Glacial retreat due to global warming is exposing large tracts of barren glacial sediments that are quickly colonized by CO2-fixing microbial communities that can constitute the climax community in many high-Arctic, alpine, and Antarctic environments. Despite the potential importance of these processes, little is known about microbial community successional dynamics and rates of carbon (C) sequestration in environments where higher plants are slow or unable to establish. We analyzed microbial community succession and C and N accumulation in newly exposed sediments along an Antarctic glacial chronosequence where moss and microbial autotrophs are the dominant primary producers. During the first 4 years of succession (0 to 40 m from the glacier) algae (including diatoms) were the most relatively abundant eukaryotes, but by the second phase studied (8 to 12 years) moss amplicon sequence variants (ASVs) dominated. The rise in moss coincided with a significant buildup of C and N in the sediments. The final two phases of the successional sequence (16 to 20 and 26 to 30 years) were marked by declines in microbial species richness and moss relative abundance, that coincided with significant decreases in both total C and N. These retrogressive declines coincided with a large increase in relative abundance of predatory Vampyrellidae suggesting a possible mechanism for retrogression in this and perhaps other terrestrial ecosystems at the edge of the cryosphere. These findings have implications for understanding CO2 sequestration and ecosystem succession in microbial-dominated regions of the cryobiosphere where large tracts of land are currently undergoing deglaciation.

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg ‧ha  1 ‧a  1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Global warming is profoundly altering soil freeze -thaw cycle (FTC) patterns, and the formation of different thicknesses and durations of snow cover by snowfall results in heterogeneity of environmental and biological factors, which can have complex effects on soil water and carbon cycle processes. In order to better develop rational regulation strategies to increase the potential of soil carbon sequestration and emission reductions under climate change conditions, a three-year in situ control trial of field snow was set up to simulate climate scenarios using two treatments: snow removal and natural snow. The effects of FTCs and biochar on soil CO 2 emission flux (CO 2 Flux) were analyzed by constructing a driven coupling model between soil hydrothermal environmental factors, unstable organic carbon components and stable organic carbon components. The results showed that CO 2 Flux decreased by 9.36% to 11.34% for 1% biochar treatment, while CO 2 Flux increased by 15.41% to 18.32% for 2% biochar treatment. Moreover, the snow removal treatment increased CO 2 Flux by 9.86% to 13.99% compared to the natural snow treatment. The snow during freezing and thawing has a dual effect on soil hydrothermal dynamics, with snow removal making the freeze -thaw action more intense in perturbing the soil carbon matrix, while the interfacial behavior of biochar with soil minerals protects the stability of the soil structure. Biochar reduces soil carbon emissions thanks to its highly stabilized components and unique surface structure, which enhances the carbon sequestration and emission reduction effect by increasing the proportion of inert organic carbon, promoting the formation of organic -inorganic complexes, and encapsulating and adsorbing soil organic matter. The results of the study can provide important theoretical support and practical models for the assessment of the environmental effects of biochar and the reduction of carbon sequestration in agriculture under climate change conditions.

Permafrost regions play an important role in global carbon and nitrogen cycling, storing enormous amounts of organic carbon and preserving a delicate balance of nutrient dynamics. However, the increasing frequency and severity of wildfires in these regions pose significant challenges to the stability of these ecosystems. This review examines the effects of fire on chemical, biological, and physical properties of permafrost regions. The physical, chemical, and pedological properties of frozen soil are impacted by fires, leading to changes in soil structure, porosity, and hydrological functioning. The combustion of organic matter during fires releases carbon and nitrogen, contributing to greenhouse gas emissions and nutrient loss. Understanding the interactions between fire severity, ecosystem processes, and the implications for permafrost regions is crucial for predicting the impacts of wildfires and developing effective strategies for ecosystem protection and agricultural productivity in frozen soils. By synthesizing available knowledge and research findings, this review enhances our understanding of fire severity's implications for permafrost ecosystems and offers insights into effective fire management strategies.

