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Wildfire frequency and expanse in the Arctic have increased in recent years and are projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in Arctic ecosystems. We investigated in situ effects of an experimental fire in 2017 on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) surface fluxes in the most abundant tundra ecosystem in West Greenland in ambient and warmer conditions. Measurements from the growing seasons 2017 to 2019 showed that burnt areas became significant net CO2 sources for the entire study period, driven by increased ecosystem respiration (ER) immediately after the fire and decreased gross ecosystem production (GEP). Warming by open‐top chambers significantly increased both ER and GEP in control, but not in burnt plots. In contrast to CO2, measurements suggest that the overall sink capacity of atmospheric CH4, as well as net N2O emissions, were not affected by fire in the short term, but only immediately after the fire. The minor effects on CH4 and N2O, which was surprising given the significantly higher nitrate availability observed in burnt plots. However, the minor effects are aligned with the lack of significant effects of fire on soil moisture and soil temperature. Net uptake and emissions of all three GHG from burnt soils were less temperature‐sensitive than in the undisturbed control plots. Overall, this study highlights that wildfires in a typical tundra ecosystem in Greenland may not lead to markedly increased net GHG emissions other than CO2. Additional investigations are needed to assess the consequences of more severe fires. [ABSTRACT FROM AUTHOR]

Future Arctic tundra primary productivity and vegetation community composition will partly be determined by nitrogen (N) availability in a warmer climate. N mineralization rates are predicted to increase in both winter and summer, but because N demand and –mobility varies across seasons, the fate of mineralized N remains uncertain. N mineralized in winter is released in a "pulse" upon snowmelt and soil thaw, with the potential for lateral redistribution in the landscape. In summer, the release is into an active rhizosphere with high local biological N demand. In this study, we investigated the ecosystem sensitivity to increased lateral N input and near-surface warming, respectively and in combination, with a numerical ecosystem model (CoupModel) parameterized to simulate ecosystem biogeochemistry for a tundra heath ecosystem in West Greenland. Both measurements and model results indicated that plants were poor utilizers of increased early-season lateral N input, indicating that higher winter N mineralization rates may have limited impact on plant growth and carbon (C) sequestration for a hillslope ecosystem. The model further suggested that, although deciduous shrubs were the plant type with overall most lateral N gain, evergreen shrubs appear to have a comparative advantage utilizing early-season N. In contrast, near-surface summer warming increased plant biomass and N uptake, moving N from soil to plant N pools, and offered an advantage to deciduous plants. Neither simulated high lateral N fluxes nor near-surface soil warming suggests that mesic tundra heaths will be important sources of N2O under warmer conditions. Our work highlights how winter and summer warming may play different roles in tundra ecosystem N and C budgets depending on plant community composition. [ABSTRACT FROM AUTHOR]

Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic. [ABSTRACT FROM AUTHOR]

Aims: Plant growth in the Arctic is often nutrient limited due to temperature constraints on decomposition and low atmospheric input of nitrogen (N). Local hotspots of nutrient enrichment found in up to 4000-year-old archaeological deposits can be used to explore the recycling and long-term retention of nutrients in arctic ecosystems. Methods: We investigated old Inuit and Norse deposits (known as middens) and adjacent tundra ecosystems along a wet-dry fjord gradient in western Greenland to explore the isotopic fingerprinting of plant and soil carbon and nitrogen (13C/12C and 15N/14N) derived from human presence. Results: At all locations we observed a significant isotopic fingerprint in soil and plant N related to human deposits. This demonstrates a century-long legacy of past human habitation on plant and soil characteristics and indicates a surprisingly high N retention in these ecosystems. This is consistent with the significantly higher plant biomass in areas with archaeological deposits. Conclusion: Vegetation composition and N in plants and soils displayed marked differences along the wet-dry fjord gradient. Furthermore, the profound nutrient enrichment and organic matter accumulation in archaeological deposits compared to surrounding tundra demonstrates a century-long legacy of past habitation on plant and soil characteristics as well as efficient N cycling with surprisingly limited N loss. [ABSTRACT FROM AUTHOR]

