Arctic Soils Research Articles

The “Plastisphere” of Biodegradable Plastics Is Characterized by Specific Microbial Taxa of Alpine and Arctic Soils

Plastic pollution poses a threat to terrestrial ecosystems, even impacting soils from remote alpine and arctic areas. Biodegradable plastics are a promising solution to prevent long-term accumulation of plastic litter. However, little is known about the decomposition of biodegradable plastics in soils from alpine and polar ecosystems or the microorganisms involved in the process. Plastics in aquatic environments have previously been shown to form a microbial community on the surface of the plastic distinct from that in the surrounding water, constituting the so-called ‘plastisphere’. Comparable studies in terrestrial environments are scarce. Here, we aimed to characterize the plastisphere microbiome of three types of plastics differing in their biodegradability in soil using DNA metabarcoding. Polylactic acid (PLA), polybutylene adipate terephthalate (PBAT) and polyethylene (PE) were buried in two different soils, from the Swiss Alps and from Northern Greenland, at 15°C for eight weeks. While physico-chemical characteristics of the polymers only showed minor (PLA, PBAT) or no (PE) changes after incubation, a considerably lower α-diversity was observed on the plastic surfaces and prominent shifts occurred in the bacterial and fungal community structures between the plastisphere and the adjacent bulk soil not affected by the plastic. Effects on the plastisphere microbiome decreased with greater biodegradability of the plastics, from PLA to PE. Copiotrophic taxa within the phyla Proteobacteria and Actinobacteria benefitted the most from plastic input. Especially taxa with a known potential to degrade xenobiotics, including Burkholderiales, Caulobacterales, Pseudomonas, Rhodococcus and Streptomyces, thrived in the plastisphere of the Alpine and Arctic soils. In addition, Saccharimonadales (superphylum Patescibacteria) was identified as a key taxon associated with PLA. The association of Saccharibacteria with plastic has not been reported before, and pursuing this finding further may shed light on the lifestyle of this obscure candidate phylum. Plastic addition affected fungal taxa to a lesser extent since only few fungal genera such as Phlebia and Alternaria were increased on the plastisphere. Our findings suggest that the soil microbiome can be strongly influenced by plastic pollution in terrestrial cryoenvironments. Further research is required to fully understand microbial colonization on plastic surfaces and the biodegradation of plastic in soils.

Molecular-mass distribution of humic substances from Arctic soils according to size exclusion chromatography

Molecular-mass distribution of humic substances from Arctic soils according to size exclusion chromatography

Chryseobacterium antibioticum sp. nov. with antimicrobial activity against Gram-negative bacteria, isolated from Arctic soil.

A yellow-pigmented, non-motile, Gram-stain-negative, pleomorphic bacterium, designated RP-3-3T was obtained from soil sampled at the Arctic region in Cambridge Bay, NU, Canada. The strain is strictly aerobic, psychrotolerant, grow optimally at 15-20 °C and produces flexirubin type pigments. The strain is able to hydrolyse CM-cellulose, casein, starch and DNA. Strain RP-3-3T showed antimicrobial activity against Gram-negative pathogens. A phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain RP-3-3T formed a lineage within the family Weeksellaceae and clustered as members of the genus Chryseobacterium. The closest members were Chryseobacterium shigense DSM 17126T (98.7% sequence similarity), Chryseobacterium carnipullorum DSM 25581T (98.7%) and Chryseobacterium oncorhychi 701B-08T (98%). The genome is 4,910,468 bp long with 73 scaffolds and 4300 protein-coding genes. The anti-SMASH analysis of whole genome showed ten putative biosynthetic gene clusters responsible for various secondary metabolites. The sole respiratory quinone is MK-6. The major cellular fatty acids are iso-C15:0, iso-C17:1 ω9c, iso-C17:0 3-OH, summed feature 3 (iso-C15 :0 2-OH/C16 :1ω7c) and anteiso-C15:0. The major polar lipid is phosphatidylethanolamine. The DNA G + C content of the type strain is 36.9 mol%. In addition, the average nucleotide identity and in silico DNA-DNA hybridization relatedness values between strain RP-3-3T and phylogenetically closest members are below the threshold value for species delineation. Based on genomic, chemotaxonomic, phenotypic and phylogenetic analyses, strain RP-3-3T represents novel species in the genus Chryseobacterium, for which the name Chryseobacterium antibioticum sp. nov. is proposed. The type strain is RP-3-3T (=KACC 21620T = NBRC 114360T).

