With Arctic amplification, hydrological conditions in Arctic permafrost regions are expected to change substantially, which can have a strong impact on carbon budgets. To date, detailed mechanisms remain highly uncertain due to the lack of continuous observational data. Considering the large carbon storage in these regions, understanding these processes becomes crucial for estimating the future trajectory of global climate change. This study presents findings from 8 years of continuous eddy-covariance measurements of carbon dioxide (CO2) and methane (CH4) fluxes over a wet tussock tundra ecosystem near Chersky in Northeast Siberia, comparing data between a site affected by a long-term drainage disturbance and an undisturbed control site. We observed a significant increasing trend in roughness lengths at both sites, indicating denser and/or taller vegetation; however, the increase at the drained site was more pronounced, highlighting the dominant impact of drainage on vegetation structure. These trends in aboveground biomass contributed to differences in gross primary production (GPP) between the two sites increasing over the years, continuously reducing the negative effect of the drainage disturbance on the sink strength for CO2. In addition, carbon turnover rates at the drained site were enhanced, with ecosystem respiration and GPP consistently higher compared to the control site. Because of the artificially lower water table depth (WTD), CH(4 )emissions at the drained site were almost halved. Furthermore, drainage altered the ecosystem's response to environmental controls. Compared to the control site, the drained site became slightly more sensitive to the global radiation (R-g), resulting in higher CO(2 )uptake under the same levels of R-g. Meanwhile, CH(4 )emissions at the drained site showed a higher correlation with deep soil temperatures. Overall, our findings from this WTD manipulation experiment show that changing hydrological conditions will significantly impact the Arctic ecosystem characteristics, carbon budgets, and ecosystem's response to environmental changes.

中高纬度地区是全球气候变化的敏感区域，近几十年来，该区年平均气温的增幅远高于全球平均增温幅度。中国东北地区地处中高纬度，是中国湿地的集中分布区之一，区域内湿地碳氮循过程对气候变化极为敏感。基于文献分析，归纳总结了温度升高对中国东北地区湿地温室气体通量的影响及其作用机制，梳理了湿地温室气体源汇功能的变化，在此基础上提出了当前研究中存在的问题并对未来研究进行了展望。总体来说，气温升高引起土壤温度升高、植物生长加快、微生物活性增强以及土壤理化性质的改变，从而影响湿地温室气体的吸收或排放。此外，气温升高可促使东北地区湿地由CH4的弱源向强源以及CO2由汇向源逐渐转变，但对N2O源汇变化的研究还存在较多不确定性。现有研究对东北地区湿地的覆盖还不够全面，缺少长时高频的监测以及多梯度、多因子交互作用的研究。未来应针对上述问题开展综合研究与分析，并进一步探究不同温室气体通量变化的相互影响机制。

Understanding the balance between methane (CH4) production (methanogenesis) and its oxidation is important for predicting carbon emissions from thermokarst lakes under global warming. However, the response of thermokarst lake methanogenesis and the anaerobic oxidation of methane (AOM) to warming, especially from Qinghai-Tibetan Plateau (QTP), is still not quantified. In this study, sediments were collected from 11 thermokarst lakes on the QTP. These lakes are surrounded with different vegetation types, including alpine desert (AD), alpine steppe (AS), alpine meadow (AM) and alpine swamp meadow (ASM). The results showed that methanogenesis and AOM rates exponentially increased with temperature, while the temperature sensitivity (Q10, average Q10 values of methanogenesis and AOM were 0.69-30 and 0.54-16.9 respectively) of methanogenesis were larger than AOM, but not significant, showing a similar temperature dependence of methanogenesis and AOM in thermokarst lake sediments. Thermokarst lake sediments in the ASM had higher methanogenesis and anaerobic oxidation potential, matching its higher NDVI and relative abundances of methanogens and SBM (syntrophic bacteria with methanogens). Although the thermokarst lake sediments AOM depleted 15 %-27.8 % of the total CH4 production, the AOM rate was lower than methanogenesis in thermokarst lake sediments, it did not offset increased CH4 production under anaerobic conditions. The increase in CH4 production in thermokarst lake sediments will likely lead to higher emissions within a warming world. These findings indicate that methanogenesis and AOM in thermokarst lake sediments are sensitive to climate change. Models should consider the Q10 values of methanogenesis and AOM and vegetation types when predicting carbon cycle in thermokarst lakes under global warming.

