Future emergence of new ecosystems caused by glacial retreat

Plants' Contributions to People Shift With Glacier Extinction

Alpine environments are among the most vulnerable ecosystems to climate change, with glacier retreat rapidly altering plant communities, biodiversity, and ecosystem functions. However, the socio-economic consequences of these biodiversity changes remain largely unexplored. Understanding Nature's Contributions to People (NCP) provides a valuable framework for assessing biodiversity's role in human well-being. While NCP has typically been studied at the landscape level, we focus on species-specific contributions of plants to highlight the importance of glacial biodiversity for people. Our novel concept of Plants' Contributions to People (PCP) provides insights into the ecological, social, and economic significance of plant biodiversity and offers a practical approach for guiding conservation efforts and policy decisions. We surveyed 99 plant species in four glacier environments in the Italian Alps; one glacier (Trobio) underwent a complete extinction in 2023 while another glacier (Amola) has a widespread surface debris cover and is proximate to extinction. We then grouped plant species into early, intermediate, and late depending on their successional stages, and then linked plants to 13 different PCP based on extensive literature research. By comparing present and projected future scenarios, we assessed the absolute and relative changes in PCP under glacier extinction. Our results show that changes in PCP are primarily driven by declining plant species richness. Most affected PCP are associated with air quality, soil health, and nutrient regulation, which decrease by sevenfold on average across plant species. Whereas natural hazards regulation showed no significant variation, association with pest and disease increases especially for late species. While future plant communities may provide PCP that are qualitatively similar to present-day communities, the volume of species-specific contributions would decrease due to biodiversity loss associated with glacier extinction. Our results provide the first evidence of PCP shift toward erosion following a decrease in plant species richness. This case study demonstrates that PCP is a valuable tool for assessing the ecological and socio-economic consequences of biodiversity change, helping raise awareness of the biodiversity crisis and inform conservation actions aimed at sustaining ecosystem functions in a rapidly changing world.

Mercury Transport, Transformation and Accumulation Recorded by Stable Isotopes during Retreated Glacier Chronosequence of 250 Years

Vegetative development in regions where glaciers retreated due to global warming forces the mercury (Hg) cycle in the cryosphere. This study depicts the fate of Hg in a glacier-retreated chronosequence over the last 250 years recorded by signals of stable Hg isotopes. Results show that the Hg storage in surface soil increases by 3.2 times over 250 years after the glacier retreated. 53 ± 11% of Hg in grass shoots is from the uptake of atmospheric Hg0 and 47 ± 11%, from the uptake of soil Hg. Atmospheric Hg2+ is the primary source of surface soil Hg (54 ± 13%), followed by atmospheric Hg0 (40 ± 10%) and geogenic Hg. The Hg accumulation in soils increased by a factor of 5 at an accelerating rate from the 1870s to 2010s. The Hg release flux from melting glaciers is 3.51 ± 0.01 μg m-2 yr-1. The highly positive Δ199Hg (1.03 ± 0.49‰) in precipitation due to photoreduction of Hg2+ in water droplets causes all samples in ecosystems to have positive Δ199Hg values. Isotopic evidence suggests that photolytic and abiotic dark reduction processes have driven Hg0 re-emission from glacier and underlying soil after melting. The accelerated Hg release from melting glaciers and soil Hg accumulation caused by global warming alter Hg cycling in the cryosphere.

Environmental consequences of interacting effects of changes in stratospheric ozone, ultraviolet radiation, and climate: UNEP Environmental Effects Assessment Panel, Update 2024

