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Suaeda salsa acts as a natural barrier between land and sea in estuarine wetlands while also serving as a significant source of carbon storage. Understanding the synergistic relationship between the spatial distribution of Suaeda salsa habitat suitability and its carbon storage capabilities is essential for guiding ecological restoration and bolstering the carbon sequestration potential of wetlands. Drawing on field survey data from the Liaohe River Estuary wetlands collected in 2021 and 2022, we applied the Maxent model to delineate the spatial distribution of Suaeda salsa habitat suitability. The findings indicate that the principal environmental determinants for the Suaeda salsa community are elevation, soil phosphorus, and sand and soil salt content. Habitats can be divided from into four classes with increasing suitability index: I, II, III, and IV. As the most favorable habitat, class IV spanned 33.07 km 2 and constituted 22.37 % of the area. By integrating remote sensing and ground survey data, a carbon storage evaluation model for Suaeda salsa was developed. This model revealed that the carbon storage within the Liaohe River Estuary reached 8238.18 and 16,194.08 tons in 2021 and 2022, respectively. Finally, the spatial overlay analysis of habitat suitability distribution and carbon storage revealed that an increase in habitat suitability led to an increase in carbon storage in Suaeda salsa, which was also influenced by the surrounding land use types. This work demonstrates a significant positive correlation between habitat suitability and carbon sequestration capacity. In the future, we suggest that ecological restoration projects in the Liaohe Estuary region focus on areas with higher habitat suitability. This study supports the sustainable management of the Suaeda salsa community and provides a theoretical basis for enhancing the carbon sequestration capacity of estuarine wetlands., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study used dual stable isotopes to examine nitrate sources and geographical distribution in the Liao River Basin (LRB), one of China's seven major river basins. During a normal hydrological season in April 2021, water samples were taken from the main streams of the Liao River (MLR), Shuangtaizi River (STR), Hun River (HR), Taizi River (TZR), and Daliao River (DLR). Monitoring results indicated that 93% of the water samples had a total nitrogen level exceeding the Class IV limit (1.5 mg/L) of the 'Environmental Quality Standards (EQS) for surface water', indicating a serious nitrogen pollution status. 71.3% of the total nitrogen on average was in the form of nitrate. The scatterplots of δD-H 2 O and δ 18 O-H 2 O showed that water in TZR and DLR were mainly affected by precipitation, while MLR, STR and HR were additionally impacted by evaporation and groundwater. The overall δ 15 N and δ 18 O of NO 3 - varied from 7.7‰ to 17.9‰ and 0.6‰-11.2‰, respectively. The correlations between δ 15 N-NO 3 - and δ 18 O-NO 3 - , along with attribution results from the Bayesian isotopic mixing model, indicated a predominant role of manure/sewage (MS) pollution in affecting river nitrate, accounting for 78% of total nitrate in MLR and 72% in DLR. A positive correlation between δ 15 N-NO 3 - and δ 18 O-NO 3 - in MLR indicated the occurrence of denitrification process. Overall, attribution results showed that the primary nitrate sources varied in different river systems within such a large basin, mainly due to spatially varied land use and human activities. Tailored nitrogen management strategies should be implemented to address the main anthropogenic pressures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Ensuring agricultural security and preserving the health of wetland ecosystems are crucial concerns facing northeast China. However, the adverse effects of environmental pollution, especially nitrogen (N), caused by prolonged agricultural development on the health of marsh wetlands cannot be systematically recognized. To address this issue, an 18-year trial with four different levels of N application was carried out in a typical area of the Northeast region: 0, 6, 12, and 24 gN·m -2 ·a -1 (referred to as CK, N6, N12, and N24, respectively) to investigate changes in wetland ecological functioning. The results showed that long-term N input significantly enhanced soil N availability. High-level of N addition (N24) significantly reduced soil bacterial richness in October, while fungal diversity was significantly higher in June than in October for both control and N6 treatments. The main environmental factors affecting microorganisms in June were TN, NH 4 + , and EC, while bacterial and fungal communities were influenced by TN and Leaf Area Index (LAI), respectively, in October. It was found that the AN16S gene was significantly higher in June than in October, indicating that summer is the critical time for N removal in the wetland. N addition significantly reduced the abundance of the NIFH gene and decreased the N fixation potential of the wetland. In June, low and medium levels of N inputs promoted denitrification processes in the wetland and elevated the wetland N 2 O emission potential. The abundance of NARG, NIRK, and NOSZ genes decreased significantly in October compared to June, indicating a decrease in the wetland N 2 O emission potential. Additionally, it was