Arctic and boreal peatlands play a major role in the global carbon (C) cycle. They are particularly efficient at sequestering carbon because their high water content limits decomposition rates to levels below their net primary productivity. Their future in a climate-change context is quite uncertain in terms of carbon emissions and carbon sequestration. Nuuk fen is a well-instrumented Greenlandic fen with monitoring of soil physical variables and greenhouse gas fluxes (CH4 and CO2) and is of particular interest for testing and validating land-surface models. But knowledge of soil carbon stocks and profiles is missing. This is a crucial shortcoming for a complete evaluation of models, as soil carbon is one of the primary drivers of CH4 and CO2 soil emissions. To address this issue, we measured, for the first time, soil carbon and nitrogen density, profiles and stocks in the Nuuk peatland (64 ∘ 07 ′ 51 ′′ N, 51 ∘ 23 ′ 10 ′′ W), colocated with the greenhouse gas measurements. Measurements were made along two transects, 60 and 90 m long and with a horizontal resolution of 5 m and a vertical resolution of 5 to 10 cm, using a 4 cm diameter gouge auger. A total of 135 soil samples were analyzed. Soil carbon density varied between 6.2 and 160.2 kg C m -3 with a mean value of 50.2 kg C m -3. Mean soil nitrogen density was 2.37 kg N m -3. Mean soil carbon and nitrogen stocks are 36.3 kg C m -2 and 1.7 kg N m -2. These new data are in the range of those encountered in other arctic peatlands. This new dataset, one of very few in Greenland, can contribute to further development of joint modeling of greenhouse gas emissions and soil carbon and nitrogen in land-surface models. The dataset is open-access and available at 10.1594/PANGAEA.909899. [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO2 concentration and climate change may substantially alter soil carbon (C) dynamics, which in turn may impact future climate through feedback cycles. However, only very few field experiments worldwide have combined elevated CO2 (eCO2) with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO2, warming, and drought, in all combinations for 8 years. At the end of the study, soil C stocks were on average 0.927 kg C/m2 higher across all treatment combinations with eCO2 compared to ambient CO2 treatments (equal to an increase of 0.120 ± 0.043 kg C m−2 year−1), and showed no sign of slowed accumulation over time. However, if observed pretreatment differences in soil C are taken into account, the annual rate of increase caused by eCO2 may be as high as 0.177 ± 0.070 kg C m−2 year−1. Furthermore, the response to eCO2 was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO2 observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO2 concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long‐term measurements of changes in soil C in response to the three major climate change‐related global changes, eCO2, warming, and changes in precipitation patterns, are, therefore, urgently needed. [ABSTRACT FROM AUTHOR]

• Low vs. high fire intensity lead to opposite responses of an Arctic soil microbiome. • Low fire intensity did not reduce tested genes while it promoted genes involved in N mineralization and archaeal nitrification. • High fire intensity reduced genes involved in N fixation/mineralization, P solubilization and denitrification. • Fire intensity is crucial for predictions of permafrost nutrient-climate feedbacks. Arctic tundra fires have been increasing in extent, frequency and intensity and are likely impacting both soil nitrogen (N) and phosphorus (P) cycling and, thus, permafrost ecosystem functioning. However, little is known on the underlying microbial mechanisms, and different fire intensities were neglected so far. To better understand immediate influences of different fire intensities on the soil microbiome involved in nutrient cycling in permafrost-affected soil, we deployed experimental fires with low and high intensity on an Arctic tundra soil on Disko Island, Greenland. Soil sampling took place three days postfire and included an unburned control. Using quantitative real-time PCR, copy numbers of 16S and ITS as well as of 17 genes coding for functional microbial groups catalyzing major steps of N and P turnover were assessed. We show that fires change the abundance of microbial groups already after three days with fire intensity as key mediating factor. Specifically, low-intensity fire significantly enhanced the abundance of chiA mineralizers and ammonia-oxidizing archaea, while other groups were not affected. On the contrary, high-intensity fire decreased the abundance of chiA mineralizers and of microbes that fix dinitrogen, indicating a dampening effect on N cycling. Only high-intensity fires enhanced ammonium concentrations (by an order of magnitude). This can be explained by burned plant material and the absence of plant uptake, together with impaired further N processing. Fire with high intensity also decreased nirK -type denitrifiers. In contrast, after fire with low intensity there was a trend for a decreased nosZ : (nirK + nirS) ratio, indicating – together with increased nitrate concentrations – an enhanced potential for nitric oxide and nitrous oxide emissions. Concerning P transformation, only gcd was affected in the short term which is important for P solubilization. Changes in gene numbers consistently showed the same contrasting pattern of elevated abundance with low fire intensity and decreased abundance with high fire intensity. Differentiating fire intensities is therefore crucial for further, longer-term studies of fire-induced changes in N and P transformations and potential nutrient-climate feedbacks of permafrost-affected soils. [ABSTRACT FROM AUTHOR]