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) addresses the interacting effects of changes in stratospheric ozone, solar ultraviolet (UV) radiation, and climate on the environment and human health. These include new modelling studies that confirm the benefits of the Montreal Protocol in protecting the stratospheric ozone layer and its role in maintaining a stable climate, both at low and high latitudes. We also provide an update on projected levels of solar UV-radiation during the twenty-first century. Potential environmental consequences of climate intervention scenarios are also briefly discussed, illustrating the large uncertainties of, for example, Stratospheric Aerosol Injection (SAI). Modelling studies predict that, although SAI would cool the Earth's surface, other climate factors would be affected, including stratospheric ozone depletion and precipitation patterns. The contribution to global warming of replacements for ozone-depleting substances (ODS) are assessed. With respect to the breakdown products of chemicals under the purview of the Montreal Protocol, the risks to ecosystem and human health from the formation of trifluoroacetic acid (TFA) as a degradation product of ODS replacements are currently de minimis. UV-radiation and climate change continue to have complex interactive effects on the environment due largely to human activities. UV-radiation, other weathering factors, and microbial action contribute significantly to the breakdown of plastic waste in the environment, and in affecting transport, fate, and toxicity of the plastics in terrestrial and aquatic ecosystems, and the atmosphere. Sustainability demands continue to drive industry innovations to mitigate environmental consequences of the use and disposal of plastic and plastic-containing materials. Terrestrial ecosystems in alpine and polar environments are increasingly being exposed to enhanced UV-radiation due to earlier seasonal snow and ice melt because of climate warming and extended periods of ozone depletion. Solar radiation, including UV-radiation, also contributes to the decomposition of dead plant material, which affects nutrient cycling, carbon storage, emission of greenhouse gases, and soil fertility. In aquatic ecosystems, loss of ice cover is increasing the area of polar oceans exposed to UV-radiation with possible negative effects on phytoplankton productivity. However, modelling studies of Arctic Ocean circulation suggests that phytoplankton are circulating to progressively deeper ocean layers with less UV irradiation. Human health is also modified by climate change and behaviour patterns, resulting in changes in exposure to UV-radiation with harmful or beneficial effects depending on conditions and skin type. For example, incidence of melanoma has been associated with increased air temperature, which affects time spent outdoors and thus exposure to UV-radiation. Overall, implementation of the Montreal Protocol and its Amendments has mitigated the deleterious effects of high levels of UV-radiation and global warming for both environmental and human health.

The GlaMBIE Team, Zemp M, Jakob L, Dussaillant I, Nussbaumer SU, Gourmelen N, Dubber S, A G, Abdullahi S, Andreassen LM, Berthier E, Bhattacharya A, Blazquez A, Boehm Vock LF, Bolch T, Box J, Braun MH, Brun F, Cicero E, Colgan W, Eckert N, Farinotti D, Florentine C, Floricioiu D, Gardner A, Harig C, Hassan J, Hugonnet R, Huss M, Jóhannesson T, Liang CCA, Ke CQ, Khan SA, King O, Kneib M, Krieger L, Maussion F, Mattea E, McNabb R, Menounos B, Miles E, Moholdt G, Nilsson J, Pálsson F, Pfeffer J, Piermattei L, Plummer S, Richter A, Sasgen I, Schuster L, Seehaus T, Shen X, Sommer C, Sutterley T, Treichler D, Velicogna I, Wouters B, Zekollari H, Zheng W. Community estimate of global glacier mass changes from 2000 to 2023

Glaciers are indicators of ongoing anthropogenic climate change1. Their melting leads to increased local geohazards2, and impacts marine3 and terrestrial4,5 ecosystems, regional freshwater resources6, and both global water and energy cycles7,8. Together with the Greenland and Antarctic ice sheets, glaciers are essential drivers of present9,10 and future11-13 sea-level rise. Previous assessments of global glacier mass changes have been hampered by spatial and temporal limitations and the heterogeneity of existing data series14-16. Here we show in an intercomparison exercise that glaciers worldwide lost 273 ± 16 gigatonnes in mass annually from 2000 to 2023, with an increase of 36 ± 10% from the first (2000-2011) to the second (2012-2023) half of the period. Since 2000, glaciers have lost between 2% and 39% of their ice regionally and about 5% globally. Glacier mass loss is about 18% larger than the loss from the Greenland Ice Sheet and more than twice that from the Antarctic Ice Sheet17. Our results arise from a scientific community effort to collect, homogenize, combine and analyse glacier mass changes from in situ and remote-sensing observations. Although our estimates are in agreement with findings from previous assessments14-16 at a global scale, we found some large regional deviations owing to systematic differences among observation methods. Our results provide a refined baseline for better understanding observational differences and for calibrating model ensembles12,16,18, which will help to narrow projection uncertainty for the twenty-first century11,12,18.