Complexation of lead and cadmium ions with humic acids from arctic peat soils

Humic acids (HAs) have many significant environmental and geochemical functions in soils, bottom sediments, and aquatic environments. Their interaction with toxic heavy metal ions affects their transport and bioavailability. This study suggests that binding of heavy metal ions to HAs could potentially help to develop strategies for recovering metal-contaminated soils and groundwater. This study is aimed at investigation of sorption properties of HA preparations from peat soils based on determining the kinetic and thermodynamic parameters of the sorption processes of Cd2+ and Pb2+ ions. Based on a model experiment, the binding ability of HAs of Hemic Folic Cryic Histosol to Cd2+ and Pb2+ ions was revealed. It is shown that during the initial stage (first 20 min for Cd2+ ions and 30 min for Pb2+ ions) the kinetics of the process of sorption of metal ions by suspended HA preparations is better described by pseudo-second order equation. This indicates the chemisorption mechanism and limiting contribution of chemical reaction. The kinetics sorption process within the Boyd – Adamson – Myers model is described with high precision for both ions during the whole experiment. This indicates the intra-diffusion limitation of the sorption process. The thermodynamic characteristics (the limiting sorption capacity, constant of sorption equilibrium, Gibbs free energy change, entropy change and enthalpy change of sorption) of the sorption process of selected heavy metal ions have been calculated. It was found that the limiting specific sorption of Pb2+ ions is almost an order of magnitude higher than that of Cd2+ ions and amounts to 0.16–0.29 mmol/dm3 and 0.0078–0.034 mmol/dm3, respectively. The sorption enthalpy variance of 48.4 kJ/mol for Cd2+ ions and 22.6 kJ/mol for Pb2+ ions indicate the endothermic nature of sorption on HA solid particles. It was shown that the limiting stage of sorption for Cd2+ and Pb2+ ions is ion diffusion to the sorbent, while chemisorption itself proceeds quite quickly. Values ΔS> −10 J/(mol ∙ K) indicate a dissociative sorption mechanism for both metals, i.e. non-sorbed ions in the solution are in a more ordered state than after sorption. The negative values of the Gibbs free energy change for Cd2+ and Pb2+ ions indicate that the interaction of ions with HA preparations from peat soils is a spontaneous process with a complex mechanism involving complexation and ion exchange processes.

Labile carbon limits late winter microbial activity near Arctic treeline

Soil microbial communities remain active during much of the Arctic winter, despite deeply frozen soils. Overwinter microbial activity affects the global carbon (C) budget, nutrient cycling, and vegetation composition. Microbial respiration is highly temperature sensitive in frozen soils, as liquid water and solute availability decrease rapidly with declining temperature. Climate warming and changes in snowpack are leading to warmer Arctic winter soils. Warmer winter soils are thought to yield greater microbial respiration of available C, greater overwinter CO2 efflux and greater nutrient availability to plants at thaw. Using field and laboratory observations and experiments, we demonstrate that persistently warm winter soils can lead to labile C starvation and reduced microbial respiration, despite the high C content of most Arctic soils. If winter soils continue to warm, microbial C limitation will reduce expected CO2 emissions and alter soil nutrient cycling, if not countered by greater labile C inputs.

