Differential Colonization and Succession of Microbial Communities in Rock and Soil Substrates on a Maritime Antarctic Glacier Forefield

The effects of climate and soil depth on living and dead bacterial communities along a longitudinal gradient in Chile

Soil bacterial communities play a critical role in shaping soil stability and formation, exhibiting a dynamic interaction with local climate and soil depth. We employed an innovative DNA separation method to characterize microbial assemblages in low-biomass environments such as deserts and distinguish between intracellular DNA (iDNA) and extracellular DNA (eDNA) in soils. This approach, combined with analyses of physicochemical properties and co-occurrence networks, investigated soil bacterial communities across four sites representing diverse climatic gradients (i.e., arid, semi-arid, Mediterranean, and humid) along the Chilean Coastal Cordillera. The separation method yielded a distinctive unimodal pattern in the iDNA pool alpha diversity, increasing from arid to semi-arid climates and decreasing in humid environments, highlighting the rapid feedback of the iDNA community to increasing soil moisture. In the arid region, harsh surface conditions restrict bacterial growth, leading to peak iDNA abundance and diversity occurring in slightly deeper layers than the other sites. Our findings confirmed the association between specialist bacteria and ecosystem-functional traits. We observed transitions from Halomonas and Delftia, resistant to extreme arid environments, to Class AD3 and the genus Bradyrhizobium, associated with plants and organic matter in humid environments. The distance-based redundancy analysis (dbRDA) analysis revealed that soil pH and moisture were the key parameters that influenced bacterial community variation. The eDNA community correlated slightly better with the environment than the iDNA community. Soil depth was found to influence the iDNA community significantly but not the eDNA community, which might be related to depth-related metabolic activity. Our investigation into iDNA communities uncovered deterministic community assembly and distinct co-occurrence modules correlated with unique bacterial taxa, thereby showing connections with sites and key environmental factors. The study additionally revealed the effects of climatic gradients and soil depth on living and dead bacterial communities, emphasizing the need to distinguish between iDNA and eDNA pools.

Biogeography and diversity patterns of abundant and rare bacterial communities in paddy soils along middle and lower Yangtze River

The middle and lower reaches of the Yangtze River serve as principal rice production bases in China, yet the biodiversity and ecological processes of bacterial communities in paddy soils are not well understood. This study explores the diversity, composition, ecological function, and assembly processes of abundant and rare bacterial communities in paddy soils. A total of 129 paddy soil samples from 43 sites along the middle and lower reaches of the Yangtze River were collected and analyzed using NovaSeq sequencing. The results showed that the dominant phylum for both abundant and rare taxa was Proteobacteria, with a greater relative abundance of the abundant taxa. The diversity of the abundant community was lower than that of the rare community. Soil properties and geographic variables explained more of the variation in the abundant community than in the rare community. The rare community exhibited a significant distance-decay relationship. The assembly of the abundant community was more influenced by stochastic processes, although both the abundant and rare communities were governed by stochastic processes. It is concluded that both abundant and rare bacterial communities exhibit differing biogeographic patterns, yet they undergo similar ecological processes in the paddy soils along the middle and lower reaches of the Yangtze River. These observations offer a theoretical framework for a deeper comprehension of the function of both abundant and rare bacteria, as well as the development and preservation of soil bacterial diversity within agricultural ecosystems.

Comparison of Microbial Diversity of Two Typical Volcanic Soils in Wudalianchi, China

Volcanic lava is an excellent model of primary succession, in which basalt-associated microorganisms drive the cycling of different elements such as nitrogen, carbon, and other nutrients. Microbial communities in volcanic soils are of particular interest for study on the emergence and evolution of life within special and extreme conditions. The initial processes of colonization and subsequent rock weathering by microbial communities are still poorly understood. We analyzed the soil bacterial and fungal communities and diversities associated with lava (LBL) and kipuka (BK) sites in Wudalianchi using 16S and ITS rRNA Illumina Miseq sequencing techniques. The results showed that soil physical and chemical properties (pH, MC, TOC, TN, TP, AP, DOC, and DON) significantly differed between LBL and BK. The Shannon, Ace, and Pd indexes of fungi in the two sites showed a significant difference (p < 0.05). The dominant bacterial phyla forming communities at LBL and BK sites were Acidobacteria, Proteobacteria, Actinobacteria, and Basidiomycota, and their differences were driven by Gemmatimonadetes and Verrucomicrobia. The dominant fungal phyla of LBL and BK sites were Ascomycota, Zygomycota, and Rozellomcota, which differed significantly between the two sites. The microbial communities showed extremely significant differences (p < 0.05), with MC, pH, and nitrogen being the main influencing factors according to RDA/CCA and correlation analysis. Microbial functional prediction analysis across the two sites showed that the relative abundance of advantageous functional groups was significantly different (p < 0.05). The combined results drive us to conclude that the volcanic soil differences in the deposits appear to be the main factor shaping the microbial communities in Wudalianchi (WDLC) volcanic ecosystems.

Ornithogenesis and soil-landscape interplays at northern Harmony Point, Nelson Island, Maritime Antarctica

Understanding the influence of soil-forming factors and processes in ornithogenic soils is important to predict impacts of climate change on Antarctic ecosystems. Herein, we analyzed the soil-landscape interplays and development of ornithogenic soils at Harmony Point (HP), Nelson Island. We collected, described, and classified 24 soil profiles, combined with vegetation and landforms descriptions. Geoprocessing techniques were employed for mapping. Soil physical, chemical, geochemical, and mineralogical analyses were applied. Patterned ground, "Ornithogenic"/Typic Gelorthent, and moss carpets were the dominant landform, soil and vegetation classes, respectively. Soils from rocky outcrops were more structured, acidic, with higher organic carbon, organometallic complexes, and secondary phosphate minerals, due to former bird influence. Soils from cryoplanated platforms presented higher water pH, base saturation, clay content, and secondary silicate minerals. Soils from marine terraces presented high exchangeable bases, phosphorous, and amorphous phosphate minerals. Soil chemical weathering is enhanced by ornithogenesis and widespread in HP. Besides ornithogenesis, organic matter accumulation, cryoturbation, and cryoclastic processes are also important to pedogenesis of ornithogenic soils. The soils of the cryoplanated platforms exhibited a gradient of pedogenetic development corresponding to increasing biota influence and distance from glacier. In contrast, soils of rocky outcrops were more developed even close to the glacier, due to ornithogenesis.

Wide divergence of fungal communities inhabiting rocks and soils in a hyper-arid Antarctic desert

Highly simplified microbial communities colonise rocks and soils of continental Antarctica ice-free deserts. These two habitats impose different selection pressures on organisms, yet the possible filtering effects on the diversity and composition of microbial communities have not hitherto been fully characterised. We hence compared fungal communities in rocks and soils in three localities of inner Victoria Land. We found low fungal diversity in both substrates, with a mean species richness of 28 across all samples, and significantly lower diversity in rocks than in soils. Rock and soil communities were strongly differentiated, with a multinomial species classification method identifying just three out of 328 taxa as generalists with no affinity for either substrate. Rocks were characterised by a higher abundance of lichen-forming fungi (typically Buellia, Carbonea, Pleopsidium, Lecanora, and Lecidea), possibly owing to the more protected environment and the porosity of rocks permitting photosynthetic activity. In contrast, soils were dominated by obligate yeasts (typically Naganishia and Meyerozyma), the abundances of which were correlated with edaphic factors, and the black yeast Cryomyces. Our study suggests that strong differences in selection pressures may account for the wide divergences of fungal communities in rocks and soils of inner Victoria Land.