Dissemination of genes associated with antibiotic resistance and bacterial virulence during ecosystem succession in two Tibetan glacier forefields

The release of pathogens and DNA from the cryosphere (glacier, permafrost, and, sea ice) has become a new threat to society and environment. Due to enhanced glacier retreat, the size of glacier forefields has greatly expanded. Herein, we used a combination of metagenomic and metatranscriptomic methods and adopted a sequence-based approach to investigate the distribution and changing patterns of virulence factor genes (VFGs) and antibiotic resistance genes (ARGs) in two glacier forefields. The forefields are separated by approximately 400 km located in the center and north of the Tibetan Plateau, which are used to demonstrate the gene dissemination capacity across short (10 m) and long (730 m) spatial transects. The results revealed a diverse range of actively transcribed VFGs and ARGs. The relative abundance of ARG reduced with ecosystem succession, while that of VFG was similar, suggesting that the ARG is under a stronger environmental selection pressure. VFGs and ARGs were dominated by those associated with adherence and vancomycin resistance, respectively. Notably, toxin production related genes were identified but a low abundance, indicating a low risk to health in glacier forefields. The dissemination risks were low for both VFGs and ARGs, which was strongly constrained by dispersal limitation. Additionally, the limited dissemination was mainly through vertical transmission, instead of horizontal transfer. In conclusion, the sequence-based approach revealed a low risk to health in recently deglaciated areas, with the risk of VFGs and ARGs being disseminated into downstream ecosystems remaining low.

High-resolution assessment of climate change impacts on the surface energy and water balance in the glaciated Naryn River basin, Central Asia

Mountain regions of Central Asia are experiencing strong influences from climate change, with significant reductions in snow cover and glacial reserves. A comprehensive assessment of the potential consequences under the worst-case climate scenario is vital for adaptation measures throughout the region. Water balance analysis in the Naryn River basin was conducted for the baseline period of 1981-2000 including potential changes under the worst-case SSP5-8.5 scenario for 2077-2096 by combining high-resolution (5 km) regional climate projections with fully distributed glacio-hydrological (1 km) modeling. Results showed that with the complete degradation of glaciers and increase in evapotranspiration, the overall runoff will decrease by 16%, and in the upper basins, the reduction will exceed 40%. The maximum snow water equivalent (SWE) is projected to decrease by 17%, and the seasonal peak of SWE will occur one month earlier. The transition from snow to rain will significantly affect lower regions, increasing extremes in peak runoff and causing 10-year recurrence interval events to occur every 3-4 years. Moreover, extreme runoff in high mountainous areas will increase due to intensified snowmelt and increased rainfall extremes. Additionally, a gradient of surface soil temperature change of 0.1 °C per 100 m elevation gain was observed, suggesting a potential snow-albedo feedback effect that could further amplify the warming, especially at higher altitudes. This study provides a robust analytical framework to assess the complex responses of mountain ecosystems to the impacts of climate change, with the potential of widespread application for addressing the challenges facing these critical regions.

Ecological interactions in glacier environments: a review of studies on a model Alpine glacier

Glaciers host a variety of cold-adapted taxa, many of which have not yet been described. Interactions among glacier organisms are even less clear. Understanding ecological interactions is crucial to unravelling the functioning of glacier ecosystems, particularly in light of current glacier retreat. Through a review of the existing literature, we aim to provide a first overview of the biodiversity, primary production, trophic networks, and matter flow of a glacier ecosystem. We use the Forni Glacier (Central Italian Alps) - one of the best studied alpine glaciers in the world - as a model system for our literature review and integrate additional original data. We reveal the importance of allochthonous organic matter inputs, of Cyanobacteria and eukaryotic green algae in primary production, and the key role of springtails (Vertagopus glacialis) on the glacier surface in sustaining populations of two apex terrestrial predators: Nebria castanea (Coleoptera: Carabidae) and Pardosa saturatior (Araneae: Lycosidae). The cryophilic tardigrade Cryobiotus klebelsbergi is the apex consumer in cryoconite holes. This short food web highlights the fragility of nodes represented by invertebrates, contrasting with structured microbial communities in all glacier habitats. Although further research is necessary to quantify the ecological interactions of glacier organisms, this review summarises and integrates existing knowledge about the ecological processes on alpine glaciers and supports the importance of glacier-adapted organisms in providing ecosystem services.