Greenhouse gases (GHGs) released from permafrost regions may have a positive feedback to climate change, but there is much uncertainty about additional warming from the permafrost carbon cycle. One of the main reasons for this uncertainty is that the observation data of large-scale GHG concentrations are sparse, especially for areas with rapid permafrost degradation. We selected the Mongolian Plateau as the study area. We first analyzed the active layer thickness and ground temperature changes using borehole observations. Based on ground observation data, we assessed the applicability of Greenhouse Gases Observing Satellite (GOSAT) carbon dioxide (CO2) and methane (CH4) datasets. Finally, we analyzed the temporal and spatial changes in near-surface CO2 and CH4 concentrations from 2010 to 2017 and their patterns in different permafrost regions. The results showed that the Mongolian permafrost has been experiencing rapid degradation. The annual average near-surface CO2 concentration increased gradually between 2.19 ppmv/yr and 2.38 ppmv/yr, whereas the near-surface CH4 concentration increased significantly from 7.76 ppbv/yr to 8.49 ppbv/yr. There were significant seasonal variations in near-surface CO2 and CH4 concentrations for continuous, discontinuous, sporadic, and isolated permafrost zones. The continuous and discontinuous permafrost zones had lower near-surface CO2 and CH4 concentrations in summer and autumn, whereas sporadic and isolated permafrost zones had higher near-surface CO2 and CH4 concentrations in winter and spring. Our results indicated that climate warming led to rapid permafrost degradation, and carbon-based GHG concentrations also increased rapidly in Mongolia. Although, GHG concentrations increased at rates similar to the global average and many factors can account for their changes, GHG concentration in the permafrost regions merits more attention in the future because the spatiotemporal distribution has indicated a different driving force for regional warming. (C) 2021 Elsevier B.V. All rights reserved.

Permafrost thawing may lead to the release of carbon and nitrogen in high-latitude regions of the Northern Hemisphere, mainly in the form of greenhouse gases. Our research aims to reveal the effects of permafrost thawing on CH4 and N2O emissions from peatlands in Xiaoxing'an Mountains, Northeast China. During four growing seasons (2011-2014), in situ CH4 and N2O emissions were monitored from peatland under permafrost no-thawing, mild-thawing, and severe-thawing conditions in the middle of the Xiaoxing'an Mountains by a static-chamber method. Average CH4 emissions in the severe-thawing site were 55-fold higher than those in the no-thawing site. The seasonal variation of CH4 emission became more aggravated with the intensification of permafrost thawing, in which the emission peaks became larger and the absorption decreased to zero. The increased CH4 emissions were caused by the expansion of the thawing layer and the subsequent increases in soil temperature, water table, and shifts of plant communities. However, N2O emissions did not change with thawing. Permafrost thawing increased CH4 emissions but did not impact N2O emissions in peatlands in the Xiaoxing'an Mountains. Increased CH4 emissions from peatlands in this region may amplify global warming.

Methane (CH4) is the second most significant driver of global warming, following carbon dioxide. However, the spatial-temporal variation of CH4 and its driving factors largely remain unclear. Here we selected the Northern Hemisphere as the study area. We used the data from the Total Column Carbon Observing Network (TCCON) to assess the accuracy of the Greenhouse Gases Observing Satellite (GOSAT) Proxy XCH4 (column-averaged dry air mixing ratio of CH4) data. We then analyzed the spatial-temporal distribution of XCH4 in the Northern Hemi-sphere, and further quantified the influencing factors using geographic detectors. The results showed that during 2009-2021, the annual mean XCH4 increased from 2009 (1775.19 ppb) to 2021 (1872.71 ppb), with an increasing rate of 7.50 ppb/year. The monthly average value was the lowest in May (1805.65 ppb) and the highest in September (1825.63 ppb). The XCH4 in the low-latitude region was higher than that in the high-latitudinal region. The geographic detector showed that anthropogenic activities were the main factors affecting the XCH4. Our results revealed the spatial-temporal patterns XCH4 and their driving factors in the Northern Hemisphere, and thus provided a scientific basis for the management of this greenhouse gas in the future.

With global warming, glaciers in the high mountains of China are retreating rapidly. However, few data have been reported on whether greenhouse gases from these glaciers are released into the atmosphere or absorbed by glacial meltwater. In this study, we collected meltwater and ice samples from Laohugou Glacier No. 12 in western China and measured CH4 and CO2 concentrations. Meltwater from the glacier terminus was continually sampled between 3 and 5 August 2020 to measure CH4 and CO2 concentrations. The results demonstrated that meltwater is a source of CH4 because the average saturations are over 100%. It could be concluded that CH4 in the atmosphere can be released by glacial meltwater. However, the CO2 saturations are various, and CO2 fluxes exhibit positive (released CO2) or negative (absorbed CO2) values because the water and atmospheric conditions are variable. More importantly, the CH4 and CO2 concentrations were higher in meltwater samples from the glacier terminus than in samples from the surface ice (including an ice core) and a surface stream. Although the meltwater effect from the upper part of the glacier cannot be excluded, we speculated that subglacial drainage systems with an anaerobic environment may represent the CH4 source, but it needs to be further investigated in the future. However, high mountain glaciers are currently ignored in global carbon budgets, and the increased melting of glaciers with global warming may accelerate the absorption of much more CO2 and lead to the release of CH4.

