Permafrost thaw with warming reduces microbial metabolic capacities in subsurface soils

Effects of simulated warming on soil microbial community diversity and composition across diverse ecosystems

Soil warming can directly affect the microbial community, or indirectly affect the microbial community by affecting soil moisture, nutrient availability, vegetation growth, etc. However, the response of microorganisms to soil warming is complex, and there is no uniform conclusion on the impact and mechanism of warming on microbial diversity. As the global climate gradually warms, a comprehensive assessment of warming on soil microbial community changes is essential to understand and predict the response of microbial geochemical processes to soil warming. Here, we perform a meta-analysis of studies to investigate changes in soil microbial communities along soil warming gradients and the response of soil microbes to elevated temperature in different ecosystems. We found that the α diversity index of soil microorganisms decreased significantly with the increase in temperature, and the β diversity altered with the increase in soil temperature and the shifts in ecosystem. Most bacteria only alter when the temperature rises higher. Compared to the non-warming condition, the relative abundance of Acidobacteria, Proteobacteria, Bacteroidetes, Planctomycetes and Verrucomicrobia decreased by 19 %, 11 %, 19 %, 8 % and 6 %, respectively, and the relative abundance of Firmicutes increased by 34 %. Compared to farmland, forest, grassland and tundra ecosystems, soil microorganisms in wetland ecosystems were more sensitive to temperature increase, and the changes in bacteria were consistent with the overall alterations. This meta-analysis revealed significant changes in the composition of microbial communities on soil warming. With the decrease in biodiversity under increasing temperature conditions, these dominant microbiomes, which can grow well under high-temperature conditions, will play a stronger role in regulating nutrient and energy flow. Our analysis adds a global perspective to the temperature response of soil microbes, which is critical to improving our understanding of the mechanisms of how soil microbes change in response to climate warming.

Molecular ecology of microbiomes in the wild: Common pitfalls, methodological advances and future directions

The study of microbiomes across organisms and environments has become a prominent focus in molecular ecology. This perspective article explores common challenges, methodological advancements, and future directions in the field. Key research areas include understanding the drivers of microbiome community assembly, linking microbiome composition to host genetics, exploring microbial functions, transience and spatial partitioning, and disentangling non-bacterial components of the microbiome. Methodological advancements, such as quantifying absolute abundances, sequencing complete genomes, and utilizing novel statistical approaches, are also useful tools for understanding complex microbial diversity patterns. Our aims are to encourage robust practices in microbiome studies and inspire researchers to explore the next frontier of this rapidly changing field.

Opening Pandora's Box: Neglected Biochemical Potential of Permafrost-Associated Fungal Communities in a Warming Climate

Permafrost, a vast storage reservoir of frozen organic matter, is rapidly thawing due to climate change, releasing previously preserved carbon into the environment. This phenomenon has significant consequences for microbial communities, including fungi, inhabiting permafrost-associated regions. In this review, we delve into the intricate interplay between permafrost thawing and fungal diversity and functionality with an emphasis on thermokarst lakes. We explore how the release of organic carbon from thawing permafrost alters the composition and activities of fungal communities, emphasizing the potential for shifts in taxonomic diversity and functional gene expression. We discuss the formation of thermokarst lakes, as an example of permafrost thaw-induced ecological disruptions and their impact on fungal communities. Furthermore, we analyze the repercussions of these changes, including effects on nutrient cycling, plant productivity, and greenhouse gas (GHG) emissions. By elucidating the multifaceted relationship between permafrost thaw and aquatic fungi, this review provides valuable insights into the ecological consequences of ongoing climate change in permafrost-affected regions.

Responses of soil microbes and enzymes to long-term warming incubation in different depths of permafrost peatland soil

Soil microbes and enzymes mediate soil carbon-climate feedback, and their responses to increasing temperature partly affect soil carbon stability subjected to the effects of climate change. We performed a 50-month incubation experiment to determine the effect of long-term warming on soil microbes and enzymes involved in carbon cycling along permafrost peatland profile (0-150 cm) and investigated their response to water flooding in the active soil layer. Soil bacteria, fungi, and most enzymes were observed to be sensitive to changes in temperature and water in the permafrost peatland. Bacterial and fungal abundance decreased in the active layer soil but increased in the deepest permafrost layer under warming. The highest decrease in the ratio of soil bacteria to fungi was observed in the deepest permafrost layer under warming. These results indicated that long-term warming promotes recalcitrant carbon loss in permafrost because fungi are more efficient in decomposing high-molecular-weight compounds. Soil microbial catabolic activity measured using Biolog Ecoplates indicated a greater degree of average well color development at 15 °C than at 5 °C. The highest levels of microbial catabolic activity, functional diversity, and carbon substrate utilization were found in the permafrost boundary layer (60-80 cm). Soil polyphenol oxidase that degrades recalcitrant carbon was more sensitive to increases in temperature than β-glucosidase, N-acetyl-β-glucosaminidase, and acid phosphatase, which degrade labile carbon. Increasing temperature and water flooding exerted a synergistic effect on the bacterial and fungal abundance and β-glucosidase, acid phosphatase, and RubisCO activity in the topsoil. Structural equation modeling analysis indicated that soil enzyme activity significantly correlated with ratio of soil bacteria to fungi and microbial catabolic activity. Our results provide valuable insights into the linkage response of soil microorganisms, enzymes to climate change and their feedback to permafrost carbon loss.