Wild Andean camelids promote rapid ecosystem development after glacier retreat

Knowing mechanisms that facilitate the emergence of post-glacial ecosystems is urgently required given rapid recent glacial retreat in high latitude and high elevation regions. We examined the effect of nutrient hotspots created via communal dung deposition by wild, native Andean camelids on soil abiotic and biotic properties and plant cover in the rapidly deglaciating Cordillera Vilcanota, southeastern Peru. Animal-modified proglacial soils were significantly enriched in all measured edaphic properties compared to reference glacial-till soils of the same age adjacent to animal-modified soil patches. Organic matter composition, soil moisture, available inorganic nitrogen, and plant cover were nearly zero in glacial-moraine reference soils, but were at least one order of magnitude greater in animal-modified soils. Likewise, DNA concentrations were almost two orders of magnitude higher in modified soils (23 ± 9 µg DNA g soil-1) compared to reference soils (0.6 ± 0.3 µg DNA g soil-1). Animal-modified soil microbial community composition differed significantly from reference soils for both prokaryotes and eukaryotes, and eukaryote ASV richness was significantly higher in camelid latrines than in controls. Nutrient transfer into glacier forefields by native camelids shortcuts a 100+ year lag between glacier retreat and primary succession. Our results suggest that nutrient transfer into glacier forefields by wild, native animals may be an important, natural mechanism by which tropical Andean species can expand upslope at a pace relevant to climate change.

(Dis)connecting the Globe Through Water-Driven Ecological and Biogeochemical Corridors in the Polar-Alpine Biome

Global change is causing the melting of ice masses, permafrost thawing, and the shrinking of glaciers, thereby reshaping nature's rhythms. Longer thaw phases and more frequent dry periods are transforming water-driven transitional ecosystems (e.g., glacier-fed streams) in the Polar-Alpine biome. This shift risks replacing unique, specialist species with more generalist ones, leading to "biotic homogenization"-a loss of diversity that reduces ecosystems' adaptability to change. While more species may be present at local levels, this often comes at the expense of the critical roles that specialists play. These changes disrupt nature's balance and the provision of vital ecosystem services.

Functional changes of protist communities in soil after glacier retreat

Soil hosts key components of terrestrial biodiversity providing essential services to the below- and above-ground ecosystems. The worldwide retreat of glaciers is exposing new deglaciated terrains, offering a unique opportunity to understand the development of soil ecosystems under a changing climate. Many studies have investigated how biotic communities change after deglaciation, but protists have often been overlooked despite their key role in multiple ecosystem functions. Here, we aim to understand how protist communities develop along glacier forelands, describing their successional trajectories. Protist communities were characterized in 1251 soil samples from 46 glacier forelands across four continents. We used environmental DNA metabarcoding to identify the Molecular Operational Taxonomic Units (MOTUs) of protists based on a universal eukaryotic marker. The detected MOTUs were combined with information on multiple traits to assess how the functional diversity and composition of protist communities vary through time. Immediately after glacier retreat, protist communities are like those of polar and high-altitude habitats, with consumers being the dominant trophic group, followed by a relevant presence of phototrophs, while parasites were underrepresented. Over the succession, we detected an increase in taxonomic and functional diversity, but some highly specialized groups (e.g. phototrophic algae) declined. The use of a trait-based approach allowed us to identify distinct successional patterns depending on functional groups. Through the functional characterization of a crucial but understudied component of soil biotic communities, our study added one of the final pieces needed to predict how soil ecosystems will develop in the rapidly changing environment of glacier forelands.