Simple Summary Microorganisms and their enzymes are crucial to ensuring soil quality, health, and carbon sequestration. Their numerous reactions are essential for biogeochemical cycles. However, a comprehensive review is lacking to summarize the latest findings in agricultural and enzymatic research. Although the relationships between soil enzyme activities and different soil ecosystems, such as arctic and permafrost regions, tropics and subtropics, tundra, steppes, etc., have been intensively investigated, particularly in the context of climate changes, only a few reviews summarize the impact of climate change on soil enzyme activity. This review aims to highlight the main groups of microbial enzymes found in soil (such as alpha-glucosidases and beta-glucosidases, phosphatases, ureases, N-acetyl-glucosaminidases, peptidases, etc.), their role in the global nutrient cycles of carbon, nitrogen, phosphorus, sulfur, carbon sequestration, and the influence of intensive agriculture on microbial enzymatic activity, and the variations in enzyme activity across different climate zones and soil ecosystems. Furthermore, the review will emphasize the importance of microbial enzymes for soil fertility and present both current challenges and future perspectives.Abstract The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg ‧ha  1 ‧a  1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Polar ecosystems are the most important storage and source of climatically active gases. Currently, natural biogeochemical processes of organic matter circulation in the soil-atmosphere system are disturbed in urban ecosystems of the cryolithozone. Urbanized ecosystems in the Arctic are extremely under-investigated in terms of their functions in regulating the cycle of climatically active gases. The role of urban soils and soil-like bodies in the sequestration and stabilization of organic matter is of particular interest. The percentage of gravimetric concentrations of organic matter in Arctic urban soils are almost always determined by the method of dichromate oxidation and are subject to extreme variability (from tenths of a percent to more than 90% in man-made soil formations), but the average carbon content in the surface soil horizons can be estimated at 5-7%. The surface humus-accumulative horizons are represented by a variety of morphological forms with the content of organic matter of various origins. The work also focuses on those forms of organic matter, the content of which is extremely small, but very important for the biogeochemical functioning of soils-polycyclic aromatic hydrocarbons and components of petroleum products, as well as labile forms of soil organic matter. We recommend that further studies of the organic matter system be conducted in urbanized areas since the carbon cycle there is severely disrupted, as well as carbon flows. The urbanization and industrialization processes in the Arctic are progressing, which could lead to a radical transformation of carbon ecosystem services.

Purpose Warming-induced permafrost degradation is anticipated to change the global carbon cycle. We attempted to determine the effect of permafrost degradation on carbon emissions and carbon sequestration of seven wetlands in three zones of Northeast China, aiming to investigate the responses of carbon sources/sinks to permafrost degradation. Methods Three zones (permafrost zone, PZ; discontinuous permafrost zone, DPZ; and permafrost degradation zone, PDZ) were selected to represent permafrost degradation stages. In each zone, we selected seven wetlands along the moisture gradient, namely, marsh (M), thicket swamp (TS), forested swamps (alder swamp, FAS; birch swamp, FBS; and larch swamp, FLS), forested fen (larch fen, FLF), and forested bog (larch bog, FLB). We determined the annual carbon emissions of soil heterotrophic respiration from seven wetlands and the annual net carbon sequestration of vegetation, evaluated the net carbon balance by calculating the difference between annual net carbon sequestration and annual carbon emissions, and then determined the magnitude and direction of carbon-climate feedback. Results and discussion With permafrost degradation, most forested wetlands (excluding FAS in PDZ) still acted as carbon sinks in DPZ (0.30 - 1.88 t ha(-1) year(-1)) and PDZ (0.31 - 1.76 t ha(-1) year(-1)) in comparison to PZ (0.46 - 2.43 t ha(-1) year(-1)). In contrast, M and TS acted as carbon sources in DPZ (-1.72 and -0.82 t ha(-1) year(-1)) and PDZ (-2.66 and -0.98 t ha(-1) year(-1)) in comparison to PZ (-0.86 and 0.03 t ha(-1) year(-1)), this result could be attributed to the increased CO2 emissions (promoted by warmer soil temperatures) and CH4 emissions (promoted by warmer soil temperatures, higher water tables and greater thaw depths), the two significantly increased the annual carbon emissions (increased by 8.8 - 14.4% in DPZ and by 35.0 - 46.0% in PDZ), and the annual carbon emissions > the annual net carbon sequestration. Furthermore, in terms of net radiative forcing, five forested wetlands still showed negative net radiative forcing in DPZ (-6.90 to -1.10 t CO2-eq ha(-1) year(-1)) in comparison to PZ (-8.91 to -1.62 t CO2-eq ha(-1) year(-1)). In contrast, in PDZ, only FLB showed negative net radiative forcing (-6.29 t CO2-eq ha(-1) year(-1)) and significantly increased by 288.3% compared to PZ (P < 0.05), indicating an ever-increasing net cooling impact, while the other four forested wetlands all turned into positive net radiative forcing (0.84 - 53.56 t CO2-eq ha(-1) year(-1)) because of higher CH4 (CO2-eq) emissions, indicating net warming impacts. Conclusions Our results indicated that permafrost degradation affected the carbon sources/sinks of seven wetlands via different mechanisms. M and TS acted as carbon sources in both DPZ and PDZ, while permafrost degradation did not change the overall direction of the net carbon balance of five forested wetlands. Most forested wetlands (excluding FAS in PDZ) still acted as carbon sinks in both DPZ and PDZ, although there were fluctuations in carbon sink values. Moreover, despite being carbon sinks, most forested wetlands (excluding FLB) in PDZ showed positive net radiative forcing compared to DPZ and PZ (negative net radiative forcing) when using the methodology of CO2 equivalent, indicating climatic warming impacts, while FLB showed negative net radiative forcing, indicating a climatic cooling impact. Therefore, FLB should be protected as a priority in the subsequent carbon sink management practices in permafrost zones.