• We investigated effects of fire in combination with summer warming in arctic tundra. • Fire increased soil organic P concentrations at least four years after the burning. • Summer warming reduced post-fire CO 2 losses by promoting vegetation recovery. • Soil heating at temperatures ≤ 55 °C had no immediate effects on soil GHG fluxes. The frequency and extent of wildfires in the Arctic has been increasing due to climate change. However, there is a lack of understanding about long-term impacts of climate warming on post-fire carbon dioxide (CO 2) exchange in arctic tundra ecosystems. To investigate this, we conducted an experimental low-intensity fire in combination with summer warming (using open top chambers) in a dry heath tundra ecosystem in West Greenland. We report here on the impact four and five years after the fire. We also examined immediate effects of soil heating to three temperature levels (35, 55 and 80 °C), as a simulation of heat transfer during a typical tundra fire. Fire increased soil organic phosphorus concentrations up to at least four years after the burning. The burned areas remained a net CO 2 source five years after the fire, mainly due to the lower aboveground vegetation biomass and reduced gross ecosystem production (GEP). However, with four to five years of summer warming, the GEP, ecosystem respiration and soil respiration significantly increased, and burned areas turned into a net CO 2 sink. Ex-situ soil heating to the temperature of 55 °C, reaching the heat load comparable with in-situ burning, had minor effects on soil GHG fluxes. This suggests that soil GHG activities are not immediately affected by heat transfer and associated soil temperature increases during a typical low-intensity wildfire in arctic dry tundra. Overall, our results reveal that in a future warmer climate, vegetation is likely to recover more quickly from fires, resulting in a reduction in post-fire CO 2 losses. [ABSTRACT FROM AUTHOR]

In the Arctic tundra, snowmelt is followed by soil thaw allowing water and dissolved nutrients to move downslope. However, the fate of the released nitrogen (N) remains unclear, which includes the fraction of N that is lost to downslope transport or converted to N gasses. We have quantified the release of NO 3 − into the soil solution and the loss of gaseous N upon thaw and up to a month after first thaw in an Arctic hillslope in W Greenland. We further investigated which factors of the slope ecosystem that influence the NO 3 − concentrations and N 2 O fluxes throughout two snowmelt and growing seasons using a Structural Equation Model (SEM) linking physical, biological and biogeochemical characteristics across the slope. Snowmelt controls growing season onset, but varies in the landscape. To account for this, we normalized the spatiotemporal variation in snowmelt and soil thaw by measuring NO 3 − release and N 2 O loss in a controlled laboratory thaw experiment with topsoil cores from along the slope. We furthermore normalized seasonal progression of ecosystem variables in space based on the first day of soil thaw in the field. We tested the variable Day After Soil Thaw (DAST) as the temporal driver in our SEM, and found that season progression is the most important factor to describe patterns in NO 3 − concentrations and N 2 O fluxes. We conclude that DAST is a useful tool for analysing seasonal patterns in a spatially heterogeneous snowmelt landscape and between different snowmelt years. When normalizing based on first day of soil thaw, we saw that the decreasing NO 3 − content over the season did not control the increasing N 2 O emissions. Rather, nitrification replaced denitrification as the main N 2 O -source during the growing season, where soil temperatures increased and soil moisture decreased. The gaseous N loss from the slope during the first month of thaw was minor and amounted to 1% of the annual N deposition. A NO 3 − pulse released into solution after 24 h of thaw, when meltwater moves along the slope and connects upslope with downslope ecosystems, thus constituted a "hot moment" for interaction between landscape N pools, but the NO 3 − was immobilized by microorganisms or taken up by plants rather than denitrified and did thus not constitute a hot moment for N 2 O emissions. Thus, our results regarding what drives the fate of spring-thaw released N in the sloping Arctic landscape highlight the importance of snowmelt timing and the following number of Day After Soil Thaw as a normalizing factor for biogeochemical processes. This provides an analytical concept for reducing spatial and inter-annual variability to understand general seasonal patterns otherwise hidden. • Spatial variability in snowmelt can confound biogeochemical seasonal patterns. • We monitored an Arctic slope during two very different snowmelt and soil thaw years. • We introduce the time variable Day After Soil Thaw in a Structural Equation Model. • Normalizing to variation in growing season onset unveiled biogeochemical patterns. • N 2 O emissions increased with season progression while NO 3 − availability decreased. [ABSTRACT FROM AUTHOR]

