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Abstract. Soil microbes play a crucial role in the carbon (C) cycle; however, they have been overlooked in predicting the terrestrial C cycle. We applied a microbial-explicit Earth system model – the Community Land Model-Microbe (CLM-Microbe) – to investigate the dynamics of soil microbes during 1901 to 2016. The CLM-Microbe model was able to reproduce the variations of gross (GPP) and net (NPP) primary productivity, heterotrophic (HR) and soil (SR) respiration, microbial (MBC) biomass C in fungi (FBC) and bacteria (BBC) in the top 30 cm and 1 m, and dissolved (DOC) and soil organic C (SOC) in the top 30 cm and 1 m during 1901–2016. During the study period, simulated C variables increased by approximately 12 PgC yr−1 for HR, 25 PgC yr−1 for SR, 1.0 PgC for FBC and 0.4 PgC for BBC in 0–30 cm, and 1.2 PgC for FBC and 0.7 PgC for BBC in 0–1 m. Increases in microbial C fluxes and pools were widely found, particularly at high latitudes and in equatorial regions, but we also observed their decreases in some grids. Overall, the area-weighted averages of HR, SR, FBC, and BBC in the top 1 m were significantly correlated with those of soil moisture and soil temperature in the top 1 m. These results suggested that microbial C fluxes and pools were jointly governed by vegetation C input and soil temperature and moisture. Our simulations revealed the spatial and temporal patterns of microbial C fluxes and pools in response to environmental change, laying the foundation for an improved understanding of soil microbial roles in the global terrestrial C cycle. 

The positive Arctic–methane (CH₄) feedback forms when more CH₄is released from the Arctic tundra to warm the climate, further stimulating the Arctic to emit CH₄. This study utilized the CLM-Microbe model to project CH₄emissions across five distinct Arctic tundra ecosystems on the Alaska North Slope, considering three Shared Socioeconomic Pathway (SSP) scenarios using climate data from three climate models from 2016 to 2100. Employing a hyper-resolution of 5 m × 5 m within 40,000 m²domains accounted for the Arctic tundra’s high spatial heterogeneity; three sites were near Utqiaġvik (US-Beo, US-Bes, and US-Brw), with one each in Atqasuk (US-Atq) and Ivotuk (US-Ivo). Simulated CH₄emissions substantially increased by a factor of 5.3 to 7.5 under the SSP5–8.5 scenario compared to the SSP1–2.6 and SSP2–4.5 scenarios. The projected CH₄emissions exhibited a stronger response to rising temperature under the SSP5–8.5 scenario than under the SSP1–2.6 and SSP2–4.5 scenarios, primarily due to strong temperature dependence and the enhanced precipitation-induced expansion of anoxic conditions that promoted methanogenesis. The CH₄transport via ebullition and plant-mediated transport is projected to increase under all three SSP scenarios, and ebullition dominated CH₄transport by 2100 across five sites. Projected CH₄emissions varied in temperature sensitivity, with a Q₁₀range of 2.7 to 60.9 under SSP1–2.6, 3.8 to 17.6 under SSP2–4.5, and 5.7 to 17.2 under SSP5–8.5. Compared with the other three sites, US-Atq and US-Ivo were estimated to have greater increases in CH₄emissions due to warmer temperatures and higher precipitation. The fact that warmer sites and warmer climate scenarios had higher CH₄emissions suggests an intensified positive Arctic–CH₄feedback in the 21st century. Microbial physiology and substrate availability dominated the enhanced CH₄production. The simulated intensified positive feedback underscores the urgent need for a more mechanistic understanding of CH₄dynamics and the development of strategies to mitigate CH₄across the Arctic. 

Abstract The theory of microbial stoichiometry can predict the proportional coupling of microbial assimilation of carbon (C), nitrogen (N), and phosphorus (P). The proportional coupling is quantified by the homeostasis value (H). Covariation of H values for C, N, and P indicates that microbial C, N, and P assimilation are coupled. Here, we used a global dataset to investigate the spatiotemporal dynamics of H values of microbial C, N, and P across biomes. We found that land use and management led to the decoupling of P from C and N metabolism over time and across space. Results from structural equation modeling revealed that edaphic factors dominate the microbial homeostasis of P, while soil elemental concentrations dominate the homeostasis of C and N. This result was further confirmed using the contrasting factors on microbial P vs. microbial C and N derived from a machine-learning algorithm. Overall, our study highlights the impacts of management on shifting microbial roles in nutrient cycling. 