Microfungi, algae and cyanobacteria in soils polluted with fluorine (Kola Peninsula, Russia)

The analysis of algal-mycological complexes in Albic Podzolic soils affected by emissions of the Kandalaksha Aluminum Smelter (KAS) was carried out. The number and biomass of microscopic fungi in the maximum fluorine-polluted zone (fluorine-content >1000 mg/kg) more than 2 times lower than in distanced areas and amounted to 17.3 thousants colony-forming units/g and 1.33 mg/g respectively. Altogether, 31 species of soil fungi were isolated. The species Penicillium trzebinskii and P. miczynskii dominated the zone of maximum pollution. P. glabrum, P. spinulosum, and Memnoniella echinata prevailed in the zones of moderate pollution and background. The part of opportunistic fungi in contaminated soil increased in comparison with the background soil. The reduction of dark-colored fungi biomass in contaminated soil was noted. In total, 56 species of eukaryotic algae and 7 species of cyanobacteria were found. Among green algae, the species from families Chlorophyceae and Trebouxiophyceae dominated in all plots. In the zones of maximum and strong contamination, 53 algae species were found including xanthophytes, which were absent in unpolluted areas. The number of viable cells in the litter of the maximum contaminated soils varied from 100 thousand to 1.5 million in 1 g of absolutely dry soil. The species composition of algae and cyanobacteria in these soils showed the characteristic features of the Arctic biological soil crusts.

Nutrient availability measurement techniques in arctic tundra soils: in situ ion exchange membranes compared to direct extraction

The use of ion exchange membranes (IEMs) as an alternative to direct chemical extractions for measuring soil nutrient availability has many theoretical advantages but was not well-investigated in the arctic. We compared the two methods in a low Arctic tundra ecosystem, and investigated the applicability of IEMs to determine experimental treatment effects on soil fertility and plant nutrient acquisition. We compared IEM incubation and soil sample water-extraction methods to assess the intra-seasonal availabilities of ammonium, nitrate, and phosphate in tundra soils from experimental fertilization treatments. We determined plant species’ foliar nutrient concentrations in those treatments to evaluate the effectiveness of the two methods in predicting plant nutrient acquisition. We also incubated IEMs in summer greenhouse warming and snowfence treatment soils and investigated the corresponding plant community biomass responses. NH4-N accumulations on IEMs across the fertilization treatments were closely correlated to NH4-N pools obtained by soil extraction. However, the IEM method was more sensitive and so was able to detect effects of low level fertilization that corresponded with increases in plant foliar nutrient concentrations. Furthermore, temporal pattern of IEM nutrient fluxes differed from the nutrient pools. The warming treatment enhanced phosphate but not ammonium fluxes, although plant community biomass increased. The snowfence treatment had no effects on either flux, and the overwinter fluxes of both nutrients were extremely low compared to the growing season. We conclude that the IEM method is a relatively sensitive, simple, and effective method for measuring nutrient availability in tundra soils.

Landscape-geochemical assessment of content of natural hydrocarbons in arctic and subarctic soils (Komi Republic, Russia)

The assessment of the natural background of the hydrocarbon (HC) concentrations in soils is an urgent task, the solution of which will allow us to objectively determine soil pollution and promptly introduce restrictions on industrial technologies of oil production, transportation, and refining. The purpose of this work is to assess the background content and to establish patterns of accumulation of HC in the Arctic and Subarctic soils taking into account the landscape-geochemical characteristics of the territories. The concentration of HC in soil samples was determined from the values of the fluorescence intensity of the hexane extract. It has been established that the accumulation and distribution of HC in the soil cover depend on several factors: the topography of the territory and the soil origin, the particle size distribution of the soil-forming rocks, and the content of soil organic matter. The maximum HC content was detected in the soils of accumulative landscapes, while it is minimum—in soils of eluvial territories. The profile differentiation of HC is more pronounced in soils formed on loams and less on sandy rocks. A database and a map of the distribution of natural HC in soils of the Komi Republic have been created.