In recent years, wildfire frequency and severity has increased in the Arctic tundra regions due to climate change. Pyrogenic organic matter (PyOM) is a product of incomplete combustion of biomass containing nutrients such as nitrogen (N), and is expected to affect ecosystem N cycling during a post-fire recovery period. We investigated effects of fire on soil biogeochemical cycles with a focus on pyrogenic N turnover over two subsequent growing seasons, combined with and without summer warming, in an Arctic heath tundra, West Greenland. The summer warming was achieved by deployment of open top chambers (OTCs). We simulated an in situ tundra fire by removing vegetation and litter, and scorching/heating soil surface followed by the addition of 15N-labelled PyOM (derived from aboveground biomass and litter) to the soil surface in plots with and without summer warming. A darker surface after the simulated fire resulted in an increase of 1.3 °C in soil temperature at 5-cm depth over the growing seasons. The fire also caused a nine-fold increase in soil NH 4 +-N and three-fold increase in soil NO 3 −-N concentrations at 7-cm depth after two years. Tracing the fate of 15N-labelled PyOM, 21 days after its application, showed low 15N recovery in microbial biomass (0.4%) and total dissolved N (TDN) pools (0.01%). Microbial and root 15N recovery increased two-fold and 15-fold after one year, respectively, and TDN 15N recovery increased two-fold after two years, suggesting that relatively recalcitrant N of PyOM can be partly transformed into plant-available forms over time. Root and TDN 15N recovery was also significantly higher after two years of summer warming than under ambient temperature conditions, suggesting that summer warming can enhance availability of PyOM-N for recovering plants after the fire. Hence, we conclude that fire-induced PyOM can act as an N source for plant recovery in this Arctic tundra ecosystem for years after the fire, and this N source will become increasingly important in a future warmer climate. • Pyrogenic organic matter (PyOM) turnover after fire in an Arctic dry tundra. • There was a large loss of 15N-PyOM (30%) after 21 days. • The PyOM-N provided a N source to soil microbes and plants. • Summer warming enhanced availability of PyOM-N for plant re-growth. [ABSTRACT FROM AUTHOR]

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N 2 O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N 2 O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N 2 O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N 2 O averaged 1.7 μg N 2 O–N m−2 h−1 (range −3.6 to 10.5 μg N 2 O–N m−2 h−1), and generally increased from ambient (1 m) to moderate (2–3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N 2 O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N 2 O and nitrate (NO 3 −) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N 2 O fluxes were observed in the second half of August associated with high NO 3 − concentrations. The effect of growing season experimental warming on N 2 O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N 2 O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N 2 O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased winter precipitation leads to a deeper snow cover and a later snowmelt, total emissions of N 2 O from low Arctic heath ecosystems may be enhanced in the future and, dependent on dissolved N availability, summer warming may stimulate or reduce total emissions. [Display omitted] • We studied effects of warming on tundra N 2 O emissions along a snowmelt gradient. • The N 2 O emissions peaked with late snowmelt, likely due to high dissolved soil N. • Areas with highest snow depth (4 m) exhibited low N 2 O emissions (low temperature). • Experimental warming enhanced N 2 O emissions, where soil N was high (late snowmelt). • We conclude that low Arctic heath is a source to N 2 O regulated by dissolved soil N. [ABSTRACT FROM AUTHOR]