Microbial dynamics in soils of the Damma glacier forefield show succession in the functional genetic potential

Glacier retreat is a visible consequence of climate change worldwide. Although taxonomic change of the soil microbiomes in glacier forefields have been widely documented, how microbial genetic potential changes along succession is little known. Here, we used shotgun metagenomics to analyse whether the soil microbial genetic potential differed between four stages of soil development (SSD) sampled along three transects in the Damma glacier forefield (Switzerland). The SSDs were characterized by an increasing vegetation cover, from barren soil, to biological soil crust, to sparsely vegetated soil and finally to vegetated soil. Results suggested that SSD significantly influenced microbial genetic potential, with the lowest functional diversity surprisingly occurring in the vegetated soils. Overall, carbohydrate metabolism and secondary metabolite biosynthesis genes overrepresented in vegetated soils, which could be partly attributed to plant-soil feedbacks. For C degradation, glycoside hydrolase genes enriched in vegetated soils, while auxiliary activity and carbohydrate esterases genes overrepresented in barren soils, suggested high labile C degradation potential in vegetated, and high recalcitrant C degradation potential in barren soils. For N-cycling, organic N degradation and synthesis genes dominated along succession, and gene families involved in nitrification were overrepresented in barren soils. Our study provides new insights into how the microbial genetic potential changes during soil formation along the Damma glacier forefield.

The hind information: Exploring the impact of physical damage on mask microbial composition in the aquatic environment

Due to poor management and the lack of environmental awareness, lots of masks (an emerging form of plastic pollution) are discarded into the environment during the COVID-19, thereby jeopardizing the health of humans and the environment. Our study introduces a novel perspective by examining the impact of physical damage on the microbial composition of masks in the water environment. We focus on the variations in biofilm formation on each layer of both damaged and undamaged masks, which allows us to understand more about the biofilm on each layer and the significant changes that occur when masks are physically damaged. Research has shown that the community structure of microorganisms on discarded masks can be altered in just ten days, showing an evolution from undifferentiated pioneer colonizing species ("non-picky") to adaptive dominant species ("picky"). Especially, considering that discarded masks were inevitably damaged, we found that the biomass on the damaged samples is 1.62-2.38 times higher than that of the undamaged samples, respectively. Moreover, the microbial community structure on it was also significantly different. Genes involved in biogeochemical cycles of nutrients are more enriched in damaged masks. When damaged, the colonization process and community structure in the middle layer significantly differ from those in the inner and outer layers and even enrich more pathogenic bacteria. Based on the above, it is evident that the environmental risk of masks cannot be assessed as a whole, and the middle layer carries a higher risk.

Innovative approaches to accurately assess the effectiveness of biocide-based treatments to fight biodeterioration of Cultural Heritage monuments

The development of diagnostic methods to accurately assess the effects of treatments on lithobiont colonization remains a challenge for the conservation of Cultural Heritage monuments. In this study, we tested the efficacy of biocide-based treatments on microbial colonization of a dolostone quarry, in the short and long-term, using a dual analytical strategy. We applied a metabarcoding approach to characterize fungal and bacterial communities over time, integrated with microscopy techniques to analyze the interactions of microorganisms with the substrate and evaluate the effectiveness. These communities were dominated by the bacterial phyla Actinobacteriota, Proteobacteria and Cyanobacteria, and the fungal order Verrucariales, which include taxa previously reported as biodeteriogenic agents and observed here associated with biodeterioration processes. Following the treatments, changes over time in the abundance profiles depend on taxa. While Cyanobacteriales, Cytophagales and Verrucariales decreased in abundance, other groups, such as Solirubrobacteriales, Thermomicrobiales and Pleosporales increased. These patterns could be related not only to the specific effects of the biocide on the different taxa, but also to different recolonization abilities of those organisms. The different susceptibility to treatments could be associated with the inherent cellular properties of different taxa, but differences in biocide penetration to endolithic microhabitats could be involved. Our results demonstrate the importance of both removing epilithic colonization and applying biocides to act against endolithic forms. Recolonization processes could also explain some of the taxon-dependent responses, especially in the long-term. Taxa showing resistance, and those benefiting from nutrient accumulation in the form of cellular debris following treatments, may have an advantage in colonizing treated areas, pointing to the need for long-term monitoring of a wide range of taxa. This study highlights the potential utility of combining metabarcoding and microscopy to analyze the effects of treatments and design appropriate strategies to combat biodeterioration and establish preventive conservation protocols.

The role of subsurface ice in sustaining bacteria in continental and maritime glaciers

In supraglacial environments, surface and subsurface ices are two distinct and connected microhabitats in terms of physicochemical and biological aspects. At the frontline of climate change, glaciers lose tremendous ice masses to downstream ecosystems, serving as crucial sources of both biotic and abiotic materials. In this study, we studied the disparities and relationships of microbial communities between surface and subsurface ices collected from a maritime and a continental glacier during summer. The results showed that surface ices had significantly higher nutrients and were more physiochemically different than subsurface ices. Despite lower nutrients, subsurface ices had higher alpha-diversity with more unique and enriched operational taxonomic units (OTUs) than surface ices, indicating the potential role of subsurface as a bacterial refuge. Sorensen dissimilarity between bacterial communities in surface ices and subsurface ices was mainly contributed by the turnover component, suggesting strong species replacement from surface to subsurface ices due to large environmental gradients. For different glaciers, the maritime glacier had significantly higher alpha-diversity than the continental glacier. The difference between surface and subsurface communities was more pronounced in the maritime glacier than in the continental glacier. The network analysis revealed that surface-enriched and subsurface-enriched OTUs formed independent modules, with surface-enriched OTUs having closer interconnections and greater importance in the network of the maritime glacier. This study highlights the important role of subsurface ice as a bacterial refuge and enriches our knowledge of microbial properties in glaciers.

Moss and Liverwort Covers Structure Soil Bacterial and Fungal Communities Differently in the Icelandic Highlands

Cryptogamic covers extend over vast polar tundra regions and their main components, e.g., bryophytes and lichens, are frequently the first visible colonizers of deglaciated areas. To understand their role in polar soil development, we analyzed how cryptogamic covers dominated by different bryophyte lineages (mosses and liverworts) influence the diversity and composition of edaphic bacterial and fungal communities as well as the abiotic attributes of underlying soils in the southern part of the Highlands of Iceland. For comparison, the same traits were examined in soils devoid of bryophyte covers. We measured an increase in soil C, N, and organic matter contents coupled with a lower pH in association with bryophyte cover establishment. However, liverwort covers showed noticeably higher C and N contents than moss covers. Significant changes in diversity and composition of bacterial and fungal communities were revealed between (a) bare and bryophyte-covered soils, (b) bryophyte covers and the underlying soils, and (c) moss and liverworts covers. These differences were more obvious for fungi than bacteria, and involved different lineages of saprotrophic and symbiotic fungi, which suggests a certain specificity of microbial taxa to particular bryophyte groups. In addition, differences observed in the spatial structure of the two bryophyte covers may be also responsible for the detected differences in microbial community diversity and composition. Altogether, our findings indicate that soil microbial communities and abiotic attributes are ultimately affected by the composition of the most conspicuous elements of cryptogamic covers in polar regions, which is of great value to predict the biotic responses of these ecosystems to future climate change.

Mineral substrate quality determines the initial soil microbial development in front of the Nordenskiöldbreen, Svalbard

Substrate geochemistry is an important factor influencing early microbial development after glacial retreat on nutrient-poor geological substrates in the High Arctic. It is often difficult to separate substrate influence from climate because study locations are distant. Our study in the retreating Nordenskiöldbreen (Svalbard) is one of the few to investigate biogeochemical and microbial succession in two adjacent forefields, which share the same climatic conditions but differ in their underlying geology. The northern silicate forefield evolved in a classical chronosequence, where most geochemical and microbial parameters increased gradually with time. In contrast, the southern carbonate forefield exhibited high levels of nutrients and microbial biomass at the youngest sites, followed by a significant decline and then a gradual increase, which caused a rearrangement in the species and functional composition of the bacterial and fungal communities. This shuffling in the early stages of succession suggests that high nutrient availability in the bedrock could have accelerated early soil succession after deglaciation and thereby promoted more rapid stabilization of the soil and production of higher quality organic matter. Most chemical parameters and bacterial taxa converged with time, while fungi showed no clear pattern.