Thawing permafrost: an overlooked source of seeds for Arctic cloud formation

As the Arctic warms at twice the global rate, radiative feedbacks from clouds will lead to compounding impacts on the surface energy budget that affect both regional and global weather, and climate. In a future warmer world, the Arctic is projected to become cloudier. However, the formation and evolution of Arctic clouds remain highly uncertain in part due to a limited understanding of current and future sources of ice nucleating particles (INPs). In particular, the sources and abundance of biologically-derived INPs are poorly characterized, yet they may be pivotal for cloud ice formation, especially at temperatures in which Arctic mixed-phase clouds (AMPCs) persist (i.e. >−15 °C). Here, we show for the first time that permafrost is a remarkably rich source of biologically-derived INPs, both heat labile (probably proteinaceous) and other organic INPs of biomolecular origin (41%–100% and 99%–100% of the total INPs, respectively). INP concentrations in 1000 to 30 000 year old permafrost were comparable to the most active of other Arctic and midlatitude soil sources (up to 1010 INPs per gram of soil). Thawing of permafrost—which promotes metabolic activity in microbes—and subsequent mobilization of those soils directly into the atmosphere or into lakes, rivers, and the ocean, suggests the intriguing possibility that increasing emissions of INPs from this hitherto overlooked reservoir could be widespread, and, in time, greatly impact Arctic cloud cloud glaciation and radiative properties. This discovery is timely given the rapidly-thawing permafrost in Alaska and across Earth’s high latitudes. Since permafrost covers 15% of Northern Hemisphere land, this novel and prevalent INP source may become central to predictions of aerosol-cloud-precipitation interactions in AMPCs.

Metabolism overrides photo‐oxidation in CO2 dynamics of Arctic permafrost streams

AbstractGlobal warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Abiotic photo‐oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 concentrations and the isotopic composition of dissolved inorganic C (δ13CDIC) at diel resolution in two Arctic streams, and coupled this with whole‐system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo‐oxidation is the dominant source of CO2. Instead, the observed decrease in CO2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ13CDIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ13CDIC values, suggesting that metabolic estimates are partly masked by O2 consumption from photo‐oxidation. Our results suggest that 6–12 mmol CO2‐C m−2 d−1 may be generated from photo‐oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo‐oxidation rates for these Arctic streams, and accounted for 33–80% of total CO2 evasion. Our results suggest that metabolic activity is the dominant process for CO2 production in Arctic streams. Thus, future aquatic CO2 emissions may depend on how biotic processes respond to the ongoing environmental change.

Methanotroph populations and CH4 oxidation potentials in high-Arctic peat are altered by herbivory induced vegetation change.

ABSTRACTMethane oxidizing bacteria (methanotrophs) within the genus Methylobacter constitute the biological filter for methane (CH4) in many Arctic soils. Multiple Methylobacter strains have been identified in these environments but we seldom know the ecological significance of the different strains. High-Arctic peatlands in Svalbard are heavily influenced by herbivory, leading to reduced vascular plant and root biomass. Here, we have measured potential CH4 oxidation rates and identified the active methantrophs in grazed peat and peat protected from grazing by fencing (exclosures) for 18 years. Grazed peat sustained a higher water table, higher CH4 concentrations and lower oxygen (O2) concentrations than exclosed peat. Correspondingly, the highest CH4 oxidation potentials were closer to the O2 rich surface in the grazed than in the protected peat. A comparison of 16S rRNA genes showed that the majority of methanotrophs in both sites belong to the genus Methylobacter. Further analyses of pmoA transcripts revealed that several Methylobacter OTUs were active in the peat but that different OTUs dominated the grazed peat than the exclosed peat. We conclude that grazing influences soil conditions, the active CH4 filter and that different Methylobacter populations are responsible for CH4 oxidation depending on the environmental conditions.

From fibrous plant residues to mineral-associated organic carbon – the fate of organic matter in Arctic permafrost soils

