditions permissive for bacterial activity (>0 °C) being limited to only a few months each year, natural attenuation by cold adapted soil microbial communities has taken place since the oil spill over 40 years ago. Rhodanobacter and Sphingomonas lineages are associated with contaminated and baseline conditions in this extreme environment, revealing the utility of bacterial diversity measurements for assessing long-term responses of Arctic soils to pollution. Originality-significance statementRomulus C-42, the northernmost onshore drilling well in the world, was decommissioned following a small crude oil spill in 1972. Soil bacterial diversity profiles obtained >40 years later revealed significant differences in oil contaminated soils relative to adjacent non-oil contaminated background soils, consistent with evidence for moderate biodegradation of spilled crude oil having taken place since 1972. The results indicate that microbial diversity profiling is an effective tool for assessing natural attenuation in remote High Arctic soils with a history of oil pollution.

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.

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.

A dielectric model of thawed and frozen Arctic soils considering frequency, temperature, texture and dry density

ABSTRACTA dielectric model was developed for thawed and frozen mineral soils, based on the refractive mixing dielectric formula and the dielectric measurement data for three soils collected in the Arctic tundra of the Yamal Peninsula. The refractive mixing dielectric model was used in conjunction with the Debye multi relaxation equations as a theoretical model to fit the measured complex relative permittivity spectra as a function of soil moisture and temperature. As a result, the dielectric spectroscopic parameters for the various components of water in the soil, such as the low- and high-frequency limits of the complex relative permittivity, the times of the corresponding relaxations, and the specific conductivity, were simultaneously determined for soils with different clay contents for all measured temperatures. As the theoretical temperature dependences of these parameters, the Clausius–Mossotti, Eyring, and linear equations for the conductivity were used. By using approximations of the measured data with these formulas, the parameters of the temperature-dependent model were derived, such as the coefficient of volume expansion, energy and entropy of activation, and coefficient of thermal conductivity. A set of the parameters discussed above in conjunction with the refractive mixing formula is a temperature- and mineralogically dependent multi-relaxation spectroscopic dielectric model, which enables estimation of the permittivity of moist soils as a function of dry soil density, moisture, frequency, temperature, and texture. The statistical error of the proposed dielectric model was estimated in terms of the normalized root-mean-square error (nRMSE), which was equal to 5% and 25% for the dielectric constant and dielectric loss factor, respectively.

Sphingorhabdus soli sp. nov., isolated from Arctic soil.

A Gram-stain-negative, strictly aerobic, rod-shaped and non-motile bacterial strain, designated D-2Q-5-6T, was isolated from a soil sample collected from the Arctic region. Strain D-2Q-5-6T was found to grow at 10-43 °C (optimum, 28 °C), at pH 6.0-9.0 (pH 7.0) and in 0-5 % (w/v) NaCl (0-1 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain D-2Q-5-6T fell into the genus Sphingorhabdus and shared less than 95.8 % identity with all type strains of recognized species of this genus. The major cellular fatty acids of strain D-2Q-5-6T were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c; 31.4 %), summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c; 26.8 %) and C14 : 0 2OH (11.7 %). The polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine and sphingoglycolipid. The predominant quinone was identified as Q10. The DNA G+C content of strain D-2Q-5-6T was 64.5 mol%. Based on the results of phylogenetic analysis and distinctive phenotypic characteristics, strain D-2Q-5-6T is concluded to represent a novel species of the genus Sphingorhabdus, for which the name Sphingorhabdus soli sp. nov. is proposed. The type strain of the species is D-2Q-5-6T (=MCCC 1A06070T=KCTC 52311T).

Mycobiont contribution to tundra plant acquisition of permafrost-derived nitrogen.

As Arctic soils warm, thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon losses from tundra ecosystems. Although mycorrhizal fungi could facilitate plant access to permafrost-derived N, their exploration capacity beyond host plant root systems into deep, cold active layer soils adjacent to the permafrost table is unknown. We characterized root-associated fungi (RAF) that colonized ericoid (ERM) and ectomycorrhizal (ECM) shrub roots and occurred below the maximum rooting depth in permafrost thaw-front soil in tussock and shrub tundra communities. We explored the relationships between root and thaw front fungal composition and plant uptake of a 15 N tracer applied at the permafrost boundary. We show that ERM and ECM shrubs associate with RAF at the thaw front providing evidence for potential mycelial connectivity between roots and the permafrost boundary. Among shrubs and tundra communities, RAF connectivity to the thaw boundary was ubiquitous. The occurrence of particular RAF in both roots and thaw front soil was positively correlated with 15 N recovered in shrub biomass Taxon-specific RAF associations could be a mechanism for the vertical redistribution of deep, permafrost-derived nutrients, which may alleviate N limitation and stimulate productivity in warming tundra.

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).

Anaerobic respiration pathways and response to increased substrate availability of Arctic wetland soils.

