In this interdisciplinary session, focused on Arctic and boreal environments, we gather the latest developments in understanding the atmosphere-snow-plant-soil-microbe continuum. Our selected contributions explore how changes in the snowpack and increasing temperatures affect plants and soil organisms with a focus on resulting effects on biogeochemical cycling. This is approached across spatial scales, from earth system models to plot-level measurements, from field experiments to in vitro incubations, and even down to cells and genomes. Traditional plant and soil ecology methods as well as innovative stable isotope approaches provide insights into the mechanisms and seasonality of plant and microbial activity, priming effects, carbon exchange and nutrient cycling. Molecular methods, including environmental DNA, propose to document distribution and seasonal patterns of bacteria, micro-eukaryotes or soil fauna, and envision the modalities and impacts of their future changes. Bringing together cross-season and cross-taxa perspectives, this session will engage interdisciplinary discussions to jointly explore unknowns of Arctic terrestrial ecosystem functioning.
Orals: Thu, 1 May | Room 2.23
Cold season processes and emissions can be critical for determining annual budgets of CO2 and methane (CH4) in Arctic and other high-latitude ecosystems but there are relatively few measurements of winter fluxes and corresponding soil processes. In this talk, we will present results from investigating seasonality in greenhouse gas fluxes and processes controlling them, with a special emphasis on CH4 emissions from a boreal peatland. We measured CO2, CH4, and N2O fluxes for more than a year from an upland forest, dry bog, and wet bog at a site in boreal Finland using automated and manual chambers. Net CO2 uptake and CH4 emissions were highest in summer while N2O fluxes were nearly always below detection. Plant transport and oxidation of CH4 played an important role in CH4 fluxes during the summer as well as into the fall. CH4 emissions were enhanced throughout the fall due to plant transport and showed little seasonality in the fall in drier bog microtopographies. Net CO2 and CH4 emissions from the wet bog continued into December until snowpack formation, which led to an icy layer at the top of the peat profile. In the spring as snow melted and soils thawed, we saw an emissions pulse of CH4. Additional measurements showed the highest concentrations of CH4 in the peat porewater in the spring, indicating the accumulation of microbially-produced CH4 in the unfrozen peat under the snowpack during the winter. Furthermore, potential decomposition in Sphagnum peat showed little temperature sensitivity in laboratory experiments, indicating microbial adaptation to cold temperatures not seen in the dry bog or upland forest soils. Sustained biological activity in peat can continue at low temperatures over winter and lead to substantial enhancements in CH4 and CO2 emissions, although the timing of emissions is controlled by interactions in physical environment: snow melt, soil thawing, and plant-mediated transport.
How to cite: Treat, C. C., Jentzsch, K., van Delden, L., Hashemi, J., and Baysinger, M.: CO2 and CH4 fluxes and processes in a boreal bog and surroundings: a chilling tale of cold-season greenhouse gas emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3746, https://doi.org/10.5194/egusphere-egu25-3746, 2025.
Snow cover exerts contrasting influences above- and belowground, with shallower snow exposing shoots faster to warmer air temperatures in spring while causing colder soils and deeper soil frost. In contrast, increased snow depth insulates soils, keeping them warmer, but isolates shoots from warm air. Given that temperature is a key driver of phenological progression both above and below, snow cover changes may produce diverging effects on above- and belowground phenology, impacting spring carbon dynamics.
Over two years, we tracked snowmelt and spring green-up in a snow manipulation experiment (i.e., snow reduction, snow addition, control) at the EcoClimate site in a northern boreal rich fen (66°22' N). Our findings revealed that snow reduction advanced snow-free conditions for shoots but caused colder soils and delayed peat soil thawing. Snow reduction accelerated shoot phenology, but net carbon exchange remained similar to the control. In contrast, snow addition did not affect shoot phenology but reduced ecosystem respiration. Root growth was absent across all treatments during the first seven weeks of observation up to mid-summer, but follow-up measurements showed an increase in root density one month later.
These findings demonstrate that substantial shoot growth can occur independently of root growth. While snow reduction and addition did not produce divergent phenological patterns between aboveground and belowground processes—due to the delayed onset of root growth—changes in snow cover influenced carbon dynamics in complex ways. This study highlights the intricate interplay between winter snow cover, spring phenology, and CO2 exchange in high-latitude ecosystems.
How to cite: Cunow, J., Olofsson, J., Väisänen, M., and Blume-Werry, G.: Snow depth shapes aboveground but not belowground phenology during snowmelt, influencing carbon exchange in a northern boreal peatland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2050, https://doi.org/10.5194/egusphere-egu25-2050, 2025.