Abstract. Permafrost-affected soils of the Arctic account for 70 % or 727 Pg of the soil organic carbon (C) stored in the northern circumpolar permafrost region and therefore play a major role in the global C cycle. Most studies on the budgeting of C storage and the quality of soil organic matter (OM; SOM) in the northern circumpolar region focus on bulk soils. Thus, although there is a plethora of assumptions regarding differences in terms of C turnover or stability, little knowledge is available on the mechanisms stabilizing organic C in Arctic soils besides impaired decomposition due to low temperatures. To gain such knowledge, we investigated soils from Samoylov Island in the Lena River delta with respect to the composition and distribution of organic C among differently stabilized SOM fractions. The soils were fractionated according to density and particle size to obtain differently stabilized SOM fractions differing in chemical composition and thus bioavailability. To better understand the chemical alterations from plant-derived organic particles in these soils rich in fibrous plant residues to mineral-associated SOM, we analyzed the elemental, isotopic and chemical composition of particulate OM (POM) and clay-sized mineral-associated OM (MAOM). We demonstrate that the SOM fractions that contribute with about 17 kg C m−3 for more than 60 % of the C stock are highly bioavailable and that most of this labile C can be assumed to be prone to mineralization under warming conditions. Thus, the amount of relatively stable, small occluded POM and clay-sized MAOM that currently accounts with about 10 kg C m−3 for about 40 % of the C stock will most probably be crucial for the quantity of C protected from mineralization in these Arctic soils in a warmer future. Using δ15N as a proxy for nitrogen (N) balances indicated an important role of N inputs by biological N fixation, while gaseous N losses appeared less important. However, this could change, as with about 0.4 kg N m−3 one third of the N is present in bioavailable SOM fractions, which could lead to increases in mineral N cycling and associated N losses under global warming. Our results highlight the vulnerability of SOM in Arctic permafrost-affected soils under rising temperatures, potentially leading to unparalleled greenhouse gas emissions from these soils.

Methane oxidation potential of the arctic wetland soils of a taiga-tundra ecotone in northeastern Siberia

ABSTRACT Arctic wetlands are significant sources of atmospheric methane and the observed accelerated climate changes in the arctic could cause a change in methane dynamics. Methane oxidation would be the key process to control methane emission from wetlands. In this study, we determined the potential methane oxidation rate of the wetland soils of a taiga–tundra transition zone in northeastern Siberia. Peat soil samples were collected in summer from depressions covered with tussocks of sedges and Sphagnum spp. and from mounds vegetated with moss and larch trees. An aerobic bottle incubation experiment demonstrated that the soil samples collected from depressions in the moss- and sedge-dominated zones exhibited active methane oxidation with no time lag, while the mound soils showed no methane oxidation under the given conditions. The potential methane oxidation rates of the soils at 15°C ranged from 94 to 496 nmol h−1 g−1 dw. The immediate and active methane oxidation was observed over the depths studied (0–40 cm) including the water-saturated anoxic layers; the maximum methane oxidation rate was recorded in the layer above the water-saturated layer. The methane oxidation rate was temperature-dependent, but substantial methane oxidation was observed even at 0°C particularly for the moss soil samples. Soil samples collected from the frozen layer of Sphagnum peat also showed immediate methane consumption when incubated at 15°C. The present results suggest that the methane oxidizing bacteria in the wetland soils could survive under anoxic and frozen conditions keeping their potential activities and immediately utilize methane when the conditions become favorable. On the other hand, the inhibitor of methane oxidation (difluoromethane) did not affect the methane flux from the sedge and moss zones in situ, which suggested the minor role of plant-associated methane oxidation.

Biogenic Volatile Organic Compounds in Arctic Soil: A Field Study of Concentrations and Variability With Vegetation Cover

AbstractSoil biogenic volatile organic compounds (sBVOCs) contribute to ecosystem emissions and play an important role in the soil ecosystem. Most previous studies on sBVOCs have looked at emissions from excavated soil in the laboratory or in situ emissions from areas with bare soil, using chambers. So far, however, the actual BVOC concentrations in the soil have rarely been considered. Herein, we sought to explore the relationships between the vegetation cover in a low Arctic heath ecosystem in Western Greenland and the BVOC concentration in the soil below. In situ measurements were performed at 15‐cm depth in areas dominated by Cassiope tetragona, Empetrum nigrum, Salix glauca, and Betula nana and along a 36‐m‐long transect with mixed vegetation cover during the growing seasons of 2015–2017. sBVOC concentrations varied between the different vegetation covers, with higher concentrations below Cassiope and Betula compared to Empetrum. Furthermore, sBVOC concentrations differed along the transect, and this variation was also partly related to differences in the vegetation cover. Moreover, we demonstrate that installation of a soil probe, for sampling soil air, changes the composition and magnitude of sBVOCs up to 1 day after the installation.