Development of carbon polygons for monitoring the emission and deposition of carbon compounds in terrestrial ecosystems is one of the priority tasks in the case of climate and biosphere conservation. Significant is the role of soils, which are not only the main source of greenhouse gas emissions into the Earth's atmosphere but also a long-term reservoir that stores significant amounts of organic carbon in the form of soil humus. The article discusses the organization of monitoring of greenhouse gases at carbon polygons, the methods of sampling soil horizons, and methodological approaches to determine the content and stocks of organic carbon in soils. The importance of information on the qualitative and quantitative composition of soil organic matter and humic substances, which is necessary for the operation of modern simulation models and calculation of carbon units for the economic assessment of the direct and reverse carbon footprint have been revealed. Russia faces a number of challenges related to carbon offset and a low-carbon economy. The necessary volumes of monitoring data, which must be obtained at carbon polygons for the use of the ROMUL and Efimod models are considered. The necessity for an adequate spatial coverage of the territory of Russia with a network of carbon polygons is emphasized. Particular attention should be paid to the arctic territories that contain significant amounts of organic matter in permafrost and can become precursors of the formation and emission of significant amounts of carbon dioxide and methane into the atmosphere.

Simple Summary Seafloor biodiversity provides a key ecosystem service, as an efficient route for carbon to be removed from the atmosphere to become buried (long-term) in marine sediment. Protecting near intact ecosystems, particularly those that are hotspots of biodiversity, with high numbers of unique species (endemics), is increasingly being recognised as the best route to protect existing blue carbon. This study measured globally significant stocks of blue carbon held within both rocky (17.5 tonnes carbon km(-2)) and soft (4.1 t C km(-2)) substrata shallow (20 m) seafloor communities along the Antarctic Peninsula. Along the 7998 km of seasonally ice-free shoreline, 59% of known dive sites were classified as rocky and 12% as soft substratum. This gave estimates of 253k t C in animals and plants found at 20 m depth, with a potential sequestration of 4.5k t C year(-1). More carbon was stored in assemblages with greater functional groups. Of the Antarctic Peninsula shore, 54% is still permanently ice covered, and so blue carbon ecosystem services are expected to more than double with continued climate warming. As one of the few increasing negative feedbacks against climate change, protecting seafloor communities around the Antarctic is expected to help tackle both the biodiversity and climate crises. The importance of cold-water blue carbon as biological carbon pumps that sequester carbon into ocean sediments is now being realised. Most polar blue carbon research to date has focussed on deep water, yet the highest productivity is in the shallows. This study measured the functional biodiversity and carbon standing stock accumulated by shallow-water (<25 m) benthic assemblages on both hard and soft substrata on the Antarctic Peninsula (WAP, 67 degrees S). Soft substrata benthic assemblages (391 +/- 499 t C km(-2)) contained 60% less carbon than hard substrata benthic assemblages (648 +/- 909). In situ observations of substrata by SCUBA divers provided estimates of 59% hard (4700 km) and 12% soft (960 km) substrata on seasonally ice-free shores of the Antarctic Peninsula, giving an estimate of 253,000 t C at 20 m depth, with a sequestration potential of ~4500 t C year(-1). Currently, 54% of the shoreline is permanently ice covered and so climate-mediated ice loss along the Peninsula is predicted to more than double this carbon sink. The steep fjordic shorelines make these assemblages a globally important pathway to sequestration, acting as one of the few negative (mitigating) feedbacks to climate change. The proposed WAP marine protected area could safeguard this ecosystem service, helping to tackle the climate and biodiversity crises.