Sub-arctic tundra ecosystems experience strong seasonality, which could potentially influence the belowground processes, including the soil carbon cycling. Priming effect is a significant component in carbon cycling and describes the change of soil carbon mineralization after fresh carbon input. In this study, we investigated the effect of seasonality on the potential priming and the driving factors of the effect. We collected soils (0-10cm) from two tundra heath ecosystems with different precipitation regimes (Abisko and Vassijaure). We sampled soils every four weeks throughout a year and conducted 60-day incubation experiments at 3°C. To simulate the root exudate input effect, a 13C labelled artificial cocktail was added to assess the potential priming. Cumulative priming was positive throughout the whole year with fluctuations across sampling periods, accounting for significant portions of total respiration. While no significant seasonal variation on priming was observed, we found a significant snow state effect (snow-covered state vs snow-free state) on priming at both sites, with a trend of increasing priming potential during snow-covered periods. Surprisingly, the relationships between the driving factors – soil N availability (mineral N [NH4+ and NO3-], total dissolved N [DON]), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) – and priming remained consistent across snow states. Structural Equation Modeling (SEM) revealed that soil temperature and snow state influenced soil N availability (mineral N and dissolved organic N [DON]), DOC, and abundance of microbial communities (Bacteria and Archaea). DOC and MBC, along with bacterial abundance, positively influenced cumulative cocktail mineralization. Subsequently, cumulative cocktail mineralization strongly enhanced cumulative priming, whereas mineral nitrogen (N) availability had a suppressive effect. These results underscore the critical role of snow state in shaping potential priming, revealing consistent underlying drivers.
How to cite: Feng, C., Andersen, E. A. S., Turner, S., Merges, D., Klemmensen, K., Hallin, S., Olofsson, J., and Dorrepaal, E.: Distinct Potential Priming under Snow-Covered and Snow-Free Conditions in Subarctic Tundra, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8722, https://doi.org/10.5194/egusphere-egu25-8722, 2025.
Climate change has a strong impact on the duration and thickness of snow cover across the Arctic-Boreal region – possibly with negative consequences for both vegetation productivity and permafrost carbon loss. For example, a loss of snow cover combined with strong frost can lead to frost drought, damaging vegetation through desiccation. In other cases, increases in atmospheric moisture content can cause more mid-winter snowfall. Thicker snow cover in permafrost areas deepens the active layer, possibly amplifying the loss of soil carbon. However, the potential for shifts in snow cover to damage vegetation and to enhance permafrost carbon loss remains poorly quantified.
We used the dynamic global vegetation model LPJ-GUESS to show that mid-winter snow depths will increase by the end of the century in the coldest, northernmost regions of the permafrost region. This insulates the soil, raising soil temperatures, increasing heterotrophic respiration and reducing relative carbon residence times. In addition, we reveal the mechanisms underlying plant damage from frost droughts with the demographic vegetation model CLM-FATES, by showing how this affects cold hardening and plant hydraulics. These results suggest that the changing winter climate may be an important driver of carbon loss across the Arctic-Boreal region.
How to cite: Parmentier, F.-J. W., Pongracz, A., Lambert, M., Fisher, R. A., Gustafson, A., Miller, P. A., Rabin, S. S., Vollsnes, A., and Wårlind, D.: Contrasting shifts in snow depth as a driver of vegetation damage and soil carbon loss across the Arctic-Boreal region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16730, https://doi.org/10.5194/egusphere-egu25-16730, 2025.
The Arctic winter is disproportionately vulnerable to climate warming and approximately 1700 Gt of carbon stored in high latitude permafrost ecosystems is at risk of degradation in the future due to enhanced microbial activity. Few studies have been directed at high-latitude cold season land-atmosphere processes and it is suggested that the contribution of winter season greenhouse gas (GHG) fluxes to the annual carbon budget may have been underestimated. Snow, acting as a thermal blanket, influences Arctic soil temperatures during winter and parameters such as snow effective thermal conductivity (Keff) are not well constrained in land surface models which impacts our ability to accurately simulate wintertime soil carbon emissions. A point-model version of the Community Land Model (CLM5.0) forced by an ensemble of NA-CORDEX (North American Coordinated Regional Downscaling Experiment) future climate realisations (RCP 4.5 and 8.5) indicates that median winter CO2 emissions will have more than tripled by the end of the century (2066-2096) under RCP 8.5 and using a Keff parameterisation which is more representative of Arctic snowpack. Implementing this Keff parameterisation increases simulated winter CO2 in the latter half of the century (2066-2096) by 130% and CH4 flux by 50% under RCP 8.5 compared to the widely used default Keff parameterisation. The influence of snow Keff parameterisation within CLM5.0 on future simulated CO2 and CH4 is at least as significant, if not more so, than climate variability from a range of NA-CORDEX projections to 2100. Furthermore, CLM5.0 simulations show that enhanced future air and soil temperatures increases the duration of the early winter (Sept-Oct) zero-curtain, a crucial period of soil carbon emissions, by up to a month and recent increases in both zero-curtain and winter CO2 emissions appear set to continue to 2100. Modelled winter soil temperatures and carbon emissions demonstrate the importance of climate mitigation in preventing a significant increase in winter carbon emissions from the Arctic in the future.
How to cite: Rutherford, J., Rutter, N., Wake, L., and Cannon, A.: Snow thermal conductivity controls future winter carbon emissions in shrub-tundra, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4188, https://doi.org/10.5194/egusphere-egu25-4188, 2025.