Synergistic effects of succession and microtopography of moraine on the fungal spatial diversity in a glacier forefield

Primary succession and microtopography result in environmental changes and are important processes influencing the community assembly of soil fungi in the Arctic region. In glacier forefields that contain a series of moraine ridges, both processes contribute synchronously to fungal spatial diversity. To reveal the synergistic effects of succession and microtopography, we investigated the fungal community structure and environmental variables in the moraines of the Arklio Glacier, Ellesmere Island. The study sites were established at four locations from the top to the bottom of the ridge slope within each of the three moraine ridges of different post-glacial ages. The location-dependent community composition was equally diverse in both the initial and later stages of succession, suggesting that successional time could alter the effects of microtopography on the fungal community. Moreover, our results suggest that fungal communities at different locations follow different successional trajectories, even if they have passed through the same time lapse. Such a synergistic effect of succession and microtopography of moraines does not allow for parallel changes in fungal communities among moraines or among locations, suggesting that the moraine series contributes substantially to fungal spatial diversity in the glacier forefield.

Unrecognized diversity and distribution of soil algae from Maritime Antarctica (Fildes Peninsula, King George Island)

Introduction

Eukaryotic algae in the top few centimeters of fellfield soils of ice-free Maritime Antarctica have many important effects on their habitat, such as being significant drivers of organic matter input into the soils and reducing the impact of wind erosion by soil aggregate formation. To better understand the diversity and distribution of Antarctic terrestrial algae, we performed a pilot study on the surface soils of Meseta, an ice-free plateau mountain crest of Fildes Peninsula, King George Island, being hardly influenced by the marine realm and anthropogenic disturbances. It is openly exposed to microbial colonization from outside Antarctica and connected to the much harsher and dryer ice-free zones of the continental Antarctic. A temperate reference site under mild land use, SchF, was included to further test for the Meseta algae distribution in a contrasting environment.

Methods

We employed a paired-end metabarcoding analysis based on amplicons of the highly variable nuclear-encoded ITS2 rDNA region, complemented by a clone library approach. It targeted the four algal classes, Chlorophyceae, Trebouxiophyceae, Ulvophyceae, and Xanthophyceae, representing key groups of cold-adapted soil algae.

Results

A surprisingly high diversity of 830 algal OTUs was revealed, assigned to 58 genera in the four targeted algal classes. Members of the green algal class Trebouxiophyceae predominated in the soil algae communities. The major part of the algal biodiversity, 86.1% of all algal OTUs, could not be identified at the species level due to insufficient representation in reference sequence databases. The classes Ulvophyceae and Xanthophyceae exhibited the most unknown species diversity. About 9% of the Meseta algae species diversity was shared with that of the temperate reference site in Germany.

Discussion

In the small portion of algal OTUs for which their distribution could be assessed, the entire ITS2 sequence identity with references shows that the soil algae likely have a wide distribution beyond the Polar regions. They probably originated from soil algae propagule banks in far southern regions, transported by aeolian transport over long distances. The dynamics and severity of environmental conditions at the soil surface, determined by high wind currents, and the soil algae's high adaptability to harsh environmental conditions may account for the high similarity of soil algal communities between the northern and southern parts of the Meseta.

Trajectories of freshwater microbial genomics and greenhouse gas saturation upon glacial retreat

Due to climate warming, ice sheets around the world are losing mass, contributing to changes across terrestrial landscapes on decadal time spans. However, landscape repercussions on climate are poorly constrained mostly due to limited knowledge on microbial responses to deglaciation. Here, we reveal the genomic succession from chemolithotrophy to photo- and heterotrophy and increases in methane supersaturation in freshwater lakes upon glacial retreat. Arctic lakes at Svalbard also revealed strong microbial signatures form nutrient fertilization by birds. Although methanotrophs were present and increased along lake chronosequences, methane consumption rates were low even in supersaturated systems. Nitrous oxide oversaturation and genomic information suggest active nitrogen cycling across the entire deglaciated landscape, and in the high Arctic, increasing bird populations serve as major modulators at many sites. Our findings show diverse microbial succession patterns, and trajectories in carbon and nitrogen cycle processes representing a positive feedback loop of deglaciation on climate warming.

Environmental micro-niche filtering shapes bacterial pioneer communities during primary colonization of a Himalayas' glacier forefield

The pedogenesis from the mineral substrate released upon glacier melting has been explained with the succession of consortia of pioneer microorganisms, whose structure and functionality are determined by the environmental conditions developing in the moraine. However, the microbiome variability that can be expected in the environmentally heterogeneous niches occurring in a moraine at a given successional stage is poorly investigated. In a 50 m² area in the forefield of the Lobuche glacier (Himalayas, 5050 m above sea level), we studied six sites of primary colonization presenting different topographical features (orientation, elevation and slope) and harbouring greyish/dark biological soil crusts (BSCs). The spatial vicinity of the sites opposed to their topographical differences, allowed us to examine the effect of environmental conditions independently from the time of deglaciation. The bacterial microbiome diversity and their co-occurrence network, the bacterial metabolisms predicted from 16S rRNA gene high-throughput sequencing, and the microbiome intact polar lipids were investigated in the BSCs and the underlying sediment deep layers (DLs). Different bacterial microbiomes inhabited the BSCs and the DLs, and their composition varied among sites, indicating a niche-specific role of the micro-environmental conditions in the bacterial communities' assembly. In the heterogeneous sediments of glacier moraines, physico-chemical and micro-climatic variations at the site-spatial scale are crucial in shaping the microbiome microvariability and structuring the pioneer bacterial communities during pedogenesis.

Community assembly in the wake of glacial retreat: A meta-analysis

Ecosystems shaped by retreating glaciers provide a unique opportunity to study the order and timing of biotic colonization, and how this influences the structure of successive ecological communities. In the last century glaciers across most of the cryosphere have receded at an unprecedented pace. Many studies have been published from different parts of the world testing hypotheses about how soil ecosystems are responding to rapid, contemporary deglaciation events. To better understand and draw general conclusions about how soil ecosystems respond to deglaciation, we conducted a global meta-analysis of 95 published articles focused on the succession of various organisms and soil physicochemical properties in glacier forefields along the chronosequence. Our global synthesis reveals that key soil properties and the abundance and richness of biota follow two conspicuous patterns: (1) some taxa demonstrate a persistent increase in abundance and richness over the entire chronosequence, (2) other taxa increase in abundance and richness during the first 50 years of succession, then gradually decline 50 years onward. The soil properties and soil organisms that are intimately tied to vegetation follow the first pattern, consistent with the idea that aboveground patterns of vegetation can drive patterns of belowground biodiversity. The second pattern may be due to an initial increase and subsequent decline in available nutrients and habitat suitability caused by increased biotic interactions, including resource competition among soil biota. A consensus view of the patterns of historical and contemporary soil ecosystem responses to deglaciation provides a better understanding of the processes that generate these patterns and informs predictions of ongoing and future responses to environmental changes.

Dynamic trophic shifts in bacterial and eukaryotic communities during the first 30 years of microbial succession following retreat of an Antarctic glacier

We examined microbial succession along a glacier forefront in the Antarctic Peninsula representing ∼30 years of deglaciation to contrast bacterial and eukaryotic successional dynamics and abiotic drivers of community assembly using sequencing and soil properties. Microbial communities changed most rapidly early along the chronosequence, and co-occurrence network analysis showed the most complex topology at the earliest stage. Initial microbial communities were dominated by microorganisms derived from the glacial environment, whereas later stages hosted a mixed community of taxa associated with soils. Eukaryotes became increasingly dominated by Cercozoa, particularly Vampyrellidae, indicating a previously unappreciated role for cercozoan predators during early stages of primary succession. Chlorophytes and Charophytes (rather than cyanobacteria) were the dominant primary producers and there was a spatio-temporal sequence in which major groups became abundant succeeding from simple ice Chlorophytes to Ochrophytes and Bryophytes. Time since deglaciation and pH were the main abiotic drivers structuring both bacterial and eukaryotic communities. Determinism was the dominant assembly mechanism for Bacteria, while the balance between stochastic/deterministic processes in eukaryotes varied along the distance from the glacier front. This study provides new insights into the unexpected dynamic changes and interactions across multiple trophic groups during primary succession in a rapidly changing polar ecosystem.