Characteristics of methane and carbon dioxide in ice caves at a high-mountain glacier of China

The exploration of the spatiotemporal distribution of greenhouse gas (GHG) exchange in the cryosphere (including ice sheet, glaciers, and permafrost) is important for understanding its future feedback to the atmosphere. Mountain glaciers and ice sheets may be potential sources of GHG emissions, but the magnitude and distribution of GHG emissions from glaciers and ice sheets remain unclear because observation data are lacking. In this study, in situ CH4 and CO2 and the mixing ratios of their carbon isotope signatures in the air inside an ice cave were measured, and CH4 and CO2 exchange in the meltwater of Laohugou glacier No. 12, a high-mountain glacier in an arid region of western China, was also analyzed and compared with the exchange in downstream rivers and a reservoir. The results indicated elevated CH4 mixing ratios (up to 5.7 ppm) and depleted CO2 (down to 168 ppm) in the ice cave, compared to ambient levels during field observations. The CH4 and CO2 fluxes in surface meltwater of the glacier were extremely low compared with their fluxes in rivers from the Tibetan Plateau (TP). CH4 and CO2 mixing ratios in the air inside the ice cave were mainly controlled by local meteorological conditions (air temperature, wind speed and direction) and meltwater runoff. The carbon isotopic compositions of CH4 and CO2 in the ice cave and terminus meltwater indicated δ13C-CH4 depletion compared to ambient air, suggesting an acetate fermentation pathway. The abundances of key genes for methanogenic archaea/genes encoding methyl coenzyme M reductase further indicated the production of CH4 by methanogenic archaea from the subglacial meltwater of high-mountain glaciers. The discovery of CH4 emissions from even small high-mountain glaciers indicates a more prevalent characteristic of glaciers to produce and release CH4 from the subglacial environment than previously believed. Nevertheless, further research is required to understand the relationship between this phenomenon and glacial dynamics in the third pole.

The development of terrestrial ecosystems emerging after glacier retreat

The global retreat of glaciers is dramatically altering mountain and high-latitude landscapes, with new ecosystems developing from apparently barren substrates1-4. The study of these emerging ecosystems is critical to understanding how climate change interacts with microhabitat and biotic communities and determines the future of ice-free terrains1,5. Here, using a comprehensive characterization of ecosystems (soil properties, microclimate, productivity and biodiversity by environmental DNA metabarcoding6) across 46 proglacial landscapes worldwide, we found that all the environmental properties change with time since glaciers retreated, and that temperature modulates the accumulation of soil nutrients. The richness of bacteria, fungi, plants and animals increases with time since deglaciation, but their temporal patterns differ. Microorganisms colonized most rapidly in the first decades after glacier retreat, whereas most macroorganisms took longer. Increased habitat suitability, growing complexity of biotic interactions and temporal colonization all contribute to the increase in biodiversity over time. These processes also modify community composition for all the groups of organisms. Plant communities show positive links with all other biodiversity components and have a key role in ecosystem development. These unifying patterns provide new insights into the early dynamics of deglaciated terrains and highlight the need for integrated surveillance of their multiple environmental properties5.

Polyethylene glycol-polyvinylidene fluoride/TiO2 nanocomposite polymer coatings with efficient antifouling strategies: Hydrophilized defensive surface and stable capacitive deionization

Capacitive deionization (CDI) is flourishing as an energy-efficient and cost-effective water desalination method. However, challenges such as electrode degradation and fouling have hindered the practical deployment of CDI technology. To address these challenges, the key point of our strategy is applying a hydrophilic coating composed of polyethylene glycol (PEG)-functionalized nano-TiO2/polyvinylidene fluoride (PVDF) to the electrode interface (labeled as APPT electrode). The PEG/PVDF/TiO2 layer not only mitigates the co-ion depletion, but also imparts the activated carbon (AC) electrode hydrophilicity. As anticipated, the APPT electrode possessed an enhanced desalination capacity of 83.54 μmol g-1 and a low energy consumption of 17.99 Wh m-3 in 10 mM sodium chloride solution compared with the bare AC electrode. Notably, the APPT maintained about 93.19 % of its desalination capacity after 50 consecutive adsorption-desorption cycles in the presence of bovine serum albumin (BSA). During the trial, moreover, no obvious overall performance decline was noted in concentration reduction (Δc), water recovery (WR) and productivity (P) over 50 cycles. This strategy realizes energy-efficient, antifouling and stable brackish water desalination and has great promise for practical applications.