The availability of labile carbon (C) compounds in Arctic wetland soils is expected to increase due to thawing permafrost and increased fermentation as a result of decomposition of organic matter with warming. How microbial communities respond to this change will affect the balance of CO2 and CH4 emitted during anaerobic organic matter decomposition, and ultimately the net radiative forcing of greenhouse gas emissions from these soils. While soil water content limits aerobic respiration, the factors controlling methanogenesis and anaerobic respiration are poorly defined in suboxic Arctic soils. We conducted incubation experiments on two tundra soils from field sites on the Seward Peninsula, Alaska, with contrasting pH and geochemistry to determine the pathways of anaerobic microbial respiration and changes with increasing substrate availability upon warming. In incubation of soils from the circumneutral Teller site, the ratio of CO2 to CH4 dropped from 10 to <2 after 60 days, indicating rapid depletion of alternative terminal electron acceptors (TEAs). Addition of acetate stimulated production of CO2 and CH4 in a nearly 1 : 1 ratio, consistent with methanogenesis, and the composition of the microbial community shifted to favor clades capable of utilizing the added acetate such as the Fe(iii)-reducing Geobacter and the methanogenic archaea Methanosarcina. In contrast, both CO2 and CH4 production declined with acetate addition during incubation of soils from the more acidic Council site, and fermentative microorganisms increased in abundance despite the high availability of fermentation products. These results demonstrate that the degree to which increasing substrate availability stimulates greenhouse gas production in tundra wetlands will vary widely depending on soil pH and geochemistry.

Changes in ice‐wedge activity over 25 years of climate change near Salluit, Nunavik (northern Québec, Canada)

AbstractTo assess the direct impact of climate change on ice‐wedge (IW) degradation, 16 sites in the Narsajuaq river valley (Nunavik, Canada) that were extensively studied between 1989 and 1991 were revisited in 2016, 2017 and 2018. In total, 109 pits were dug to record soil characteristics and IW shapes and depths. Changes in surface conditions were also noted using side‐by‐side comparisons of recent (2017) and older (1989–1991) land and aerial photographs. During the past 25 years, the active layer reached depths that were 1.2–3.4 times deeper than in 1991, which led to the widespread degradation of IWs in the valley. Whereas 94% of the IWs unearthed in 1991 showed multiple recent growth structures, only 13% of the 55 IWs unearthed in 2017 still had some upgrowth stages left. IW tops are now consistently deeper than the main stages of the IWs measured in 1991. In August 2017, however, about half of the IWs had ice veins connecting them to the base of the active layer, an indication that the recent cooling spell (2010 to present) in the region was enough to reactivate frost cracking and IW growth. This paper highlights how sensitive the Arctic soil system can be to short‐term climate variations.

Arctic soil carbon turnover controlled by experimental snow addition, summer warming and shrub removal

Northern latitude tundra heaths have accumulated large amounts of organic carbon (C) in the soil. Changes in climatic conditions such as temperature and winter precipitation might affect the C balance and potentially change these tundra ecosystems from being C sinks to sources of CO2 emitted to the atmosphere. However, studies on C fluxes with single and combined winter snow and summer warming effects are scarce. This study investigates gross ecosystem production (GEP), ecosystem respiration (ER), net ecosystem production (NEP) and carbon isotopic composition of CO2 emitted from a dry heath in arctic Greenland one and two years following field manipulations of summer temperature, shrub abundance and winter snow depth. Our aims were to quantify climatic change effects on CO2 fluxes and the growing season carbon balance of the ecosystem and to investigate shifts in δ13C of emitted CO2 potentially due changes in emission from old soil C versus recently fixed carbon. Ecosystem CO2 fluxes and δ13C-CO2 were measured using closed chambers, and soil CO2 concentrations and δ13C were measured depth-specifically using gas probes.We found a significant increase of CO2 emissions in all treatments during both years. Growing season NEP increased by 38 and 73% with 1 m enhanced winter snow depth, by 113 and 144% with summer warming and by 61 and 320% with total shrub removal in 2013 and 2014, respectively. The snow effect can be explained by the delay in the onset of growth as indicated by early season reduced vegetation greenness. The effect of warming was a result of an increase of ER by 39 and 32%, and the effect of shrub removal was mainly due to a reduction in GEP by 34 and 48%, in 2013 and 2014, respectively. Furthermore, the δ13C of the carbon source of CO2 emitted from warmed plots increased significantly two years after the experiment was initiated. This might indicate increased decomposition of 13C enriched soil organic matter and hence increased mineralization of the old carbon stock in the soil under warmed conditions. The increase of NEP, the additive response of all treatments, and the indications of increased emission of carbon from old stocks due to warming (or warming-induced drying), demonstrate the risk of a relatively fast feedback to climate warming during the snow-free season.

Arctic Soil Governs Whether Climate Change Drives Global Losses or Gains in Soil Carbon

AbstractKey uncertainties in terrestrial carbon cycle projections revolve around the timing, direction, and magnitude of the carbon cycle feedback to climate change. This is especially true in carbon‐rich Arctic ecosystems, where permafrost soils contain roughly one third of the world's soil carbon stocks, which are likely vulnerable to loss. Using an ensemble of soil biogeochemical models that reflect recent changes in the conceptual understanding of factors responsible for soil carbon persistence, we quantify potential soil carbon responses under two representative climate change scenarios. Our results illustrate that models disagree on the sign and magnitude of global soil changes through 2100, with disagreements primarily driven by divergent responses of Arctic systems. These results largely reflect different assumptions about the nature of soil carbon persistence and vulnerabilities, underscoring the challenges associated with setting allowable greenhouse gas emission targets that will limit global warming to 1.5°C.