The Arctic winter, which lasts for more than half the year, is not a simple, dormant phase as traditionally perceived. Instead, it involves active microbial processes under the snow cover, driven by soil temperature and moisture dynamics. These processes highlight the ongoing microbial activity and its potential interactions with the environment, challenging the notion of winter as a period of ecological dormancy. Variation in temperature, light, and snowfall throughout the winter can influence these processes, and therefore it is essential to study how climate-induced changes affect the synchronization, or phenological matches, between plant and microbial activities. Disruptions in this synchrony could lead to
In this study, we focus on bacterial and fungal communities, and their diversity and functional dynamics during winter and summer in heath and meadow vegetation across a climatic gradient ranging from the oceanic climate of western Norway to the continental climate near the Swedish-Finnish border. By integrating microbial community data, based on 16S rRNA gene, ITS amplicon sequencing, and metatranscriptomics (total RNA sequencing), with environmental and plant activity measurements, this study seeks to unravel the interactions between microbes and their environment, and particularly how they adapt to and function during the cold season. This research will provide critical insights into how winter conditions shape microbial community structure and function, ultimately enhancing our ability to predict the impacts of climate change across different Arctic ecosystems.
How to cite: Rodríguez, J., Pickering Pedersen, E., Feng, C., Gullvåg, R., Leblans, N., Dorrepaal, E., Olofsson, J., Clemmensen, K., and Hallin, S.: Seasonal Dynamics of Microbial Communities in Tundra Ecosystems Across a Climatic Gradient, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19895, https://doi.org/10.5194/egusphere-egu25-19895, 2025.
Terrestrial ecosystems provide key ecosystem services, yet their stability is increasingly threatened by global warming. There is, however, little consensus on how ecosystem functioning will respond to projected warming scenarios or when thresholds and tipping points may be crossed. This uncertainty arises largely from our limited understanding of the underlying non-linear responses of plants and soil organisms to temperature changes. Since plants and soil organisms often respond differently to warming, it can disrupt or decouple interactions among coexisting and co-evolved species, potentially leading to unforeseen consequences for key ecosystem functions, such as carbon and nutrient cycling.
Our ERC-THRESHOLD project aims to unravel these dynamics by investigating how non-linear temperature responses manifest across levels of ecological organization, including soil micro-organisms and soil fauna. We use forest-tundra and forest-alpine ecotones in seven countries across five continents to assess how plants, soil organisms, and ecosystem carbon cycling respond to increasing temperatures and how these responses may cross critical thresholds.
Preliminary findings show two key patterns. First, the slope of temperature profiles differs between aboveground and belowground measurements, with a steeper decline aboveground. This means that the difference between aboveground and belowground temperature declines with elevation. This has important implications for studying the effects of warming on soil food webs. Second, the shape of carbon flux responses along temperature gradients varies widely across transects and countries, indicating strong regional context dependence. Ongoing analyses of soil microorganisms and soil fauna aim to further elucidate these patterns
We also conduct growth chamber experiments to estimate how warming influences ecosystem carbon fluxes through the reorganization of plant and soil communities. In one experiment, subarctic heath vegetation monoliths were incubated at five warming levels, ranging from ambient to +9°C. While nematode density and community composition at the feeding group level remained relatively stable across warming treatments, individual nematode families exhibited diverse linear and non-linear responses. Soil micro-arthropods, including mites and springtails, showed generally weak responses to (short-term) warming, with patterns influenced by the dominant plant species. In another experiment, using the same temperature treatments, we are examining the warming responses of constructed tundra meadow communities and associated biogeochemical processes, both in absence and presence of soil microfauna. This experiment also tests the responses and effects of ‘encroaching’ ectomycorrhizal tree seedlings, specifically Betula pubescens subsp. czerepanovii.
Our ongoing work focuses on identifying the shapes of temperature "response functions" for plants, soil organisms, their communities, and the ecosystem processes they drive. By distinguishing linear from non-linear responses, we aim to better understand the mechanisms underlying ecosystem resilience and susceptibility to warming. Defining these response functions represents a critical frontier in global change research, offering insights into how terrestrial ecosystems may transition under future climate scenarios.
How to cite: Kardol, P., Kuťáková, E., Tanigawa, K., Lemoine, M., Setia Pradana, F., Li, B., Oberholzer, B., and Mallen Cooper, M.: Warming in the subarctic: Impacts on soil food webs and carbon cycling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4288, https://doi.org/10.5194/egusphere-egu25-4288, 2025.
Climate change affects herbivore populations and their migration patterns and feeding grounds in High-Arctic tundra ecosystems. Knowledge about the ecosystem-scaled impacts of environmental changes in the High-Arctic, including changes in herbivore grazing pressure, requires long-term perspectives and the integration of above- and belowground components.
Here we investigated the effects of grazing geese and reindeer on high-Arctic tundra, by studying the effects of short- (4 years) and long-term (14 y) exclusion of herbivores in situ. Within the Thiisbukta peatland, next to Ny-Ålesund (78.93°N, 11.92°E), Svalbard, 5 replicated high-Arctic wet tundra sampling sectors have been established. Each, at the time of sampling, included 4- and 14-year exclosure plots (Ex-4 and Ex-14), as well as control plots (Hr), where herbivory was not prevented.