Arctic extreme winter warming events (WW events) have increased in frequency with climate change. WW events have been linked to damaged tundra vegetation ("Arctic browning"), but the mechanisms that link episodic winter thaw to plant damage in summer are not fully understood. We suggest that one mechanism is microbial N immobilization during the WW event, which leads to a smaller release of winter-mineralized N in spring and therefore more N limitation for vegetation in summer. We tested this hypothesis in a Western Greenlandic Low arctic tundra, where we experimentally simulated a 6 day field-scale extreme WW event and 1) used stable isotopes to trace the movement of N as a consequence of the WW event, 2) measured the effect of a WW event on spring N release in top soils in the laboratory, and 3) measured the carry-over effect on summer aboveground vegetation C/N ratio in tundra subject to a WW event. Our results show that soil mineral N released by a WW event followed by soil thaw is taken up by microbes and stored in the soil, whereas vascular plants acquired almost none, and significant amounts were lost to leaching and gaseous emissions. As soils thawed in spring, we saw weak but not significant evidence (P = 0.067) for a larger N release over the first month of spring thaw in Control soils compared to WW event soils, although not significantly. A weak signal (P = 0.07) linked WW event treatment to higher summer C/N ratios in evergreen shrubs, whereas deciduous shrubs were not affected. We conclude that our results did not show significant evidence for WW events causing Arctic browning via N immobilization and summer N limitation, but that we had indications (P < 0.1) which merits further testing of the theory in various tundra types and with repeated WW events. Evergreen shrubs could be especially sensitive to winter N immobilization, with implications for future vegetation community composition and tundra C storage. • It was tested whether N limitation due to winter warming (WW) causes N limitation in plants. • N uptake/release and plant N status were measured in a field-scale simulated WW event. • Soils and microbes immobilized WW-released N. • Spring N release tended to be smaller in soils subject to previous WW event. • Evergreen shrubs were more N limited if subjected to WW event previous winter. [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO2 concentration (eCO2) and climate change may significantly alter soil carbon (C) dynamics and thus feedback to future climate. However, only very few field experiments world-wide have combined eCO2 with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of carbon cycling in ecosystems. We exposed a temperate heath/grassland to eCO2, warming, and drought, in all combinations for 8 years. Soil C under ambient CO2 remained constant over time, whereas soil C stocks increased by 0.167 kg C m-2 yr-1 on average across all treatment combinations with eCO2 and showed no sign of slowed accumulation over time. Further, the response to eCO2 was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO2 observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO2 concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long-term measurements of changes in soil C in response to the three major climate change-related global changes, eCO2, warming, and changes in precipitation patterns, are therefore urgently needed. [ABSTRACT FROM AUTHOR]

Climate change may alter nutrient cycling in Arctic soils and plants. Deeper snow during winter, as well as summer warming, could increase soil temperatures and thereby the availability of otherwise limiting nutrients such as nitrogen (N). We used fences to manipulate snow depths in Svalbard for 9 consecutive years, resulting in three snow regimes: 1) Ambient with a maximum snow depth of 35 cm, 2) Medium with a maximum of 100 cm and 3) Deep with a maximum of 150 cm. We increased temperatures during one growing season using Open Top Chambers (OTCs), and sampled soil and vascular plant leaves throughout summer 2015. Labile soil N, especially inorganic N, during the growing season was significantly greater in Deep than Ambient suggesting N supply in excess of plant and microbial demand. However, we found no effect of Medium snow depth or short-term summer temperature increase on soil N, presumably due to minor impacts on soil temperature and moisture. The temporal patterns of labile soil N were similar in all snow regimes with high concentrations of organic N immediately after snowmelt, thereafter dropping towards peak growing season. Concentrations of all N forms increased at the end of summer. Vascular plants had high N at the start of growing season, decreasing as summer progressed, and leaf N concentrations were highest in Deep , corresponding to the higher soil N availability. Short-term summer warming was associated with lower leaf N concentrations, presumably due to growth dilution. Deeper snow enhanced labile soil organic and inorganic N pools and plant N uptake. Leaf 15N natural abundance levels (δ15N) in Deep indicated a higher degree of utilization of inorganic than organic N, which was especially pronounced in mycorrhizal plants. • Enhanced snow regimes cause high amounts of labile soil N during growing season. • Common tundra plants acquire more N in enhanced than in ambient snow regimes. • Common tundra plants acquire more inorganic N in enhanced snow regimes. [ABSTRACT FROM AUTHOR]