observed that soil methanotrophs were positively affected by NH 4 + and TN in October, thereby reducing the wetland CH 4 emission potential. Our research provides a systematic understanding of the impact of agricultural N pollution on marsh wetlands, which can inform strategies to protect wetland health., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Dissolved organic carbon (DOC), the labile fraction of organic carbon, is a predominant substrate for microbes. Therefore, the turnover of DOC dominates microbial respiration in soils. We compiled a global dataset (1096 data points) of the turnover rates of DOC in 0-30 cm soil profiles and integrated the data with a machine learning algorithm to develop a global map of DOC turnover rate in global topsoil. The global DOC turnover rate in 0-30 cm soil was averaged as 0.0087 day -1 , with a considerable variation among biomes. The fastest DOC turnover rate was found in tropical forests (0.0175 day -1 ) and the lowest in tundra (0.0036 day -1 ), exhibiting a declining trend from low to high latitudes. The DOC turnover rate is primarily controlled by edaphic and climate factors, as confirmed by the analyses with the structural equation model and the Mental's test. With a machine learning algorithm, we produced global maps of DOC turnover rate at a monthly scale, which were further combined with a global dataset of DOC density to produce monthly maps of carbon mineralization from DOC turnover in topsoil. The annual carbon release from DOC was estimated as 27.98 Pg C year -1 from topsoil across the globe, with the largest contribution from forest biomes, followed by pasture and grassland. Tundra released the least carbon from DOC due to its low turnover rate suppressed by low temperatures. The biome- and global-scale information of DOC turnover rate and carbon release from DOC provide a benchmark for ecosystem models to better project soil carbon dynamics and their contributions to global carbon cycling in the changing environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing interests regarding the publication of this work., (Copyright © 2023. Published by Elsevier B.V.)

Phosphorus is widely recognized as a nutrient that restricts growth and is the primary contributor to eutrophication in 80 % of water bodies. Consequently, the Chinese government has consistently prioritized monitoring and controlling total phosphorus (TP) levels. The remote estimation of TP in lakes and reservoirs at a national scale is a challenging task due to TP being a non-optically active parameter. Currently, there is a lack of developed TP inversion models specifically designed for lakes and reservoirs in China. For solving this problem, a novel two-line classification method drawn on scatter plots based on the natural logarithm of TP (Ln(TP)) and B33/B9 was proposed and used to classify 1211 measured samples obtained from field cruises in 105 lakes and reservoirs across China from 2012 to 2022 into three categories, Class 1, Class 2, and Class 3. Results demonstrate that the proposed classification method has the ability to enhance the correlation between Ln(TP) and 43 basic potential single band and band combinations. Specifically, the correlation range improved from (-0.31,0.15) to (-0.77,0.24) in Class 1, (-0.81, 0.36) in Class 2, and (-0.74, 0.52) in Class 3. Additionally, the classification method also improved the correlation range between Ln(TP) and 820 band ratios, from (-0.32, 0.32) to (-0.83, 0.82) in Class 1, (-0.86, 0.86) in Class 2, and (-0.86, 0.86) in Class 3. These datasets were subsequently utilized as input for eXtreme Gradient Boosting (XGBoost) models. Finally, well performing XGBoost models in Class 1 (R 2  = 0.76, RMSE = 0.3, MAPE = 12 %), Class 2 (R 2  = 0.84, RMSE = 0.49, MAPE = 38 %), and Class 3 (R 2  = 0.74, RMSE = 0.46, MAPE = 14 %) were used to map TP of 563 large lakes and reservoirs (≥20 km 2 ) across China using MODIS images from 2005, 2010, 2015, and 2020. This study presents a novel approach for estimating non-optically active parameters through remote sensing on a national scale., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Chlorophyll-a (Chla) in inland waters is one of the most significant optical parameters of aquatic ecosystem assessment, and long-term and daily Chla concentration monitoring has the potential to facilitate in early warning of algal blooms. MOD09 products have multiple observation advantages (higher temporal, spatial resolution and signal-to-noise ratio), and play an extremely important role in the remote sensing of water color. For developing a high accuracy machine learning model of remotely estimating Chla concentration in inland waters based on MOD09 products, this study proposed an assumption that the accuracy of Chla concentration retrieval will be improved after classifying water bodies into three groups by suspended particulate matter (SPM) concentration. A total of 10 commonly used machine learning models were compared and evaluated in this study, including random forest regressor (RFR), deep neural networks (DNN), extreme gradient boosting (XGBoost), and convolutional neural network (CNN). Altogether, 41 basic bands and 820 band ratios between the 41 bands were filtered by measuring their correlation with Ln(Chla) and several bands brought into different machine learning models. Results demonstrated that the construction of Chla concentration remote