Preventing herbivory altered a moss-dominated vegetation (Hr) to a mix of mosses and vascular plants (Ex-4) and a vascular-plant-dominated vegetation (Ex-14). These aboveground changes were reflected belowground and included a significant increase in root biomass and significantly higher contents of lignin derivates in the soil organic matter after the long-term exclusion of herbivores. Additionally, concentrations of inorganic phosphorous and monosaccharides (namely glucose and N-acetyl-glucosamine) were also increased after the long-term exclusion, while soil pH and moisture decreased. To study the effects of these alterations on soil organisms and their complex communities we employed metatranscriptomics, allowing us the simultaneous investigation of soil organisms across domains and kingdoms, ranging from Bacteria, Archaea, and viruses, to protists, Fungi, and other microbial Eukaryotes, to soil meso- and macrofauna community members, including Collembola, Nematoda, Arachnida, Insecta, and other small Metazoa. We observed a substantial, often gradual, re-structuring of the soil communities in the exclosure plots on multiple tropical and functional levels. For example, within the microbial food web, we observed decreased relative abundances of eukaryotic predators (e.g., ciliates) and bacterivorous bacteria (e.g., Myxococcota) after the long-term exclusion of herbivores, while relative abundances of viruses targeting Bacteria increased. Prominent changes in relative abundances of meso- and macrofauna community members after the long-term exclusion of herbivores were decreased relative abundances of Rhabditophora (Platyhelminthes), Monogononta (Rotifera), and Maxillopoda (Arthropoda) and increased relative abundance of Insecta and Arachnida (both Arthropoda). However, among eukaryotic kingdoms, Fungi showed the strongest positive response to the exclusion of herbivores and the subsequent increase of vascular plants. Especially the abundances of mycorrhizal fungi and plant pathogens were increased, coinciding with increased relative abundances of viruses targeting Fungi. Furthermore, with increasing coverage of vascular plants, soil respiration rates increased. At the same time, total microbial biomass did not differ significantly, but the turnover time of microbial biomass was significantly shorter 14 years after the exclusion of herbivores.
Taken together our results suggest that High-Arctic tundra ecosystems with a vascular-plant-dominated vegetation, here caused by changes in herbivore grazing pressure, are characterized by an altered soil food web, facilitating a faster microbial loop and an accelerated decomposition of soil organic matter. Thus, we demonstrated how aboveground changes substantially altered belowground communities and the trophic interactions that control carbon cycling in High-Arctic tundra ecosystems.
How to cite: Söllinger, A., Bender, K. M., Martin, V., Bjørdal, Y., Dahl, M. B., Richter, A., Loonen, M., Svenning, M. M., and Tveit, A. T.: Cascading effects of Arctic tundra herbivory on above- and belowground biomass, soil biogeochemistry, and soil (microbial) food webs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11566, https://doi.org/10.5194/egusphere-egu25-11566, 2025.
The fate of the soil organic matter stored in arctic ecosystems in a future warmer climate is highly debated but remains quite uncertain, especially as most studies do not take into account the combined effect of climate change and simultaneous invasion by non-native fauna. For example, while the impact of climate change on carbon losses from the arctic might be limited due to the strong nutrient limitations restricting microbial activity and decomposition speed in these ecosystems, the current invasion by burrowing earthworms as a result of human activity might alleviate the nutrient limitations and modify the soil food web, which could significantly increase carbon losses. We investigated the effect of burrowing earthworm addition on soil mesofauna and microbial community composition and on associated carbon stability of the arctic tundra by the end of a 4-year-long mesocosm experiment in northern Sweden. The abundance of collembola and oribatid mites was positively affected by earthworm addition in a heath-type tundra ecosystem, while no changes were detectable in a meadow-type tundra. This is surprising as the meadow-type tundra was strongly affected by earthworms in terms of soil structure with a decrease in total carbon stock. We tested the stability of the residual carbon by measuring CO2 emissions during an incubation of the organic and mineral soil horizons at current and increased temperatures. We found that while carbon stability is not clearly affected by earthworm addition in the heath-type tundra, the stability of the leftover carbon is increased in the presence of earthworms in the meadow-type tundra in the first 10 soil centimeters in both incubation temperatures. This suggests that the ultimate effect on carbon dynamics of earthworm invasion cannot be simply estimated from the immediate carbon loss from the organic layer, as the changes in carbon forms and quality could modify the future organic matter availability to decomposers.
How to cite: D'Hervilly, C., Blume-Werry, G., Krab, E., Jonsson, H., and Garamszegi, P.: Will invasive burrowing earthworms affect soil food web and carbon stability in arctic tundra?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11869, https://doi.org/10.5194/egusphere-egu25-11869, 2025.
With melting of permafrost many changes of arctic soils can be expected. Important changes are expected to be associated with invasion of soil ecosystem engineers such as earthworms and or other soil macrofauna. The effect of ecosystem engineers if context specific, not only in a way that environmental conditions such as soil texture, pH or litter quality may affect effect of engineers, but also in the way that ecosystem engineers change their environment which then alternate effect of engineers on the system. The latter effect made evaluation of engineer’s effect complex because it basically means that when we do simple manipulation experiment when we manipulate presence of engineers we can get different response to that manipulation in different stages of invasion of better to say after system has been modified by engineers for some time. This is due to the fact that previous effect of engineers leaves some legacy of long-term effects and this legacy change immediate effects of engineers. Here we focus on earthworm invasion/colonization. The aim of this contribution is to summarize our knowledge about changes of earthworm immediate effects on the soil along gradient of earthworm long term legacy in the system and formulate simple conceptual framework than may help to understood underlying mechanism of this phenomena, which may help in its implication to ongoing to future ecosystem invasions such as earthworm colonization of the arctic.