Vegetation drives the response of the active fraction of the rhizosphere microbial communities to soil warming in Antarctic vascular plants

In the Antarctic Peninsula, increases in mean annual temperature are associated with the coverage and population density of the two Antarctic vascular plant species-Deschampsia antarctica and Colobanthus quitensis-potentially modifying critical soil processes. In this study, we characterized the diversity and community composition of active microorganisms inhabiting the vascular plant rhizosphere in two sites with contrasting vegetation cover in King George Island, Western Antarctic Peninsula. We assessed the interplay between soil physicochemical properties and microbial diversity and composition, evaluating the effect of an in situ experimental warming on the microbial communities of the rhizosphere from D. antarctica and C. quitensis. Bacteria and Eukarya showed different responses to warming in both sites, and the effect was more noticeable in microbial eukaryotes from the low vegetation site. Furthermore, important changes were found in the relative abundance of Tepidisphaerales (Bacteria) and Ciliophora (Eukarya) between warming and control treatments. Our results showed that rhizosphere eukaryal communities are more sensitive to in situ warming than bacterial communities. Overall, our results indicate that vegetation drives the response of the active fraction of the microbial communities from the rhizosphere of Antarctic vascular plants to soil warming.

Microbial Community Structure and Metabolic Potential at the Initial Stage of Soil Development of the Glacial Forefields in Svalbard

Microbial communities have been identified as the primary inhabitants of Arctic forefields. However, the metabolic potential of microbial communities in these newly exposed soils remains underexplored due to limited access. Here, we sampled the very edge of the glacial forefield in Svalbard and performed the 16S rRNA genes and metagenomic analysis to illustrate the ecosystem characteristics. Burkholderiales and Micrococcales were the dominant bacterial groups at the initial stage of soil development of glacial forefields. 214 metagenome-assembled genomes were recovered from glacier forefield microbiome datasets, including only 2 belonging to archaea. Analysis of these metagenome-assembled genomes revealed that 41% of assembled genomes had the genetic potential to use nitrate and nitrite as electron acceptors. Metabolic pathway reconstruction for these microbes suggested versatility for sulfide and thiosulfate oxidation, H₂ and CO utilization, and CO₂ fixation. Our results indicate the importance of anaerobic processes in elemental cycling in the glacial forefields. Besides, a range of genes related to adaption to low temperature and other stresses were detected, which revealed the presence of diverse mechanisms of adaption to the extreme environment of Svalbard. This research provides ecological insight into the initial stage of the soil developed during the retreating of glaciers.

Islands in the ice: Potential impacts of habitat transformation on Antarctic biodiversity

Antarctic biodiversity faces an unknown future with a changing climate. Most terrestrial biota is restricted to limited patches of ice-free land in a sea of ice, where they are adapted to the continent's extreme cold and wind and exploit microhabitats of suitable conditions. As temperatures rise, ice-free areas are predicted to expand, more rapidly in some areas than others. There is high uncertainty as to how species' distributions, physiology, abundance, and survivorship will be affected as their habitats transform. Here we use current knowledge to propose hypotheses that ice-free area expansion (i) will increase habitat availability, though the quality of habitat will vary; (ii) will increase structural connectivity, although not necessarily increase opportunities for species establishment; (iii) combined with milder climates will increase likelihood of non-native species establishment, but may also lengthen activity windows for all species; and (iv) will benefit some species and not others, possibly resulting in increased homogeneity of biodiversity. We anticipate considerable spatial, temporal, and taxonomic variation in species responses, and a heightened need for interdisciplinary research to understand the factors associated with ecosystem resilience under future scenarios. Such research will help identify at-risk species or vulnerable localities and is crucial for informing environmental management and policymaking into the future.

Source and acquisition of rhizosphere microbes in Antarctic vascular plants

Rhizosphere microbial communities exert critical roles in plant health, nutrient cycling, and soil fertility. Despite the essential functions conferred by microbes, the source and acquisition of the rhizosphere are not entirely clear. Therefore, we investigated microbial community diversity and potential source using the only two native Antarctic plants, Deschampsia antarctica (Da) and Colobanthus quitensis (Cq), as models. We interrogated rhizosphere and bulk soil microbiomes at six locations in the Byers Peninsula, Livingston Island, Antarctica, both individual plant species and their association (Da.Cq). Our results show that host plant species influenced the richness and diversity of bacterial communities in the rhizosphere. Here, the Da rhizosphere showed the lowest richness and diversity of bacteria compared to Cq and Da.Cq rhizospheres. In contrast, for rhizosphere fungal communities, plant species only influenced diversity, whereas the rhizosphere of Da exhibited higher fungal diversity than the Cq rhizosphere. Also, we found that environmental geographic pressures (i.e., sampling site, latitude, and altitude) and, to a lesser extent, biotic factors (i.e., plant species) determined the species turnover between microbial communities. Moreover, our analysis shows that the sources of the bacterial communities in the rhizosphere were local soils that contributed to homogenizing the community composition of the different plant species growing in the same sampling site. In contrast, the sources of rhizosphere fungi were local (for Da and Da.Cq) and distant soils (for Cq). Here, the host plant species have a specific effect in acquiring fungal communities to the rhizosphere. However, the contribution of unknown sources to the fungal rhizosphere (especially in Da and Da.Cq) indicates the existence of relevant stochastic processes in acquiring these microbes. Our study shows that rhizosphere microbial communities differ in their composition and diversity. These differences are explained mainly by the microbial composition of the soils that harbor them, acting together with plant species-specific effects. Both plant species acquire bacteria from local soils to form part of their rhizosphere. Seemingly, the acquisition process is more complex for fungi. We identified a significant contribution from unknown fungal sources due to stochastic processes and known sources from soils across the Byers Peninsula.

Rare bacterial biosphere is more environmental controlled and deterministically governed than abundant one in sediment of thermokarst lakes across the Qinghai-Tibet Plateau

Thermokarst lakes are widely distributed in cold regions as a result of ice-rich permafrost thaw. Disentangling the biogeography of abundant and rare microbes is essential to understanding the environmental influences, assembly mechanisms, and responses to climate change of bacterial communities in thermokarst lakes. In light of this, we assessed the abundant and rare bacterial subcommunities in sediments from thermokarst lakes across the Qinghai-Tibet Plateau (QTP). The operational taxonomic unit (OTU) richness was more strongly associated with location and climate factors for abundant subcommunities, while more strongly associated with physicochemical variables for rare subcommunities. The relative abundance of abundant and rare taxa showed opposite patterns with abundant taxa having greater relative abundance at higher latitude and pH, but at lower mean annual precipitation and nutrients. Both the abundant and rare subcommunities had a clear distribution pattern along the gradient of latitude and mean annual precipitation. Abundant subcommunities were dominantly shaped by dispersal limitation processes (80.9%), while rare subcommunities were shaped almost equally by deterministic (47.3%) and stochastic (52.7%) processes. The balance between stochastic and deterministic processes was strongly environmentally adjusted for rare subcommunities, while not associated with environmental changes for abundant subcommunities. The results shed light on biogeography patterns and structuring mechanisms of bacterial communities in thermokarst lakes, improving our ability to predict the influences of future climate change on these lakes.