Expansion of shrubs could result in local loss of soil bacterial richness in Western Greenland.

Climate warming in Greenland is facilitating the expansion of shrubs across wide areas of tundra. Given the close association between plants and soil microorganisms and the important role of soil bacteria in ecosystem functioning, it is of utmost importance to characterize microbial communities of arctic soil habitats and assess the influence of plant edaphic factors on their composition. We used 16S rRNA gene amplicons to explore the bacterial assemblages of three different soil habitats representative of a plant coverage gradient: bare ground, biological soil crusts dominated by mosses and lichens and vascular vegetation dominated by shrubs. We investigated how bacterial richness and community composition were affected by the vegetation coverage, and soil pH, moisture and carbon (C), nitrogen (N) and phosphorus (P) contents. Bacterial richness did not correlate with plant coverage complexity, while community structure varied between habitats. Edaphic variables affected both the taxonomic richness and community composition. The high number of Amplicon Sequence Variants (ASVs) indicators of bare ground plots suggests a risk of local bacterial diversity loss due to expansion of vascular vegetation.

Arctic Amplification of Global Warming Strengthened by Sunlight Oxidation of Permafrost Carbon to CO2

AbstractOnce thawed, up to 15% of the ∼1,000 Pg of organic carbon (C) in arctic permafrost soils may be oxidized to carbon dioxide (CO2) by 2,100, amplifying climate change. However, predictions of this amplification strength ignore the oxidation of permafrost C to CO2 in surface waters (photomineralization). We characterized the wavelength dependence of permafrost dissolved organic carbon (DOC) photomineralization and demonstrate that iron catalyzes photomineralization of old DOC (4,000–6,300 a BP) derived from soil lignin and tannin. Rates of CO2 production from photomineralization of permafrost DOC are twofold higher than for modern DOC. Given that model predictions of future net loss of ecosystem C from thawing permafrost do not include the loss of CO2 to the atmosphere from DOC photomineralization, current predictions of an average of 208 Pg C loss by 2,299 may be too low by ~14%.

The effects of warming and soil chemistry on bacterial community structure in Arctic tundra soils

Soil microbial communities in the Arctic play a critical role in regulating the global carbon (C) cycle. Vast amounts of C are stored in northern high latitude soils, and rising temperatures in the Arctic threaten to thaw permafrost, making relatively inaccessible C sources more available for mineralization by soil microbes. Few studies have characterized how microbial community structure responds to thawing permafrost in the context of varying soil chemistries associated with contrasting tundra landscapes. We subjected active layer and permafrost soils from upland and lowland tundra sites on the North Slope of Alaska to a soil-warming incubation experiment and compared soil bacterial community profiles (obtained by 16S rRNA amplicon sequencing) before and after incubation. The influence of soil composition (characterized by mid-infrared [MIR] spectroscopy) on bacterial community structure and class abundance was analyzed using redundancy and correlation analyses. We found increased abundances of Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes [Sphingobacteriia] post incubation, particularly in permafrost soils. The categorical descriptors site and soil layer had the most explanatory power in our predictive models of bacterial community structure, highlighting the close relationship between soil bacteria and the soil environment. Specific soil chemical attributes characterizing the soil environments that were found to be the best predictors included MIR spectral bands associated with inorganic C, silicates, amide II (CN stretch), and carboxylics (C–O stretch), and MIR peak ratios representing C substrate quality. Overall, these results further characterize soil bacterial community shifts that may occur as frozen environments with limited access to C sources, as is found in undisturbed permafrost, transition to warmer and more C-available environments, as is predicted in thawing permafrost due to climate change.