How to cite: Frouz, J.: The effect of ecosystem engineers invasion is context specific and depends of stage of invasion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6601, https://doi.org/10.5194/egusphere-egu25-6601, 2025.
Posters on site: Thu, 1 May, 16:15–18:00 | Hall X1
Cold season greenhouse gas (GHG) emissions have been found to make non-negligible contributions to annual carbon budgets in Arctic-boreal regions. The Arctic is warming three to four times faster than the global average, changing the magnitude and phase (snow/rain) of precipitation, and the thermal regimes of snow-covered ground.
Future projections of winter GHG emissions require accurate simulations of the insulative properties of Arctic snowpacks and improved parameterisations of soil heterotrophic respiration as a function of soil thermal and moisture regimes. To improve these parameterisations in terrestrial biospheric models, we measured carbon dioxide and methane fluxes through the late-winter snowpack of a mineral upland tundra site in the western Canadian Arctic. Fluxes were calculated using highly resolved GHG snow concentration gradients and vertical snowpack microstructure (n = 119), over a range of microtopographic and vegetation types.
GHG emission rates were statistically independent of vertical snow microstructures, suggesting high snow gas porosity relative to soil emission. Carbon dioxide emissions were measured across a wide range of tundra landscape types, and were closely linked to soil temperatures, vegetation type and snow depths. Importantly, persistent net methane sinks were also found across landcover types in warmer soils (-6 to -2 oC), showing active methane oxidation during winter periods. Methane emissions were not always consistent within surface cover types, suggesting available liquid soil moisture and carbon availability as important controls.
How to cite: Rutter, N., Hould Gosselin, G., Mann, P., Sonnentag, O., and Marsh, P.: Identifying Spatial Patterns in Greenhouse Gas Fluxes through an Arctic Tundra Snowpack , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12132, https://doi.org/10.5194/egusphere-egu25-12132, 2025.
Northern boreal forests are globally crucial sinks for atmospheric carbon dioxide (CO2) but, due to climate change, these sinks are at risk of switching to CO2 sources. Climate change affects winters for example by altering snow depth, with regional increases or decreases in snowfall. Since snow cover regulates key ecosystem processes in boreal forests, such changes may affect ecosystem functioning with possible consequences for CO2 exchange year-round. Climate change does not act alone but together with other factors such as herbivory. In boreal forests, reindeer (Rangifer tarandus L.; caribou in North America) is a key herbivore that affects understory vegetation — particularly lichen cover — which may, in turn, affect understory CO2 exchange. Yet, it remains largely unknown how the changing snow depth together with divergent reindeer grazing conditions affects CO2 exchange in the boreal forests.
To study these snow-grazer interactions on understory CO2 exchange, we conducted CO2 flux measurements during the snow-free season over four years in two Scots pine (Pinus sylvestris L.) forests in northern Fennoscandia. Using a manual chamber method, we measured CO2 exchange across snow depth manipulation treatments (i.e., ambient, reduced and increased snow depth) in areas of active reindeer grazing and adjacent areas where grazing had been excluded for 25 and 55 years.
We found that reduced and increased snow depths had opposing impacts on understory CO2 exchange, but only if reindeer had been excluded. Specifically, reduced snow depth increased the understory CO2 source strength while increased snow depth decreased it when reindeer had been excluded. In contrast, snow depth did not affect CO2 exchange in the presence of continuous reindeer grazing. These findings suggest that, in northern pine forests, changes in snow depth may unbalance the understory CO2 exchange with long-term reindeer absence. On the contrary, the presence of continuous reindeer grazing may enhance ecosystem resistance to changes in snow depth. We propose considering these snow-grazer interactions for accurate global C budget estimates in a changing winter climate in boreal forests.
How to cite: Kantola, N., Väisänen, M., Leffler, A. J., and Welker, J. M.: Does Reindeer Grazing Dictate Understory CO2 Exchange Responses to Snow Depth Changes in Boreal Forests?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16291, https://doi.org/10.5194/egusphere-egu25-16291, 2025.