Priority effects transcend scales and disciplines in biology

Although primarily studied through the lens of community ecology, phenomena consistent with priority effects appear to be widespread across many different scenarios spanning a broad range of spatial, temporal, and biological scales. However, communication between these research fields is inconsistent and has resulted in a fragmented co-citation landscape, likely due to the diversity of terms used to refer to priority effects across these fields. We review these related terms, and the biological contexts in which they are used, to facilitate greater cross-disciplinary cohesion in research on priority effects. In breaking down these semantic barriers, we aim to provide a framework to better understand the conditions and mechanisms of priority effects, and their consequences across spatial and temporal scales.

Dynamics and drivers of mycorrhizal fungi after glacier retreat

The development of terrestrial ecosystems depends greatly on plant mutualists such as mycorrhizal fungi. The global retreat of glaciers exposes nutrient-poor substrates in extreme environments and provides a unique opportunity to study early successions of mycorrhizal fungi by assessing their dynamics and drivers. We combined environmental DNA metabarcoding and measurements of local conditions to assess the succession of mycorrhizal communities during soil development in 46 glacier forelands around the globe, testing whether dynamics and drivers differ between mycorrhizal types. Mycorrhizal fungi colonized deglaciated areas very quickly (< 10 yr), with arbuscular mycorrhizal fungi tending to become more diverse through time compared to ectomycorrhizal fungi. Both alpha- and beta-diversity of arbuscular mycorrhizal fungi were significantly related to time since glacier retreat and plant communities, while microclimate and primary productivity were more important for ectomycorrhizal fungi. The richness and composition of mycorrhizal communities were also significantly explained by soil chemistry, highlighting the importance of microhabitat for community dynamics. The acceleration of ice melt and the modifications of microclimate forecasted by climate change scenarios are expected to impact the diversity of mycorrhizal partners. These changes could alter the interactions underlying biotic colonization and belowground-aboveground linkages, with multifaceted impacts on soil development and associated ecological processes.

The distinctive weathering crust habitat of a High Arctic glacier comprises discrete microbial micro-habitats

Sunlight penetrates the ice surfaces of glaciers and ice sheets, forming a water-bearing porous ice matrix known as the weathering crust. This crust is home to a significant microbial community. Despite the potential implications of microbial processes in the weathering crust for glacial melting, biogeochemical cycles, and downstream ecosystems, there have been few explorations of its microbial communities. In our study, we used 16S rRNA gene sequencing and shotgun metagenomics of a Svalbard glacier surface catchment to characterise the microbial communities within the weathering crust, their origins and destinies, and the functional potential of the weathering crust metagenome. Our findings reveal that the bacterial community in the weathering crust is distinct from those in upstream and downstream habitats. However, it comprises two separate micro-habitats, each with different taxa and functional categories. The interstitial porewater is dominated by Polaromonas, influenced by the transfer of snowmelt, and exported via meltwater channels. In contrast, the ice matrix is dominated by Hymenobacter, and its metagenome exhibits a diverse range of functional adaptations. Given that the global weathering crust area and the subsequent release of microbes from it are strongly responsive to climate projections for the rest of the century, our results underscore the pressing need to integrate the microbiome of the weathering crust with other communities and processes in glacial ecosystems.