Concentrations and distribution of novel brominated flame retardants in the atmosphere and soil of Ny-Ålesund and London Island, Svalbard, Arctic

Novel brominated flame retardants (NBFRs) were investigated in Arctic air and soil samples collected from Ny-Ålesund and London Island, Svalbard, during Chinese scientific research expeditions to the Arctic during 2014–2015. The concentrations of Σ9NBFRs in the Arctic air and soil were 4.9–8.7 pg/m3 (average 6.8 pg/m3) and 101–201 pg/g dw (average 150 pg/g dw), respectively. The atmospheric concentration of hexabromobenzene (HBB) was significantly correlated with that of pentabromotoluene (PBT) and pentabromobenzene (PBBz), suggesting similar source and environmental fate in the Arctic air. No significant spatial difference was observed among the different sampling sites, both for air and soil samples, indicating that the effects of the scientific research stations on the occurrence of NBFRs in the Arctic were minor. The fugacities from soil to air of pentabromoethylbenzene (PBEB), 2,3-dibromopropyl 2,4,6-tribromophenyl ether (DPTE), and decabromodiphenylethane 1,2-bis (pentabromophenyl) ethane (DBDPE) were lower than the equilibrium value, indicating a nonequilibrium state of these compounds between air and soil, the dominant impact of deposition and the net transport from air to soil. The correlation analysis between the measured and predicted soil-atmosphere coefficients based on the absorption model showed that the impact of the soil organic matter on the distribution of NBFRs in the Arctic region was minor. To the best of our knowledge, this work is one of the limited reports on atmospheric NBFRs in the Arctic and the first study to investigate the occurrence and fate of NBFRs in the Arctic soil.

Winter warming in Alaska accelerates lignin decomposition contributed by Proteobacteria

BackgroundIn a warmer world, microbial decomposition of previously frozen organic carbon (C) is one of the most likely positive climate feedbacks of permafrost regions to the atmosphere. However, mechanistic understanding of microbial mediation on chemically recalcitrant C instability is limited; thus, it is crucial to identify and evaluate active decomposers of chemically recalcitrant C, which is essential for predicting C-cycle feedbacks and their relative strength of influence on climate change. Using stable isotope probing of the active layer of Arctic tundra soils after depleting soil labile C through a 975-day laboratory incubation, the identity of microbial decomposers of lignin and, their responses to warming were revealed.ResultsThe β-Proteobacteria genus Burkholderia accounted for 95.1% of total abundance of potential lignin decomposers. Consistently, Burkholderia isolated from our tundra soils could grow with lignin as the sole C source. A 2.2 °C increase of warming considerably increased total abundance and functional capacities of all potential lignin decomposers. In addition to Burkholderia, α-Proteobacteria capable of lignin decomposition (e.g. Bradyrhizobium and Methylobacterium genera) were stimulated by warming by 82-fold. Those community changes collectively doubled the priming effect, i.e., decomposition of existing C after fresh C input to soil. Consequently, warming aggravates soil C instability, as verified by microbially enabled climate-C modeling.ConclusionsOur findings are alarming, which demonstrate that accelerated C decomposition under warming conditions will make tundra soils a larger biospheric C source than anticipated.DcAwnKbrAmVskAnqeJFRkXVideo

Empirical Models for Predicting Water and Heat Flow Properties of Permafrost Soils

AbstractWarming and thawing in the Arctic are promoting biogeochemical processing and hydrologic transport in carbon‐rich permafrost and soils that transfer carbon to surface waters or the atmosphere. Hydrologic and biogeochemical impacts of thawing are challenging to predict with sparse information on arctic soil hydraulic and thermal properties. We developed empirical and statistical models of soil properties for three main strata in the shallow, seasonally thawed soils above permafrost in a study area of ~7,500 km2 in Alaska. The models show that soil vertical stratification and hydraulic properties are predictable based on vegetation cover and slope. We also show that the distinct hydraulic and thermal properties of each soil stratum can be predicted solely from bulk density. These findings fill the gap for a sparsely mapped region of the Arctic and enable regional interpolation of soil properties critical for determining future hydrologic responses and the fate of carbon in thawing permafrost.