Variations in snow depth are significantly altering the soil environment in the permafrost regions of the Tibetan Plateau, which in turn affects vegetation growth. However, how plant leaf and root traits and their relationship respond to increased snow depth remains unclear. Thus, the present study aimed to examine the influence of increased snow depth on plant growth and functional traits of leaf and root in the alpine meadow of the Tibet, exploring how plant above-ground and below-ground parts cascading responded to increased snow depth. This study employs snow fences to artificially increase snow depth and measures above-ground biomass, root biomass, specific leaf area (SLA), leaf carbon concentration (C), leaf nitrogen concentration (N), and leaf phosphorus concentration (P), specific root area (SRA), specific root length (SRL), root tissue density (RTD), root diameter (RD), root carbon concentration (C), root N concentration, and root P concentrations. Increased snow depth significantly increased root biomass compared to ambient controls, but didn’t change above-ground biomass. Increased snow depth significantly decreased SLA but increased leaf C, N and P concentrations. For root functional traits, increased snow depth increased SRL and SRA, but decreased RTD and AD. Effect size result showed that plant leaves was less affected by increased snow depth as compared with root. Particularly, leaf traits changed larger in physiological plasicity traits (leaf C, N, P cocentrations) as compared with morphological plasticity traits (AGB, SLA). In converse, root traits changed larger in morphological plasticity traits (BGB, SRL, SRA, RTD, RD) rather than physiological plasicity traits(root C, N, P cocentration). Principal component analysis showed that leaf functional traits are primarily driven by leaf C, N, and P concentrations, while root functional traits are mainly driven by morphological traits such as SRL, SRA, and RTD. The inconsistently respond of plant leaf and root to increased snow depth in the alpine meadow of the Tibetan Plateau suggested that trade-offs between above- and below- functions are necessary for plant to optimize resource use under changing environment. Our results also emphasize the importance of feedback between above- and below-ground plant traits to better understand plant community responses to future climate change.
How to cite: Yang, Y., Tan, X., and Zhang, J.: Inconsistent Responses of Above- and Below-ground to 8 Years Increased Snow Depth at the Alpine Meadow in the Permafrost Region of the Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-284, https://doi.org/10.5194/egusphere-egu25-284, 2025.
Due to the above global average warming, the winter climate in West Greenland is increasingly characterized by warm spells causing snow melt and soil exposure. These events might activate soil microbes and associated nutrient cycles, with consequences for the tundra ecosystem, even in the following summer.
Here we studied effects of winter warming in a dry heath tundra ecosystem in Blæsedalen on Disko Island, West Greenland near Arctic Station, characterized by low shrub vegetation (Betula nana, Salix glauca, Vaccinium uliginosum, Empetrum nigrum, Cassiope tetragona). We established replicate 0.5 m2 plots equipped with custom-made heating probes that were pre-installed in the growing season aiming to warm up the surrounding soil in the following winter campaign to a depth of 15 cm during a week. Nitrogen (N) transformation pathways from organic N (proteins and amino acids) to ammonium (inorganic N) and microbial N uptake were quantified in the tundra soil using 15N labelling techniques, accompanied by greenhouse gas flux measurements.
In situ warming resulted in soil CO2 loss, and activated microbial CH4 uptake. Under laboratory conditions, we could also detect several freeze-thaw induced emission peaks of N2O and N2. For the first time nanoSIMS analysis revealed rapid soil microbial uptake of amino acid alanine into microbial cells in winter soils. Furthermore, optical microscopy and Raman spectroscopy analysis of microbial communities provided insights into both their immediate response to the warming and into memory effects in the following growing season, with increased microbial activity in the samples taken from plots that have been warmed.
In sum, we highlight a fast activation of microbial N turnover due to Arctic winter warming events, which results in changes in nutrient cycling that persist in the following growing season.
How to cite: Rütting, L., Rodas, S., Klinghammer, F., Ranjbari, E., Micaroni, M., Rasmussen, L. H., Elberling, B., Danielsen, B. K., Patchett, A., Rütting, T., de Jong, G. F., Dannenmann, M., Ramm, E., Platakyte, R., Björkman, M., Zou, H., Arellano, C., Pucetaite, M., and Hammer, E. C.: Microbial nitrogen uptake in winter warming manipulation experiments in Arctic tundra (Disko Island; Greenland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12968, https://doi.org/10.5194/egusphere-egu25-12968, 2025.
Phacidium infestans Karsten DSM 5139 is a significant fungal pathogen that causes snow blight in conifers across Europe and Asia. Thriving under snow cover, P. infestans infects and kills pine needles, which are known for their antifungal properties. The genome of the strain DSM 5139 was sequenced using PacBio II technology, resulting in 44 contigs with a genome size of ~36.8 Mb and a GC content of 46.4%. Genome completeness was assessed at 98.6% using BUSCO analysis, and its annotation revealed 11,357 open reading frames. Functional annotation identified 573 carbohydrate-active enzymes and approximately 400 genes linked to secondary metabolite biosynthesis.
Several mechanisms facilitating P. infestans survival and proliferation on pine needles were identified, including drug-efflux pumps, acyclic terpene synthases, and phytoalexin detoxification enzymes. Two cutinase proteins were detected. Their protein modeling confirmed the presence of functional structures such as signal peptides, catalytic triads, and lid domains. In addition, numerous cold-survival strategies were identified including trehalose synthesis enzymes, desaturases, stress response proteins, and two ice-binding proteins that modulate ice crystal formation at subzero temperatures.
Pathway reconstruction revealed an efficient nutrient acquisition strategy. First, the fungus breaches the needle waxes using secreted cutinases. Then it degrades the plant cell wall polymers with cellulases, pectinases, lignin-degrading enzymes, and other plant cell wall-degrading enzymes.