IntroductionSurface soil microbial communities are directly exposed to the heat from wildland fires. Due to this, the microbial community composition may be stratified within the soil profile with more heat tolerant microbes near the surface and less heat tolerant microbes, or mobile species found deeper in the soil. Biological soil crusts, biocrusts, are found on the soil surface and contain a diverse microbial community that is directly exposed to the heat from wildland fires. MethodsHere, we used a simulated fire mesocosm along with a culture-based approach and molecular characterization of microbial isolates to understand the stratification of biocrust and bare soil microbes after low severity (450°C) and high severity (600°C) fires. We cultured and sequenced microbial isolates from 2 to 6 cm depth from both fire types. ResultsThe isolates were stratified along the soil depth. Green algal isolates were less thermotolerant and found in the deeper depths (4–6 cm) and the control soils, while several cyanobacteria in Oscillatoriales, Synechococcales, and Nostocales were found at 2–3 cm depth for both fire temperatures. An Alphaproteobacteria isolate was common across several depths, both fire types, and both fire temperatures. Furthermore, we used RNA sequencing at three depths after the high severity fire and one control to determine what microbial community is active following a fire. The community was dominated by Gammaproteobacteria, however some Cyanobacteria ASVs were also present. DiscussionHere we show evidence of stratification of soil and biocrust microbes after a fire and provide evidence that these microbes are able to survive the heat from the fire by living just below the soil surface. This is a steppingstone for future work on the mechanisms of microbial survival after fire and the role of soil insulation in creating resilient communities. 

We applied a microbial-explicit model – the CLM-Microbe – to investigate the dynamics of C in vegetation, litter, soil, and microbes during 1901-2016. The CLM-Microbe model was able to reproduce global averages and latitudinal trends of gross (GPP) and net (NPP) primary productivity, heterotrophic (HR) and soil (SR) respiration, biomass C in fungi (FBC) and bacteria (BBC) in the top 30 cm and 1 m, dissolved (DOC) and soil organic C (SOC) in the top 30 cm and 1 m. In addition, the CLM-Microbe model captured the grid-level variation in GPP (R2=0.78), NPP (R2=0.63), SR (R2=0.26), HR (R2=0.23), DOC in 0-30 cm (R2=0.2) and 0-1 m (R2=0.22), SOC in 0-30 cm (R2=0.36) and 0-1 m (R2=0.26), FBC (R2=0.22) and BBC (R2=0.32) in 0-30 cm, and MBC in 0-1 m (R2=0.21). From the 1900s to 2007-2016, simulated C variables increased by approximately 30 PgC yr-1 for GPP, 15 PgC yr-1 for NPP, 12 PgC yr-1 for HR, 25 PgC yr-1 for SR, 1.0 PgC for FBC and 0.4 PgC for BBC in 0-30 cm, 1.5 PgC for FBC, 0.8 PgC for BBC, 2.5 PgC for DOC, 40 PgC for SOC, and 5 PgC for litter C in 0-1 m, and 40 PgC for vegetation C. The relative increases in C fluxes and pools varied across the globe. Increases in vegetation C were closely related to warming and increased precipitation, while C accumulation in microbes and soils was jointly governed by vegetation C input and soil temperature and moisture. 

When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This project investigates the microbes that are metabolically active in the unfrozen layer during the fall zero curtain period and compares this community to that which is active in the late summer at the same depth (10-20 centimeters (cm)). This dataset contains the abundance and taxonomic designation of distinct 16S ribosomal ribonucleic acid (16S rRNA) sequences (operational taxonomic units, OTU's) associated with samples in this study. These data complement the sequences and metadata deposited in GenBank Bioproject PRJNA780202. 

When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This experiment compares the temperature response of the methanogenic community in the zero curtain period with that of the summer community to test whether the zero curtain methanogenic community is especially cold adapted. This dataset includes methane production rates measured in anaerobic laboratory incubations of soils collected from two dates (July and Nov 2018) at temperatures around 0, 4 and 10C. 

When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This project investigates the methanogenic Archaea that are metabolically active in the unfrozen layer during the fall zero curtain period and compares this community to that which is active in the late summer at the same depth (10-20 centimeters (cm)). This dataset contains the abundance of distinct partial mcrA (Methyl-coenzyme M reductase alpha subunit) gene sequences (operational taxonomic units, OTU's defined at 16% similarity) amplified from messenger ribonucleic acid (mRNA) extracted from soil samples in this study. These data complement the sequences deposited in GenBank (accession numbers OL505703-OL505708). 

An isotopic labeling experiment was conducted in an Arctic coastal wet tundra ecosystem to determine how quickly acetate is transformed into methane and transported from the soil to the atmosphere. Carbon-13 (13C) labelled acetate was injected into soil chambers installed across a 131 meter (m) transect. Gas samples were periodically collected from the headspace in chambers, and analyzed for methane concentration and enrichment in 13C. Methane flux was roughly estimated from the final concentration in the chambers accumulated over a one-hour sampling period. This dataset includes methane fluxes, concentrations and 13C enrichment values from this experiment. In addition, water samples were collected from 15 centimeters (cm) depth after the final time point for measurements of residual dissolved 13C-methane in the soil after 9 days.