Impacts of increased winter snowfall and warmer summer air temperatures on nitrous oxide (N 2 O) dynamics in arctic tundra are uncertain. Here we evaluate surface N 2 O dynamics in both wet and dry tundra in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The potential denitrification activity (PDA) and potential net N 2 O production (N 2 O net) were measured to assess denitrification and N 2 O consumption potential. The surface N 2 O fluxes averaged 0.49 ± 0.42 and 2.6 ± 0.84 μg N 2 O–N m−2 h−1, and total emissions were 212 ± 151 and 114 ± 63 g N 2 O–N scaled to the entire study area of 0.15 km2, at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N 2 O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH 4 +-N or NO 3 −-N), but no main effect of deepened snow on N 2 O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N 2 O net at the dry and wet tundra, respectively, suggesting that N 2 O might be reduced and emitted as dinitrogen (N 2). Overall, this study reveals modest but evident surface N 2 O fluxes from tundra ecosystems in Western Greenland, and suggests that projected increases in winter precipitation and summer air temperatures may increase N 2 O emissions, particularly at the dry tundra dominating in this region. • We studied climate change effects on N 2 O fluxes in dry and wet tundra West Greenland. • Generally, N 2 O fluxes were relatively modest in both types of vegetation. • Summer warming combined with deepened snow enhanced N 2 O emissions in dry tundra. • Climate change did not affect N 2 O fluxes in wet tundra. [ABSTRACT FROM AUTHOR]

Many Arctic regions currently experience an increase in winter snowfall as a result of climate change. Deepened snow can enhance thermal insulation of the underlying soil during winter, resulting in warmer soil temperatures that promote soil microbial nitrogen (N)-cycle processes and the availability of N and other nutrients. We conducted an ex situ study comparing the effects of deepened snow (using snow fences that have been installed for 3–13 years) on microbial N-cycle processes in late summer (late growing season) and winter (late snow-covered season) among five tundra sites in three different geographic locations across the Arctic (Greenland (dry and wet tundra), Canada (mesic tundra), and Svalbard, Norway (heath and meadow tundra)). Soil gross N cycling rates (mineralization, nitrification, immobilization of ammonium (NH 4 +) and nitrate (NO 3 −), and denitrification) were determined using a15N pool dilution. Potential denitrification activity (PDA) and nitrous oxide reductase activity (N2OR) were measured to assess denitrifying enzyme activities. The deepened snow treatment across all sites had a significant effect of the potential soil capacity of accelerating N cycling rates in late winter, including quadrupled gross nitrification, tripled NO 3 −-N immobilization, and doubled denitrification as well as significantly enhanced late summer gross N mineralization, denitrification (two-fold) and NH 4 +-N availability. The increase in gross N mineralization and nitrification rates were primarily driven by the availability of dissolved organic carbon (DOC) and nitrogen (DON) across sites. The largest increases in winter DOC and DON concentrations due to deepened snow were observed at the two wetter sites (wet and mesic tundra), and N cycling rates were also more strongly affected by deepened snow at these two sites than at the three other drier sites. Together, these results suggest that the potential effects of deepened winter snow in stimulating microbial N-cycling activities will be most pronounced in relatively moist tundra ecosystems. Hence, this study provides support to prior observations that growing season biogeochemical cycles in the Arctic are sensitive to snow depth with altered nutrient availability for microorganisms and vegetation. It can be speculated that on the one hand growing season N availability will increase and promote plant growth, but on the other hand foster increased water- and gaseous (e.g. N 2 and N 2 O) N-losses with implications for overall nutrient status. • Deepened snow enhanced winter nitrification, NO 3 −-N immobilization, denitrification. • Deepened snow enhanced summer gross mineralization and denitrification. • The increases in N cycling rates were driven by the availability of DOC and DON. • The effects of deepened snow were most pronounced in wet tundra ecosystems. [ABSTRACT FROM AUTHOR]

Corrigendum to Mörsdorf et al. (2019) "Deepened winter snow significantly influences the availability and forms of nitrogen taken up by plants in High Arctic tundra" [Soil Biology & Biochemistry 135 222-234] 1 Daily averages of soil temperatures across all plots within respective treatments, in a depth of approx. one cm below soil surface. "T" represents plots within snow regimes that were temperature enhanced during summer, using OTCs. [Extracted from the article]