This study represents one of the first comprehensive genomic analyses of P. infestans, providing valuable insights into its genomic adaptations for nutrient acquisition and survival in cold environments. The findings enhance our understanding of fungal-plant interactions and highlight the ecosystem functioning of this fungal pathogen in forest ecosystems.
How to cite: Zerouki, C., Kuittinen, S., Pappinen, A., and Turunen, O.: Genomic and Proteomic Analysis of Functional Genes in Phacidium infestans DSM 5139 for Nutrient Acquisition and Ecosystem Functioning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3611, https://doi.org/10.5194/egusphere-egu25-3611, 2025.
Arctic wildfires disrupt biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), which challenges exposed tundra ecosystems. In this study, we investigated the legacy of variable fire intensity on soil microbial nutrient cycling in field experiments on Disko Island, West Greenland, three years post-fire. Despite finding no significant differences in gross N mineralization and consumption rates, high-intensity fire-treated soil microbes exhibited reduced degradation of a protein substrate in soil chips, suggesting altered microbial activity in organic N cycling pathways. These results highlight the return of some biogeochemical processes over time, and also reveal potential vulnerabilities in microbial communities and their functionality in legacy after high-intensity fire. As fire frequency in the Arctic is expected to increase due to climate change, long-term consequences for ecosystems may include shifts in microbial composition and nutrient cycling, and slow ecosystem recovery. The feedback could alter greenhouse gas emissions, accelerate permafrost thaw and cause ecosystem transformation. Understanding these processes is critical for predicting the wider ecological effects of more frequent and intense fires. Future research should focus on multi-temporal sampling and microbial dynamics to better capture fire-induced alterations and their cascading effects on Arctic ecosystems and global climate regulation.
How to cite: Rodas, S., Arellano, C., Hammer, E. C., Zou, H., Klingammer, F., Ambus, P., and Rütting, L.: Arctic tundra soil microbiology retained effects from controlled in situ fire after 3 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15164, https://doi.org/10.5194/egusphere-egu25-15164, 2025.
Permafrost soils are devoid of fauna while frozen, but little is known about how fauna affects their biogeochemistry upon thawing. Most soil fauna resides in the uppermost layers of the soil, and are therefore unlikely to colonize deep, often anoxic, soils at the bottom of the active layer where newly-thawed permafrost is found. However, abrupt thaw events can result in newly-thawed permafrost being exposed to the surface, and such events are both common throughout the circum-Arctic and an important uncertainty in permafrost biogeochemistry. While the exact faunal dispersal mechanisms remain unexplored, literature suggests that surrounding soil fauna can migrate into newly-thawed permafrost within a year after an abrupt thaw event.
To date, we have no information on whether the introduction of soil fauna alters the biogeochemical functioning of permafrost soils: most mechanistic studies are carried out with permafrost soil thawed in vitro, into which fauna has no chance of dispersing, while plot- or ecosystem-level measurement do not distinguish between faunal and microbial activity. Simple questions, such as whether the presence of soil fauna alters the microbial production of greenhouse gases, remain untested, in part due to a lack of appropriate methodology. Here we introduce isotopic partitioning of faunal (model Collembola Folsomia candida) and microbial CO2 production in permafrost and active layer soil from a sub-arctic palsa peatland. Whole-organism isotopic enrichment coupled with 13C-CO2 measurement allows us to test whether faunal presence primes microbial respiration. This method can be expanded both to other soil organisms and greenhouse gases, and thus represents a promising avenue towards a quantitative understanding of biotic interactions in newly-thawed permafrost soils.
How to cite: Monteux, S., Dorrepaal, E., and Krab, E.: Does soil fauna prime microbial respiration in permafrost?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9866, https://doi.org/10.5194/egusphere-egu25-9866, 2025.
Surface microbial communities on the Greenland Ice Sheet play a vital role in modulating glacier surface melt by altering surface albedo through extensive algal blooms. The potential for extended melt season through a changing climate bears the fuel for microbial bloom expansion. However, the mechanisms governing bloom density and distribution, including the roles of microbially produced signalling and defensive compounds, remain poorly understood. This study investigates intracellular metabolic changes in supraglacial microbial communities under environmental stress to uncover factors regulating bloom dynamics and cell-to-cell communication. We employed high-resolution mass spectrometry (HRMS) to identify intracellular microbial secondary metabolites with ecological functions. The endometabolome composition was analysed to assess its response to abiotic stressors such as different light, pH, salinity and temperature conditions and its role in modulating bloom dynamics. Results indicate that light intensity strongly impacts supraglacial microbial communities' metabolic profiles, highlighting light conditions as a key driver of their ecological fitness. Our findings contribute to an expanding database of microbial metabolites and offer insights into the chemical diversity of glacier ecosystems in oligotrophic extreme environments.
How to cite: Morische, A., Bolander Jensen, M., Larsson, Y., Bester, K., Benning, L. G., Tranter, M., and Anesio, A. M.: Stress-Induced Shifts in Endometabolome Composition Reveal Microbial Adaptations on Glacier Surfaces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18311, https://doi.org/10.5194/egusphere-egu25-18311, 2025.