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.

Tundra Soil Viruses Mediate Responses of Microbial Communities to Climate Warming

The rise of global temperature causes the degradation of the substantial reserves of carbon (C) stored in tundra soils, in which microbial processes play critical roles. Viruses are known to influence the soil C cycle by encoding auxiliary metabolic genes and infecting key microorganisms, but their regulation of microbial communities under climate warming remains unexplored. In this study, we evaluated the responses of viral communities for about 5 years of experimental warming at two depths (15 to 25 cm and 45 to 55 cm) in the Alaskan permafrost region. Our results showed that the viral community and functional gene composition and abundances (including viral functional genes related to replication, structure, infection, and lysis) were significantly influenced by environmental conditions such as total nitrogen (N), total C, and soil thawing duration. Although long-term warming did not impact the viral community composition at the two depths, some glycoside hydrolases encoded by viruses were more abundant at both depths of the warmed plots. With the continuous reduction of total C, viruses may alleviate methane release by altering infection strategies on methanogens. Importantly, viruses can adopt lysogenic and lytic lifestyles to manipulate microbial communities at different soil depths, respectively, which could be one of the major factors causing the differences in microbial responses to warming. This study provides a new ecological perspective on how viruses regulate the responses of microbes to warming at community and functional scales. IMPORTANCE Permafrost thawing causes microbial release of greenhouse gases, exacerbating climate warming. Some previous studies examined the responses of the microbial communities and functions to warming in permafrost region, but the roles of viruses in mediating the responses of microbial communities to warming are poorly understood. This study revealed that warming induced changes in some viral functional classes and in the virus/microbe ratios for specific lineages, which might influence the entire microbial community. Furthermore, differences in viral communities and functions, along with soil depths, are important factors influencing microbial responses to warming. Collectively, our study revealed the regulation of microbial communities by viruses and demonstrated the importance of viruses in the microbial ecology research.

Warming changes the composition and diversity of fungal communities in permafrost

Purpose

It is the data support and theoretical basis for the response mechanism of soil fungi to climate warming in permafrost areas in the Greater Xing’an Mountains.

Methods

We collected permafrost from the Greater Xing’an Mountains for indoor simulation experiments and took the natural permafrost as the control (CK) and the test groups of 0 °C (T1), 2 °C (T2), and 4 °C (T3) were set. Illumina MiSeq high-throughput sequencing technology was used to understand the changes in characteristics of fungal communities, and the correlations were analyzed combined with the soil physicochemical properties.

Results

Compared with CK, the value of pH and the content of available potassium (AK) in the three warming treatment groups were significantly lower (P < 0.05), and the microbial biomass carbon (MBC) content was significantly higher (P < 0.05). The content of total nitrogen (TN) and available nitrogen (AN) in the T1 and T3 groups was significantly lower than that in the CK group (P < 0.05). A total of 11 phyla, 39 classes, 89 orders, 187 families, 361 genera, and 522 species were obtained through fungal sequencing and divided into 1463 amplicon sequence variants (ASVs). Ascomycota and Dimorphospora were the dominant phylum and genus, respectively, and there were differences in the response of relative abundance of various groups at the phylum and genus levels to warming. Warming significantly decreased the Sobs and ACE indexes of the treatment groups (P < 0.05), and the Shannon and Shannoneven indexes also showed a downward trend. Moreover, warming significantly changed the fungal beta diversity (P < 0.01), while the value of pH and the content of TN, MBC, and AK could significantly affect the community structure (P < 0.05), and the correlation between fungi at different phyla levels and soil physicochemical properties was different.

Conclusions

These results can provide a reference for further study on the changes in composition and structure of fungal communities and the influence factor in permafrost in the Greater Xing’an Mountains under the background of warming.

Bacterial functional redundancy and carbon metabolism potentials in soil, sediment, and water of thermokarst landscapes across the Qinghai-Tibet Plateau: Implications for the fate of permafrost carbon