estimation model based on SPM classification could significantly improve the correlation between Ln(Chla) and 41 basic spectral band combinations, the correlation between Ln(Chla) and 820 band ratios, and the model verification R 2 from 0.41 to 0.83. Furthermore, B3, B20, and B32 were finally selected based on correlation with SPM to classify SPM and the classification accuracy could reach 0.9. Finally, we concluded that RFR model performed best via comparing the R 2 , RMSE, and MAPE. By comparing the relative contribution of input bands in different groups, B3 contributed most to three groups. The model constructed in this study has promising prospects for promotion and application in other inland waters, and could provide systematic research reference for subsequent research., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The carbon (C) balance of permafrost peatlands in autumn and winter, which affects the annual C budget estimation, has become a hotspot of studies on peatlands C cycle. This study combined the static chamber method, in situ soil profile measurements, and incubation experiments to investigate release and storage of C during autumn and early winter in a permafrost peatland in the Da Xing'an Mountains, Northeast China. Our results showed that the peak values of CH 4 fluxes (30 August 2016) lagged behind those of CO 2 fluxes (24 July 2016). At the onset of soil freezing, CH 4 fluxes slightly increased, while CO 2 fluxes decreased. During soil freezing in autumn, gases were found to be mainly stored in the soil as dissolved CH 4 and CO 2 and dissolved C concentrations (CH 4 , CO 2 , and DOC (dissolved organic carbon)) increased with depth. DOC concentrations were closely related to dissolved C gases, implying that the stored dissolved C gases might be derived from DOC decomposition. The CO 2 : CH 4 ratio decreased sharply from the freezing of the surface layer to the total freezing of the soil, indicating larger CH 4 storage in totally frozen soil. The incubation experiments also showed larger CH 4 storage in the frozen soils and the stored C gases could influence the assessment of C emissions during thawing. These findings have important implications for clarifying the gas storage of permafrost peatland in autumn and early winter. The results may also clarify the key link of C emissions between the growing season and the nongrowing season., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Soil microbial responses to environmental stress remain a critical question in microbial ecology. The content of cyclopropane fatty acid (CFA) in cytomembrane has been widely used to evaluate environmental stress on microorganisms. Here, we used CFA to investigate the ecological suitability of microbial communities and found a stimulating impact of CFA on microbial activities during wetland reclamation in Sanjiang Plain, Northeastern China. The seasonality of environmental stress resulted in the fluctuation of CFA content in the soil, which suppressed microbial activities due to nutrient loss upon wetland reclamation. After land conversion, the aggravation of temperature stress to microbes increased the CFA content by 5 % (autumn) to 163 % (winter), which led to the suppression of microbial activities by 7 %-47 %. By contrast, the warmer soil temperature and permeability decreased the CFA content by 3 % to 41 % and consequently aggravated the microbial reduction by 15 %-72 % in spring and summer. Complex microbial communities of 1300 CFA-produced species were identified using a sequencing approach, suggesting that soil nutrients dominated the differentiation in these microbial community structures. Further analysis with structural equation modeling highlighted the important function of CFA content to environmental stress and the stimulating influence of CFA induced by environmental stress on microbial activities. Our study shows the biological mechanisms of seasonal CFA content for microbial adaption to environmental stress under wetland reclamation. It advances our knowledge of microbial physiology affecting soil element cycling caused by anthropogenic activities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Mineral protection can slow the effect of warming on the mineralization of organic carbon (OC) in permafrost wetlands, which has an important impact on the dynamics of soil OC. However, the response mechanisms of wetland mineral soil to warming in permafrost areas are unclear. In this study, the soil of the southern edge of the Eurasian permafrost area was selected, and bulk and heavy fraction (HF) soil was subjected to indoor warming incubation experiments using physical fractionation. The results showed that the HF accounted for 51.25 % of the total OC mineralization in the bulk soil, and the δ 13 C value of the CO 2 that was emitted in the HF soil was higher than that of the bulk soil. This indicates the potential availability of mineral soil and that the mineralized OC in the HF was the more stable component. Additionally, the mineralization of the mineral subsoil after warming by 10 °C was only about half of the increase in the organic topsoil, and the temperature sensitivity was significantly negatively correlated with the Fe/Al oxides to OC ratio. The results indicate that under conditions of permafrost degradation, the physical protection of mineral soil at high latitudes is essential for the stability of OC, which may slow the trend of permafrost wetlands becoming carbon sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