Abundant and rare soil fungi exhibit distinct succession patterns in the forefield of Dongkemadi glacier on the central Qinghai-Tibet Plateau

Glaciers are retreating rapidly, exposing extensive new soil habitats in glacier forefields and providing unique areas for studying primary succession. However, understanding the variation patterns and assembly mechanisms of abundant and rare fungi subcommunities along the glacier-retreating chronosequence remains a knowledge gap, especially true for the vast Qinghai-Tibet Plateau (QTP). Here, we investigated fungal communities in the glacier forefield in Dongkemadi Glaicer on the central QTP. The results showed that fungal alpha diversity exhibited a clear increasing pattern in response to increasing of distance to glacier. The percentage of abundant OTUs decreased while the percentage of rare OTUs increased, suggesting that soil development is more beneficial to the rare taxa. The distributions of both abundant and rare subcommunities exhibited a clear spatial pattern along the distance to glacier, and might be strongly controlled by multiple environmental variables, including pH, soil moisture, vegetation status, soil organic carbon, total nitrogen, and soluble reactive phosphorus. Abundant and rare fungal subcommunities were structured in different assembly regimes. Dispersal limitation processes were dominant for both abundant and rare subcommunities but with a stronger contribution to abundant subcommunity assembly. Heterogeneous selection processes contributed higher and non-dominant processes contributed lower to abundant subcommunities than to rare subcommunities. The modular structure of the fungal co-occurrence network was highly localized along the soil chronosequence. By revealing distinct diversity patterns and community assembly mechanisms of abundant and rare fungal subcommunities, our study improved our understanding of ecological succession along the glacier-retreating chronosequence.

Impact of Climate and Slope Aspects on the Composition of Soil Bacterial Communities Involved in Pedogenetic Processes along the Chilean Coastal Cordillera

Soil bacteria play a fundamental role in pedogenesis. However, knowledge about both the impact of climate and slope aspects on microbial communities and the consequences of these items in pedogenesis is lacking. Therefore, soil-bacterial communities from four sites and two different aspects along the climate gradient of the Chilean Coastal Cordillera were investigated. Using a combination of microbiological and physicochemical methods, soils that developed in arid, semi-arid, mediterranean, and humid climates were analyzed. Proteobacteria, Acidobacteria, Chloroflexi, Verrucomicrobia, and Planctomycetes were found to increase in abundance from arid to humid climates, while Actinobacteria and Gemmatimonadetes decreased along the transect. Bacterial-community structure varied with climate and aspect and was influenced by pH, bulk density, plant-available phosphorus, clay, and total organic-matter content. Higher bacterial specialization was found in arid and humid climates and on the south-facing slope and was likely promoted by stable microclimatic conditions. The presence of specialists was associated with ecosystem-functional traits, which shifted from pioneers that accumulated organic matter in arid climates to organic decomposers in humid climates. These findings provide new perspectives on how climate and slope aspects influence the composition and functional capabilities of bacteria, with most of these capabilities being involved in pedogenetic processes.

Rocks support a distinctive and consistent mycobiome across contrasting dry regions of Earth

Rock-dwelling fungi play critical ecological roles in drylands, including soil formation and nutrient cycling; however, we know very little about the identity, function and environmental preferences of these important organisms, and the mere existence of a consistent rock mycobiome across diverse arid regions of the planet remains undetermined. To address this knowledge gap, we conducted a meta-analysis of rock fungi and spatially associated soil communities, surveyed across 28 unique sites spanning four major biogeographic regions (North America, Arctic, Maritime and Continental Antarctica) including contrasting climates, from cold and hot deserts to semi-arid drylands. We show that rocks support a consistent and unique mycobiome that was different to that found in surrounding soils. Lichenized fungi from class Lecanoromycetes were consistently indicative of rocks across contrasting regions, together with ascomycetous representatives of black fungi in Arthoniomycetes, Dothideomycetes, and Eurotiomycetes. In addition, comparing to soil, rocks had a lower proportion of saprobes and plant symbiotic fungi. The main drivers structuring rock fungi distribution were spatial distance and, to a larger extent, climatic factors regulating moisture and temperature (i.e. mean annual temperature and mean annual precipitation), suggesting that these paramount and unique communities might be particularly sensitive to increases in temperature and desertification.

Using metabarcoding to assess Viridiplantae sequence diversity present in Antarctic glacial ice

Antarctica contains most of the glacial ice on the planet, a habitat that is largely unexplored by biologists. Recent warming in parts of Antarctica, particularly the Antarctic Peninsula region, is leading to widespread glacial retreat, releasing melt water and, potentially, contained biological material and propagules. In this study, we used a DNA metabarcoding approach to characterize Viridiplantae DNA present in Antarctic glacial ice. Ice samples from six glaciers in the South Shetland Islands and Antarctic Peninsula were analysed, detecting the presence of DNA representing a total of 16 taxa including 11 Chlorophyta (green algae) and five Magnoliophyta (flowering plants). The green algae may indicate the presence of a viable algal community in the ice or simply of preserved DNA, and the sequence diversity assigned included representatives of Chlorophyta not previously recorded in Antarctica. The presence of flowering plant DNA is most likely to be associated with pollen or tissue fragments introduced by humans.

Diazotrophic activity and denitrification in two long-term chronosequences of maritime Antarctica

The main goals of this study were to identify whether key processes involved in microbial soil nitrogen transformations, such as diazotrophic activity and denitrification, the chemical properties of limiting elements in the soil, and microbial community structure, differ in the different successional stages of two long term chronosequences in maritime Antarctica. Moreover, we expect the rates of diazotrophic activity and denitrification to be stimulated by increases in air temperature and moisture. To answer these questions, we selected three stages in the succession (early, mid and late) in each of two well established chronosequences: three raised beaches in Ardley Island; and the Barton Peninsula, which includes two cosmogenically dated sites and the forefield of the Fourcade glacier. In the Ardley chronosequence, higher diazotrophic activity was found in the older successional stages, concomitant with an increase in the abundance of Cyanobacteria. In the Barton chronosequence, Cyanobacteria were only present and abundant (Microcoleus) in the early successional stage, coinciding with the highest diazotrophic activity. Denitrification in the Barton chronosequence tended to be highest at the mid successional sites, associated with the highest abundance of Rhodanobacter. In the Ardley chronosequence, the lowest abundance of Rhodanobacter was linked to lower denitrification rates in the mid successional stage. In the Ardley chronosequence, significant positive effects of passive warming and water addition on diazotrophic activity were detected in the first and the second years of the study respectively. In the Barton chronosequence on the other hand, there was no response to either passive warming or water addition, probably a manifestation of the higher nutrient limitation in this site. Denitrification showed no response to either warming or water addition. Thus, the response of microbial nitrogen transformations to global change is highly dependent on the environmental setting, such as soil origin, age and climate regime.

Are microorganisms everywhere they can be?

Baas-Becking is famously attributed with the conjecture that 'everything is everywhere, but the environment selects'. Although this aphorism is largely challenged by microbial biogeographical data, even weak versions of the claim leave unanswered the question about whether all environments that could theoretically support life contain life. In the last decade, the discovery of thermally sterilized habitable environments disconnected from inhabited regions, and habitats within organisms such as the sterile, but habitable human fetal gut, suggest the existence of a diversity of macroscopic habitable environments apparently devoid of actively metabolizing or reproducing life. Less clear is the status of such environments at the micron scale, for example, between colonies of organisms within rock interstices or on and within other substrates. I discuss recent evidence for these types of environments. These environments have practical uses in: (i) being negative controls for understanding the role of microbial processes in geochemical cycles and geological processes, (ii) yielding insights into the extent to which the biosphere extends into all spaces it theoretically can, (iii) suggesting caution in interpreting the results of life detection instrumentation, and (iv) being useful for establishing the conditions for the origin of life and its prevalence on other planetary bodies.

Green algae (Viridiplantae) in sediments from three lakes on Vega Island, Antarctica, assessed using DNA metabarcoding

BACKGROUND

Vega Island is located off the eastern tip of the Antarctic Peninsula (Maritime Antarctica), in the Weddell Sea. In this study, we used metabarcoding to investigate green algal DNA sequence diversity present in sediments from three lakes on Vega Island (Esmeralda, Copépodo, and Pan Negro Lakes).