Arctic tundra ecosystems are rapidly changing due to the amplified effects of global warming within the northern high latitudes. Warming has the potential to increase the thawing of the permafrost and to change the landscape and its geochemical characteristics, as well as terrestrial biota. It is important to investigate microbial processes and community structures, since soil microorganisms play a significant role in decomposing soil organic carbon in the Arctic tundra. In addition, the feedback from tundra ecosystems to climate change, including the emission of greenhouse gases into the atmosphere, is substantially dependent on the compositional and functional changes in the soil microbiome. This article reviews the current state of knowledge of the soil microbiome and the two most abundant greenhouse gas (CO2 and CH4) emissions, and summarizes permafrost thaw-induced changes in the Arctic tundra. Furthermore, we discuss future directions in microbial ecological research coupled with its link to CO2 and CH4 emissions.

Taiga-tundra boundary ecosystems are affected by climate change. Methane (CH4) emissions in taiga-tundra boundary ecosystems have sparsely been evaluated from local to regional scales. We linked in situ CH4 fluxes (2009-2016) with vegetation cover, and scaled these findings to estimate CH4 emissions at a local scale (10x10km) using high-resolution satellite images in an ecosystem on permafrost (Indigirka lowland, north-eastern Siberia). We defined nine vegetation classes, containing 71 species, of which 16 were dominant. Distribution patterns were affected by microtopographic height, thaw depth and soil moisture. The Indigirka lowland was covered by willow-dominated dense shrubland and cotton-sedge-dominated wetlands with sparse larch forests. In situ CH4 emissions were high in wetlands. Lakes and rivers were CH4 sources, while forest floors were mostly neutral in terms of CH4 emission. Estimated local CH4 emissions (37mg m(-2) d(-1)) were higher than those reported in similar studies. Our results indicate that: (i) sedge and emergent wetland ecosystems act as hot spots for CH4 emissions, and (ii) sparse tree coverage does not regulate local CH4 emissions and balance. Thus, larch growth and distribution, which are expected to change with climate, do not contribute to decreasing local CH4 emissions.

Methane (CH4) is produced in many natural systems that are vulnerable to change under a warming climate, yet current CH4 budgets, as well as future shifts in CH4 emissions, have high uncertainties. Climate change has the potential to increase CH4 emissions from critical systems such as wetlands, marine and freshwater systems, permafrost, and methane hydrates, through shifts in temperature, hydrology, vegetation, landscape disturbance, and sea level rise. Increased CH4 emissions from these systems would in turn induce further climate change, resulting in a positive climate feedback. Here we synthesize biological, geochemical, and physically focused CH4 climate feedback literature, bringing together the key findings of these disciplines. We discuss environment-specific feedback processes, including the microbial, physical, and geochemical interlinkages and the timescales on which they operate, and present the current state of knowledge of CH4 climate feedbacks in the immediate and distant future. The important linkages between microbial activity and climate warming are discussed with the aim to better constrain the sensitivity of the CH4 cycle to future climate predictions. We determine that wetlands will form the majority of the CH4 climate feedback up to 2100. Beyond this timescale, CH4 emissions from marine and freshwater systems and permafrost environments could become more important. Significant CH4 emissions to the atmosphere from the dissociation of methane hydrates are not expected in the near future. Our key findings highlight the importance of quantifying whether CH4 consumption can counterbalance CH4 production under future climate scenarios. Plain Language Summary Methane is a powerful greenhouse gas, second only to carbon dioxide in its importance to climate change. Methane production in natural environments is controlled by factors that are themselves influenced by climate. Increased methane production can warm the Earth, which can in turn cause methane to be produced at a faster rate - this is called a positive climate feedback. Here we describe the most important natural environments for methane production that have the potential to produce a positive climate feedback. We discuss how these feedbacks may develop in the coming centuries under predicted climate warming using a cross-disciplinary approach. We emphasize the importance of considering methane dynamics at all scales, especially its production and consumption and the role microorganisms play in both these processes, to our understanding of current and future global methane emissions. Marrying large-scale geophysical studies with site-scale biogeochemical and microbial studies will be key to this.