Permafrost thaw create widespread thermokarst landscapes. As a result, distinct habitats are provided to harbor different bacterial communities in degraded permafrost soil (PBCs), thermokarst lake sediment (SBCs), and lake water (WBCs), driving carbon metabolism differentially. In this study, we investigated functional diversity and redundancy, and carbon metabolism potentials of PBCs, SBCs, and WBCs in thermokarst landscapes across the Qinghai-Tibet Plateau. The results showed that PBCs and SBCs had higher taxonomic and functional alpha diversity than WBCs, while WBCs had lower functional redundancy. WBCs had the highest beta diversity followed by SBCs and PBCs, suggesting strong determination of taxonomic variations on functional differences. Community assembly processes also had significant influences on beta diversity, especially for SBCs. Metabolism pathways of carbohydrate metabolism, methane metabolism, and carbon fixation were enriched differentially in PBCs, SBCs, and WBCs, suggesting different C fate in distinct habitats. Carbohydrate metabolism data suggested that PBCs might have stronger potentials to mineralize a greater diversity of organic carbon substrate than SBCs and WBCs, promoting degradation of organic carbon stocks in degraded permafrost soils. Methane metabolism data showed that SBCs had a stronger methanogenesis potential followed by PBCs and WBCs, while PBCs had a stronger methane oxidation potential. High abundance of genes involving in formaldehyde assimilation might suggested that a large proportion of produced methane might be assimilated by methanotrophs in the thermokarst landscapes. Both aerobic and anaerobic carbon fixation pathways were enriched in PBCs. The results added our understanding of functional properties and biogeochemical carbon cycles in thermokarst landscapes, improving our abilities in accurate modeling of carbon dynamics and the ultimate fate of permafrost carbon in a warming world.

Soil CO2 and N2O emissions and microbial abundances altered by temperature rise and nitrogen addition in active-layer soils of permafrost peatland

Changes in soil CO₂ and N₂O emissions due to climate change and nitrogen input will result in increased levels of atmospheric CO₂ and N₂O, thereby feeding back into Earth's climate. Understanding the responses of soil carbon and nitrogen emissions mediated by microbe from permafrost peatland to temperature rising is important for modeling the regional carbon and nitrogen balance. This study conducted a laboratory incubation experiment at 15 and 20°C to observe the impact of increasing temperature on soil CO₂ and N₂O emissions and soil microbial abundances in permafrost peatland. An NH₄NO₃ solution was added to soil at a concentration of 50 mg N kg^-1 to investigate the effect of nitrogen addition. The results indicated that elevated temperature, available nitrogen, and their combined effects significantly increased CO₂ and N₂O emissions in permafrost peatland. However, the temperature sensitivities of soil CO₂ and N₂O emissions were not affected by nitrogen addition. Warming significantly increased the abundances of methanogens, methanotrophs, and nirK-type denitrifiers, and the contents of soil dissolved organic carbon (DOC) and ammonia nitrogen, whereas nirS-type denitrifiers, β-1,4-glucosidase (βG), cellobiohydrolase (CBH), and acid phosphatase (AP) activities significantly decreased. Nitrogen addition significantly increased soil nirS-type denitrifiers abundances, β-1,4-N- acetylglucosaminidase (NAG) activities, and ammonia nitrogen and nitrate nitrogen contents, but significantly reduced bacterial, methanogen abundances, CBH, and AP activities. A rising temperature and nitrogen addition had synergistic effects on soil fungal and methanotroph abundances, NAG activities, and DOC and DON contents. Soil CO₂ emissions showed a significantly positive correlation with soil fungal abundances, NAG activities, and ammonia nitrogen and nitrate nitrogen contents. Soil N₂O emissions showed positive correlations with soil fungal, methanotroph, and nirK-type denitrifiers abundances, and DOC, ammonia nitrogen, and nitrate contents. These results demonstrate the importance of soil microbes, labile carbon, and nitrogen for regulating soil carbon and nitrogen emissions. The results of this study can assist simulating the effects of global climate change on carbon and nitrogen cycling in permafrost peatlands.

The Coupling Response between Different Bacterial Metabolic Functions in Water and Sediment Improve the Ability to Mitigate Climate Change

Extreme climatic events, such as heat wave and large temperature fluctuations, are predicted to increase in frequency and intensity during the next hundred years, which may rapidly alter the composition and function of lake bacterial communities. Here, we conducted a year-long experiment to explore the effect of warming on bacterial metabolic function of lake water and sediment. Predictions of the metabolic capabilities of these communities were performed with FAPROTAX using 16S rRNA sequencing data. The results indicated that the increase in temperature changed the structure of bacterial metabolic functional groups in water and sediment. During periods of low temperature, the carbon degradation pathway decreased, and the synthesis pathway increased, under the stimulation of warming, especially under the conditions temperature fluctuation. We also observed that nitrogen fixation ability was especially important in the warming treatments during the summer season. However, an elevated temperature significantly led to reduced nitrogen fixation abilities in winter. Compared with the water column, the most predominant functional groups of nitrogen cycle in sediment were nitrite oxidation and nitrification. Variable warming significantly promoted nitrite oxidation and nitrification function in winter, and constant warming was significantly inhibited in spring, with control in sediments. Co-occurrence network results showed that warming, especially variable warming, made microbial co-occurrence networks larger, more connected and less modular, and eventually functional groups in the water column and sediment cooperated to resist warming. We concluded that warming changed bacterial functional potentials important to the biogeochemical cycling in the experimental mesocosms in winter and spring with low temperature. The effect of different bacteria metabolism functions in water column and sediment may change the carbon and nitrogen fluxes in aquatic ecosystems. In conclusion, the coupling response between different bacterial metabolic functions in water and sediment may improve the ability to mitigate climate change.