METHODS AND RESULTS

Total DNA was extracted and the internal transcribed spacer 2 region of the nuclear ribosomal DNA was used as a DNA barcode for molecular identification. Green algae were represented by sequences representing 78 taxa belonging to Phylum Chlorophyta, of which 32% have not previously been recorded from Antarctica. Sediment from Pan Negro Lake generated the highest number of DNA reads (11,205), followed by Esmeralda (9085) and Copépodo (1595) Lakes. Esmeralda Lake was the richest in terms of number of taxa (59), with Copépodo and Pan Negro Lakes having 30 taxa each. Bray-Curtis dissimilarity among lakes was high (~ 0.80). The Order Chlamydomonadales (Chlorophyceae) gave the highest contribution in terms of numbers of taxa and DNA reads in all lakes. The most abundant taxon was Chlorococcum microstigmatum.

CONCLUSIONS

The study confirms the utility of DNA metabarcoding in assessing potential green algal diversity in Antarctic lakes, generating new Antarctic records.

Geomicrobiological Heterogeneity of Lithic Habitats in the Extreme Environment of Antarctic Nunataks: A Potential Early Mars Analog

Nunataks are permanent ice-free rocky peaks that project above ice caps in polar regions, thus being exposed to extreme climatic conditions throughout the year. They undergo extremely low temperatures and scarcity of liquid water in winter, while receiving high incident and reflected (albedo) UVA-B radiation in summer. Here, we investigate the geomicrobiology of the permanently exposed lithic substrates of nunataks from Livingston Island (South Shetlands, Antarctic Peninsula), with focus on prokaryotic community structure and their main metabolic traits. Contrarily to first hypothesis, an extensive sampling based on different gradients and multianalytical approaches demonstrated significant differences for most geomicrobiological parameters between the bedrock, soil, and loose rock substrates, which overlapped any other regional variation. Brevibacillus genus dominated on bedrock and soil substrates, while loose rocks contained a diverse microbial community, including Actinobacteria, Alphaproteobacteria and abundant Cyanobacteria inhabiting the milder and diverse microhabitats within. Archaea, a domain never described before in similar Antarctic environments, were also consistently found in the three substrates, but being more abundant and potentially more active in soils. Stable isotopic ratios of total carbon (δ ¹³C) and nitrogen (δ ¹⁵N), soluble anions concentrations, and the detection of proteins involved in key metabolisms via the Life Detector Chip (LDChip), suggest that microbial primary production has a pivotal role in nutrient cycling at these exposed areas with limited deposition of nutrients. Detection of stress-resistance proteins, such as molecular chaperons, suggests microbial molecular adaptation mechanisms to cope with these harsh conditions. Since early Mars may have encompassed analogous environmental conditions as the ones found in these Antarctic nunataks, our study also contributes to the understanding of the metabolic features and biomarker profiles of a potential Martian microbiota, as well as the use of LDChip in future life detection missions.

Contrasting early successional dynamics of bacterial and fungal communities in recently deglaciated soils of the maritime Antarctic

Although microorganisms are the very first colonizers of recently deglaciated soils even prior to plant colonization, the drivers and patterns of microbial community succession at early-successional stages remain poorly understood. The successional dynamics and assembly processes of bacterial and fungal communities were compared on a glacier foreland in the maritime Antarctic across the ~10-year soil-age gradient from bare soil to sparsely vegetated area. Bacterial communities shifted more rapidly than fungal communities in response to glacial retreat; species turnover (primarily the transition from glacier- to soil-favouring taxa) contributed greatly to bacterial beta diversity, but this pattern was less clear in fungi. Bacterial communities underwent more predictable (more deterministic) changes along the soil-age gradient, with compositional changes paralleling the direction of changes in soil physicochemical properties following deglaciation. In contrast, the compositional shift in fungal communities was less associated with changes in deglaciation-induced changes in soil geochemistry and most fungal taxa displayed mosaic abundance distribution across the landscape, suggesting that the successional dynamics of fungal communities are largely governed by stochastic processes. A co-occurrence network analysis revealed that biotic interactions between bacteria and fungi are very weak in early succession. Taken together, these results collectively suggest that bacterial and fungal communities in recently deglaciated soils are largely decoupled from each other during succession and exert very divergent trajectories of succession and assembly under different selective forces.

Influence of prokaryotic microorganisms on initial soil formation along a glacier forefield on King George Island, maritime Antarctica

Compared to the 1970s, the edge of the Ecology Glacier on King George Island, maritime Antarctica, is positioned more than 500 m inwards, exposing a large area of new terrain to soil-forming processes and periglacial climate for more than 40 years. To gain information on the state of soil formation and its interplay with microbial activity, three hyperskeletic Cryosols (vegetation cover of 0-80%) deglaciated after 1979 in the foreland of the Ecology Glacier and a Cambic Cryosol (vegetation cover of 100%) distal to the lateral moraine deglaciated before 1956 were investigated by combining soil chemical and microbiological methods. In the upper part of all soils, a decrease in soil pH was observed, but only the Cambic Cryosol showed a clear direction of pedogenic and weathering processes, such as initial silicate weathering indicated by a decreasing Chemical Index of Alteration with depth. Differences in the development of these initial soils could be related to different microbial community compositions and vegetation coverage, despite the short distance among them. We observed-decreasing with depth-the highest bacterial abundances and microbial diversity at vegetated sites. Multiple clusters of abundant amplicon sequence variants were found depending on the site-specific characteristics as well as a distinct shift in the microbial community structure towards more similar communities at soil depths > 10 cm. In the foreland of the Ecology Glacier, the main soil-forming processes on a decadal timescale are acidification and accumulation of soil organic carbon and nitrogen, accompanied by changes in microbial abundances, microbial community compositions, and plant coverage, whereas quantifiable silicate weathering and the formation of pedogenic oxides occur on a centennial to a millennial timescale after deglaciation.

The largest moss carpet transplant in Antarctica and its bryosphere cryptic biodiversity

As part of the reconstruction of the Brazilian Antarctic Station on King George Island, three areas of moss carpet were transplanted to minimize the impact of the new facilities on the local biodiversity. A total of 650 m² of moss carpet was transplanted to neighboring but previously uncolonized locations and has subsequently survived for the last 3 years. Antarctic moss carpets typically comprise low moss species diversity and are often monospecific. We investigated the cryptic biodiversity that was transplanted along with the carpets using a metabarcoding approach through high throughput sequencing. We targeted 16S rRNA for Bacteria and Archaea, ITS for Fungi and Viridiplantae and Cox1 for Metazoa. We detected DNA representing 263 taxa from five Kingdoms (Chromista, Fungi, Metazoa, Protista and Viridiplantae), two Domains (Archaea and Bacteria) and 33 Phyla associated with the carpet. This diversity included one Archaea, 189 Bacteria, 24 Chromista, 19 Fungi, eight Metazoa, seven Protista and 16 Viridiplantae. Bacteria was the most abundant, rich and diverse group, with Chromista second in diversity and richness. Metazoa was less diverse but second highest in dominance. This is the first study to attempt transplanting a significant area of moss carpet to minimize anthropogenic environmental damage in Antarctica and to use metabarcoding as a proxy to assess diversity associated with Antarctic moss carpets, further highlighting the importance of such habitats for other organisms and their importance for conservation.