Hydrochemistry dynamics in a glacierized headwater catchment of Lhasa River, Tibetan Plateau

Mountain glaciers are essential for supplying water resources that sustain downstream communities and livelihoods, yet the hydrogeochemical dynamics at glacier terminals and the impact of glacier retreat on downstream water chemistry are not fully understood. This study addresses this by conducting comprehensive observations and analysis of water chemistry at refined spatial and temporal resolutions in the Lhasa River Valley Glacier No. 1 (LRVG-1) catchment, a vital source of drinking and irrigation water for the local population on the Tibetan Plateau. Our findings reveal a weakly alkaline water environment within this glacierized basin, with HCO3- and Ca2+ as the dominant anions and cations, respectively, resulting in a hydrochemical pattern classified as HCO3--Ca2+ type. Solute concentrations increase along the glacier meltwater pathway, influenced by water-rock interaction, dilution, and diverse sources. The cations are predominantly from carbonate weathering, constituting 72.86 % of the total cations, followed by sulfide oxidation (11.08 %), glacier meltwater inputs (8.13 %), and silicate weathering (7.93 %). The contribution of cations from glacier meltwater diminishes as they travel along the glacier meltwater flow pathway. Our study indicates the localized yet significant impact of glacier meltwater on hydrochemistry, particularly in the vicinity of the glacier terminus. We recommend considering glacial meltwater and the entire glacier watershed as a continuum, essential for understanding the cumulative effects of glacier melt and human activities on water quality. This perspective is crucial for predicting future river chemistry trajectories in high-mountain basins and informing policy-making for water quality conservation across the Tibetan Plateau.

The importance of species addition 'versus' replacement varies over succession in plant communities after glacier retreat

The mechanisms underlying plant succession remain highly debated. Due to the local scope of most studies, we lack a global quantification of the relative importance of species addition 'versus' replacement. We assessed the role of these processes in the variation (β-diversity) of plant communities colonizing the forelands of 46 retreating glaciers worldwide, using both environmental DNA and traditional surveys. Our findings indicate that addition and replacement concur in determining community changes in deglaciated sites, but their relative importance varied over time. Taxa addition dominated immediately after glacier retreat, as expected in harsh environments, while replacement became more important for late-successional communities. These changes were aligned with total β-diversity changes, which were more pronounced between early-successional communities than between late-successional communities (>50 yr since glacier retreat). Despite the complexity of community assembly during plant succession, the observed global pattern suggests a generalized shift from the dominance of facilitation and/or stochastic processes in early-successional communities to a predominance of competition later on.

Metagenome-assembled genomes from High Arctic glaciers highlight the vulnerability of glacier-associated microbiota and their activities to habitat loss

The rapid warming of the Arctic is threatening the demise of its glaciers and their associated ecosystems. Therefore, there is an urgent need to explore and understand the diversity of genomes resident within glacial ecosystems endangered by human-induced climate change. In this study we use genome-resolved metagenomics to explore the taxonomic and functional diversity of different habitats within glacier-occupied catchments. Comparing different habitats within such catchments offers a natural experiment for understanding the effects of changing habitat extent or even loss upon Arctic microbiota. Through binning and annotation of metagenome-assembled genomes (MAGs) we describe the spatial differences in taxon distribution and their implications for glacier-associated biogeochemical cycling. Multiple taxa associated with carbon cycling included organisms with the potential for carbon monoxide oxidation. Meanwhile, nitrogen fixation was mediated by a single taxon, although diverse taxa contribute to other nitrogen conversions. Genes for sulphur oxidation were prevalent within MAGs implying the potential capacity for sulphur cycling. Finally, we focused on cyanobacterial MAGs, and those within cryoconite, a biodiverse microbe-mineral granular aggregate responsible for darkening glacier surfaces. Although the metagenome-assembled genome of Phormidesmis priestleyi, the cyanobacterium responsible for forming Arctic cryoconite was represented with high coverage, evidence for the biosynthesis of multiple vitamins and co-factors was absent from its MAG. Our results indicate the potential for cross-feeding to sustain P. priestleyi within granular cryoconite. Taken together, genome-resolved metagenomics reveals the vulnerability of glacier-associated microbiota to the deletion of glacial habitats through the rapid warming of the Arctic.