Soil microbial metabolism is extremely important to large scale processes such as nutrient cycling and climate change. At the same time, the changing climate influences soil structure and function, especially in the Arctic region, which has been experiencing faster and more intense warming compared to anywhere else in the world. To better understand the microscale processes and how they are affected by changing temperatures and extreme weather events, we use soil microchips, mimicking the soil structure and providing visual access to the soil systems, and incubate them with microorganisms from Arctic biological soil crusts. These chips then are subjected to different freezing and thawing cycles (FTCs), and we follow the microbial activity and metabolism by the means of optical microscopy and Raman microspectroscopy.
The samples for this experiment were collected in summer from a dry heath tundra ecosystem in Blæsedalen on Disko Island, West Greenland. The plots where the soil was sampled had been warmed during the previous winter in a winter warming experiment which showed some increased activity of microbes from the warmed plots. During the laboratory experiments, the chips containing soil microbes were placed at +5 °C (control), as well as -5 °C and -18 °C (freezing) temperatures. The frozen chips were thawed at two different frequencies – one daily and one biweekly. During the six weeks of the freezing and thawing cycles, the chips were observed in an optical microscope in order to follow the microbial growth and community changes. After the treatment was finished, the chips were analysed by Raman microspectroscopy.
Raman microspectroscopy can be employed to study the chemical composition and metabolic processes of individual live microorganisms in near real time. The microbial metabolic activity was monitored using SIP (stable isotope probing) Raman microspectroscopy. We injected SIP labelled substrates into the soil microchips and followed the intensity of SIP related spectral bands as microorganisms incorporated the labelled substances. The results show significant differences between control and FTC treatment chips, with microbes from control chips metabolizing injected substances much faster, especially in the case of bacteria. The differences among the treated chips are less pronounced. However, the microbes in the chips that had been thawed daily exhibit stronger fluorescence signal, suggesting their different protective responses to the stronger environmental stressor.
All in all, soil chips allow the visual observation of microbial community changes in response to FTCs, while SIP Raman makes it possible to estimate metabolic activity rates of individual organism groups. Although currently limited in scale, in the future this information could be used to better describe the role of microbial communities in larger scale climate models.
How to cite: Platakyte, R., Rütting, L., Björkman, M., Hammer, E., and Pucetaite, M.: Effects of intense freeze-thaw cycles on Arctic biological soil crusts as studied by Raman microspectroscopy , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9255, https://doi.org/10.5194/egusphere-egu25-9255, 2025.
Organic and inorganic materials from atmospheric, aeolian, and subglacial origins on glacier surfaces are colonized by microorganisms, which produce extracellular polymeric substances to bind them into cohesive aggregates known as cryoconite. Dispersed across the glacier surface, these biologically active particulates may form cylindrical cryoconite holes through localized melting driven by their dark coloration, which strongly reduces surface albedo. Dispersed cryoconite serves as both a precursor and a transitional stage in the lifecycle of cryoconite holes, which can collapse and reform multiple times during the melting season. While cryoconite holes provide a stable environment that shields microbial communities from environmental extremes, dispersed cryoconite is exposed to intense solar irradiance, freezing temperatures, and desiccation. This contrast in environmental conditions experienced by the same material is hypothesized to significantly impact the microbial dynamics and ecological functioning of cryoconite.
In this study, we investigated the cryoconite microbiome from both cryoconite holes and dispersed cryoconite collected approximately 1 km from the margin of the Greenland Ice Sheet. By comparing the microbial communities in these two environments, we aimed to understand differences in their composition and diversity. Amplicon sequencing targeting the V3–V4 region of the 16S rRNA gene was applied to capture bacterial diversity directly from raw samples and cultured communities grown under various conditions, providing insights into both the overall bacterial composition and the subset of microbes that can be cultured.
We found that species diversity and evenness were significantly higher in dispersed cryoconite than in cryoconite holes, whereas species richness remained unaffected. The microbial composition also differed, with cryoconite holes exhibiting higher relative abundances of Proteobacteria and Actinobacteria, and a lower abundance of Cyanobacteria compared to dispersed cryoconite. Differential abundance analysis revealed significant enrichment of certain taxa in each environment, including several Cyanobacteria-associated taxa that were nearly absent in cryoconite holes but abundant in dispersed cryoconite. This contrast suggests that these Cyanobacteria may have developed advanced stress-adaptation strategies that may give them an advantage over other microorganisms in dispersed cryoconite, whereas their near absence in cryoconite holes could be driven by higher predation or other ecological pressures.
In summary, these findings underscore differences in microbial diversity between cryoconite holes and dispersed cryoconite, indicating that distinct environmental pressures may shape their microbial communities. By highlighting key differences in community composition, this work lays a foundation for future research into the broader microbial dynamics and ecological functions of cryoconite in polar environments. Further research is needed to elucidate the specific roles and succession dynamics of key taxa, such as Cyanobacteria.
How to cite: van Dijk, L.: Microbial Diversity in Cryoconite Holes and Dispersed Cryoconite Revealed Through Culture-Dependent and Culture-Independent Approaches, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17205, https://doi.org/10.5194/egusphere-egu25-17205, 2025.