Dynamics of Soil Bacterial and Fungal Communities During the Secondary Succession Following Swidden Agriculture IN Lowland Forests

Elucidating dynamics of soil microbial communities after disturbance is crucial for understanding ecosystem restoration and sustainability. However, despite the widespread practice of swidden agriculture in tropical forests, knowledge about microbial community succession in this system is limited. Here, amplicon sequencing was used to investigate effects of soil ages (spanning at least 60 years) after disturbance, geographic distance (from 0.1 to 10 km) and edaphic property gradients (soil pH, conductivity, C, N, P, Ca, Mg, and K), on soil bacterial and fungal communities along a chronosequence of sites representing the spontaneous succession following swidden agriculture in lowland forests in Papua New Guinea. During succession, bacterial communities (OTU level) as well as its abundant (OTU with relative abundance > 0.5%) and rare (<0.05%) subcommunities, showed less variation but more stage-dependent patterns than those of fungi. Fungal community dynamics were significantly associated only with geographic distance, whereas bacterial community dynamics were significantly associated with edaphic factors and geographic distance. During succession, more OTUs were consistently abundant (n = 12) or rare (n = 653) for bacteria than fungi (abundant = 6, rare = 5), indicating bacteria were more tolerant than fungi to environmental gradients. Rare taxa showed higher successional dynamics than abundant taxa, and rare bacteria (mainly from Actinobacteria, Proteobacteria, Acidobacteria, and Verrucomicrobia) largely accounted for bacterial community development and niche differentiation during succession.

In-situ soil greenhouse gas fluxes under different cryptogamic covers in maritime Antarctica

Soils can influence climate by sequestering or emitting greenhouse gases (GHG) such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). We are far from understanding the direct influence of cryptogamic covers on soil GHG fluxes, particularly in areas free of potential anthropogenic confounding factors. We assessed the role of well-developed cryptogamic covers in soil attributes, as well as in the in-situ exchange of GHG between Antarctic soils and the atmosphere during the austral summer. We found lower values of soil organic matter, total organic carbon, and total nitrogen in bare areas than in soils covered by mosses and, particularly, lichens. These differences, together with concomitant decreases and increases in soil temperature and moisture, respectively, resulted in increases in in-situ CO₂ emission (i.e. ecosystem respiration) and decreases in CH₄ uptake but no significant changes in N₂O fluxes. We found consistent linear positive and negative relationships between soil attributes (i.e. soil organic matter, total organic carbon and total nitrogen) and CO₂ emissions and CH₄ uptake, respectively, and polynomial relationships between these soil attributes and net N₂O fluxes. Our results indicate that any increase in the area occupied by cryptogams in terrestrial Antarctic ecosystems (due to increased growing season and increasingly warming conditions) will likely result in parallel increases in soil fertility as well as in an enhanced capacity to emit CO₂ and a decreased capacity to uptake CH₄. Such changes, unless offset by parallel C uptake processes, would represent a paradigmatic example of a positive climate change feedback. Further, we show that the fate of these terrestrial ecosystems under future climate scenarios, as well as their capacity to exchange GHG with the atmosphere might depend on the relative ability of different aboveground cryptogams to thrive under the new conditions.

Connectivity of Edaphic and Endolithic Microbial Niches in Cold Mountain Desert of Eastern Pamir (Tajikistan)

Microbial communities found in arid environments are commonly represented by biological soil crusts (BSCs) and endolithic assemblages. There is still limited knowledge concerning endoliths and BSCs occurring in the cold mountain desert of Pamir. The aim of the study was to investigate the composition and structure of endolithic bacterial communities in comparison to surrounding BSCs in three subregions of the Eastern Pamir (Tajikistan). The endolithic and BSC communities were studied using culture-independent and culture-dependent techniques. The structure of the endolithic bacterial communities can be characterized as Actinobacteria-Proteobacteria-Bacteroidetes-Chloroflexi-Cyanobacteria, while the BSCs' can be described as Proteobacteria-Actinobacteria-Bacteroidetes-Cyanobacteria assemblages with low representation of other bacteria. The endolithic cyanobacterial communities were characterized by the high percentage of Chroococcidiopsaceae, Nodosilineaceae, Nostocaceae and Thermosynechococcaceae, while in the BSCs were dominated by Nodosilineaceae, Phormidiaceae and Nostocaceae. The analysis of 16S rRNA genes of the cyanobacterial cultures revealed the presence of possibly novel species of Chroococcidiopsis, Gloeocapsopsis and Wilmottia. Despite the niches' specificity, which is related to the influence of microenvironment factors on the composition and structure of endolithic communities, our results illustrate the interrelation between the endoliths and the surrounding BSCs in some regions. The structure of cyanobacterial communities from BSC was the only one to demonstrate some subregional differences.

Cryptogamic cover determines soil attributes and functioning in polar terrestrial ecosystems

We still lack studies that provide evidence for direct links between the development of soil surface cryptogamic communities and soil attributes and functioning. This is particularly true in areas free of potentially confounding factors such as different soil types, land uses, or anthropogenic disturbances. Despite the ecological importance of polar ecosystems and their sensitivity to climate change, we are far from understanding how their soils function and will respond to climate change-driven alterations in above- and belowground features. We used two complementary approaches (i.e. cover gradients in the forefront of retreating glaciers as well as long-time deglaciated areas with well-developed cryptogamic cover types) to evaluate the role of cryptogams driving multiple soil biotic and abiotic attributes and functioning rates in polar terrestrial ecosystems. Increases in cryptogamic cover were consistently related to increases in organic matter accumulation, soil fertility, and bacterial diversity, but also in enhanced soil functioning rates in both sampling areas. However, we also show that the ability to influence soil attributes varies among different polar cryptogamic covers, indicating that their differential ability to thrive under climate-change scenarios will largely determine the fate of polar soils in coming decades.

Early ecological succession patterns of bacterial, fungal and plant communities along a chronosequence in a recently deglaciated area of the Italian Alps

In this study, the early ecological succession patterns of Forni Glacier (Ortles-Cevedale group, Italian Alps) forefield along an 18-year long chronosequence (with a temporal resolution of 1 year) has been reported. Bacterial and fungal community structures were inferred by high-throughput sequencing of 16S rRNA gene and ITS, respectively. In addition, the occurrence of both herbaceous and arboreous plants was also recorded at each plot. A significant decrease of alpha-diversity in more recently deglaciated areas was observed for both bacteria and plants. Time since deglaciation and pH affected the structure of both fungal and bacterial communities. Pioneer plants could be a major source of colonization for both bacterial and fungal communities. Consistently, some of the most abundant bacterial taxa and some of those significantly varying with pH along the chronosequence (Polaromonas, Granulicella, Thiobacillus, Acidiferrobacter) are known to be actively involved in rock-weathering processes due to their chemolithotrophic metabolism, thus suggesting that the early phase of the chronosequence could be mainly shaped by the biologically controlled bioavailability of metals and inorganic compounds. Fungal communities were dominated by ascomycetous filamentous fungi and basidiomycetous yeasts. Their role as cold-adapted organic matter decomposers, due to their heterotrophic metabolism, was suggested.

Diversity and Ecology of Chlorophyta (Viridiplantae) Assemblages in Protected and Non-protected Sites in Deception Island (Antarctica, South Shetland Islands) Assessed Using an NGS Approach

Assessment of the diversity of algal assemblages in Antarctica has until now largely relied on traditional microbiological culture approaches. Here we used DNA metabarcoding through high-throughput sequencing (HTS) to assess the uncultured algal diversity at two sites on Deception Island, Antarctica. The first was a relatively undisturbed site within an Antarctic Specially Protected Area (ASPA 140), and the second was a site heavily impacted by human visitation, the Whalers Bay historic site. We detected 65 distinct algal taxa, 50 from within ASPA 140 and 61 from Whalers Bay. Of these taxa, 46 were common to both sites, and 19 only occurred at one site. Algal richness was about six times greater than reported in previous studies using culture methods. A high proportion of DNA reads obtained was assigned to the highly invasive species Caulerpa webbiana at Whalers Bay, and the potentially pathogenic genus Desmodesmus was found at both sites. Our data demonstrate that important differences exist between these two protected and human-impacted sites on Deception Island in terms of algal diversity, richness, and abundance. The South Shetland Islands have experienced considerable effects of climate change in recent decades, while warming through geothermal activity on Deception Island itself makes this island one of the most vulnerable to colonization by non-native species. The detection of DNA of non-native taxa highlights concerns about how human impacts, which take place primarily through tourism and national research operations, may influence future biological colonization processes in Antarctica.

Are recently deglaciated areas at both poles colonised by the same bacteria?

Polar glacier forefields offer an unprecedented framework for studying community assembly processes in regions that are geographically and climatically isolated. Through amplicon sequence variant (ASV) inference, we compared the composition and structure of soil bacterial communities from glacier forefields in Iceland and Antarctica to assess overlap between communities and the impact of established cryptogamic covers on the uniqueness of their taxa. These pioneer microbial communities were found to share only 8% of ASVs and each taxonomic group's contribution to the shared ASV data subset was heterogeneous and independent of their relative abundance. Although the presence of ASVs specific to one glacier forefield and/or different cryptogam cover values confirms the existence of habitat specialist bacteria, our data show that the influence of cryptogams on the edaphic bacterial community structure also varied also depending on the taxonomic group. Hence, the establishment of distinct cryptogamic covers is probably not the only factor driving the uniqueness of bacterial communities at both poles. The structure of bacterial communities colonising deglaciated areas seems also conditioned by lineage-specific limitations in their dispersal capacity and/or their establishment and persistence in these isolated and hostile regions.

Distinct Microbial Communities in Adjacent Rock and Soil Substrates on a High Arctic Polar Desert

Understanding microbial niche variability in polar regions can provide insights into the adaptive diversification of microbial lineages in extreme environments. Compositions of microbial communities in Arctic soils are well documented but a comprehensive multidomain diversity assessment of rocks remains insufficiently studied. In this study, we obtained two types of rocks (sandstone and limestone) and soils around the rocks in a high Arctic polar desert (Svalbard), and examined the compositions of archaeal, bacterial, fungal, and protistan communities in the rocks and soils. The microbial community structure differed significantly between rocks and soils across all microbial groups at higher taxonomic levels, indicating that Acidobacteria, Gemmatimonadetes, Latescibacteria, Rokubacteria, Leotiomycetes, Pezizomycetes, Mortierellomycetes, Sarcomonadea, and Spirotrichea were more abundant in soils, whereas Cyanobacteria, Deinococcus-Thermus, FBP, Lecanoromycetes, Eurotiomycetes, Trebouxiophyceae, and Ulvophyceae were more abundant in rocks. Interestingly, fungal communities differed markedly between two different rock types, which is likely to be ascribed to the predominance of distinct lichen-forming fungal taxa (Verrucariales in limestone, and Lecanorales in sandstone). This suggests that the physical or chemical properties of rocks could be a major determinant in the successful establishment of lichens in lithic environments. Furthermore, the biotic interactions among microorganisms based on co-occurrence network analysis revealed that Polyblastia and Verrucaria in limestone, and Atla, Porpidia, and Candelariella in sandstone play an important role as keystone taxa in the lithic communities. Our study shows that even in niches with the same climate regime and proximity to each other, heterogeneity of edaphic and lithic niches can affect microbial community assembly, which could be helpful in comprehensively understanding the effects of niche on microbial assembly in Arctic terrestrial ecosystems.

Diversity and Colonization Strategies of Endolithic Cyanobacteria in the Cold Mountain Desert of Pamir

Microorganisms can survive in extreme environments and oligotrophic habitats thanks to their specific adaptive capacity. Due to its severe and contrasting climate conditions, the cold mountain desert in Eastern Pamir provides a unique environment for analyzing microbial adaptation mechanisms occurring within colonization of endolithic habitats. This study aims to investigate the composition and structure of endolithic microbial communities and analyze the interactions between microorganisms and colonized lithic substrates. Endolithic biofilms were examined using scanning electron microscopy in backscattered electron mode (SEM-BSE) and next-generation sequencing (NGS) applying amplicon sequence variants (ASVs) approach. The investigation of the V3–V4 region of 16S rRNA gene revealed that endolithic communities are dominated by Actinobacteria (26%), Proteobacteria (23%), and Cyanobacteria (11.4%). Cyanobacteria were represented by Oxyphotobacteria with a predominance of subclasses of Oscillatoriophycidae, Synechococcophycideae, and Nostocophycidae as well as the rarely occurring Sericytochromatia. The positive correlation between the contribution of the orders Synechococcales and Rhizobiales to community structure suggests that some functionally closed taxa of Cyanobacteria and Proteobacteria can complement each other, for example, in nitrogen fixation in endolithic communities. The endolithic communities occurring in Eastern Pamir were identified as complex systems whose composition and structure seem to be influenced by the architecture of microhabitats and related microenvironmental conditions.

The wasted chewing gum bacteriome

Here we show the bacteriome of wasted chewing gums from five different countries and the microbial successions on wasted gums during three months of outdoors exposure. In addition, a collection of bacterial strains from wasted gums was set, and the biodegradation capability of different gum ingredients by the isolates was tested. Our results reveal that the oral microbiota present in gums after being chewed, characterised by the presence of species such as Streptococcus spp. or Corynebacterium spp., evolves in a few weeks to an environmental bacteriome characterised by the presence of Acinetobacter spp., Sphingomonas spp. and Pseudomonas spp. Wasted chewing gums collected worldwide contain a typical sub-aerial biofilm bacteriome, characterised by species such as Sphingomonas spp., Kocuria spp., Deinococcus spp. and Blastococcus spp. Our findings have implications for a wide range of disciplines, including forensics, contagious disease control, or bioremediation of wasted chewing gum residues.

Microbial Nitrogen Cycling in Antarctic Soils

The Antarctic continent is widely considered to be one of the most hostile biological habitats on Earth. Despite extreme environmental conditions, the ice-free areas of the continent, which constitute some 0.44% of the total continental land area, harbour substantial and diverse communities of macro-organisms and especially microorganisms, particularly in the more "hospitable" maritime regions. In the more extreme non-maritime regions, exemplified by the McMurdo Dry Valleys of South Victoria Land, nutrient cycling and ecosystem servicing processes in soils are largely driven by microbial communities. Nitrogen turnover is a cornerstone of ecosystem servicing. In Antarctic continental soils, specifically those lacking macrophytes, cold-active free-living diazotrophic microorganisms, particularly Cyanobacteria, are keystone taxa. The diazotrophs are complemented by heterotrophic bacterial and archaeal taxa which show the genetic capacity to perform elements of the entire N cycle, including nitrification processes such as the anammox reaction. Here, we review the current literature on nitrogen cycling genes, taxa, processes and rates from studies of Antarctic soils. In particular, we highlight the current gaps in our knowledge of the scale and contribution of these processes in south polar soils as critical data to underpin viable predictions of how such processes may alter under the impacts of future climate change.

Biodiversity of Trichoderma from grassland and forest ecosystems in Northern Xinjiang, China

Trichoderma spp., a cosmopolitan fungal genus, has remarkable economic value in industry and agriculture. The resources of Trichoderma spp. in the grassland and forest ecosystems of northern Xinjiang were explored in this study. A total of 634 soil samples was collected, and 312 strains assigned to 23 species of Trichoderma spp. were identified. T. harzianum was the dominant species with 28.2% from all isolates. The principal components analysis indicated that ecosystem was the most dominant impact factor among longitude, latitude, altitude and ecosystems for the species diversities of Trichoderma spp. with the decreasing trend from the north to the south of northern Xinjiang (e.g., from Altay, followed by Yili, Changji, Bayingolin and finally Urumqi). Overall, Trichoderma spp. were more frequently encountered in forest ecosystems (coniferous forest and coniferous and broadleaf mixed forest) than in grassland ecosystems (desert steppe and temperate steppe). Frequency of Trichoderma spp. was significantly decreased along with increased altitude and only a few strains were isolated from altitudes above 3000 m. The results provided essential information on Trichoderma occurrence and distribution, which should benefit the application of Trichoderma in agriculture.