As an elemental carbon (C) and nitrogen (N) pool in the world, peatlands are very sensitive to environmental changes. Under global warming, the increase in available N affects the dynamic changes of plant community structure and nutrients in a permafrost peatland. This study was based on a long-term in situ N addition experiment that had been conducted for 9 years. It utilized the peatland in the permafrost area of Great Hing'an Mountain as the research object to analyze the effects of N addition on the growth characteristics, community structure, and nutrient dynamics of peatland plants. The N inputs were N1: 6 g N m -2 ·year -1 , N2: 12 g N m -2 ·year -1 and N3: 24 g N m -2 ·year -1 , respectively. Our results showed that the adding N can affect the plant community structure of peatland by affecting the plant growth characteristics. The diversity and richness of plant species in the peatland decreased as the concentration of added N increased. The long-term N addition can reduce the N limitation of plants to some extent. Still, it could further aggravate their phosphorus (P) limitation, resulting in the joint limitation of N and P or the complete limitation by P. The N resorption efficiency decreased with the increase of N addition level. The P resorption efficiency of different plants had varied responses to the changes in the N nutrient environment. Our study clarified the impact of long-term N addition on the plant community structure and nutrient dynamics of peatland in a permafrost area and provided an important theoretical basis to accurately evaluate the carbon and nitrogen balance of peatland in a permafrost area owing to future climate change., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Peatlands in northeast China are experiencing severe climate warming. Most studies on peatlands focus on the responses of CH 4 dynamics to temperature. However, they rarely consider the synchronous changes in the composition of plant communities caused by the expansion of vascular plants. In this study, an experiment combined warming with the manipulation of plants to examine the concentrations of CH 4 porewater and its fluxes in the mesocosm. We found that warming increased the concentration of CH 4 and its fluxes relative to the control treatments, and it was strongly modulated by plant richness and functional types. The average CH 4 fluxes in the warming and non-warming mesocosms varied from 72.10 to 119.44 and 97.95 to 194.43 mg m -2  h -1 , respectively. Plant species richness significantly increased CH 4 flux at the warming level of 3.2 °C (P < 0.01). The presence of vascular plants, such as Carex globularis and Vaccinium uliginosum, significantly increased the CH 4 fluxes after warming had occurred. Our results suggest that the distinct response of CH 4 to richness and species primarily stemmed from the direct or indirect effects of plant biomass and functional characteristics. Therefore, more consideration should be given to the diversity changes caused by vascular plant expansion when estimating CH 4 flux in boreal peatland, especially in the context of future climate warming., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Mitigating environmental pollution and sustaining grain production have been foundational issues in sustainable development, however, ascertaining the optimal balance remains poorly investigated. This study used the Soil and Water Assessment Tool (SWAT) model to simulate crop growth and nitrogen loss, established the mapping relationship between nitrogen input to yield and water quality, and proposed a general method to determine a nitrogen application strategy for high yield and low pollution at a basin scale. Lake Xiaoxingkai basin, which is the primary maize producing area in China as well as an internationally important wetland distribution area, was used as a case study. First, we designed application scenarios for 10 base fertilizers (B1-B10) and 10 topdressing fertilizers (T1-T10) and evaluated their combined effects of maize growth to identify the critical nitrogen fertilizer rates determined under fixed and dynamic base/topdressing ratios. Then, the critical base and topdressing fertilizer rates were determined. Based on the mapping relationship between nitrogen fertilizer rate and nitrogen loss, we then revealed water quality at the basin outlet under the critical base and topdressing fertilizer rates. Finally, we proposed alternative nitrogen application strategies for high yield and low pollution while considering the different preferences of decision-makers for the economy, agriculture, and environment. We found that adjusting the ratio of base to topdressing fertilizer may create a win-win situation for agriculture and the environment, which will provide a scientific basis for sustainable development., Competing Interests: Declaration of competing interest We declared that there have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Little is known about the influence of conversion of wetlands to farmlands on concentrations and distribution of elements other than those most commonly studied, partly because of the lack of stratification in wetland soils. In this study, in the Sanjiang Plain in northeastern China, we determined the concentrations of 63 elements along soil profiles at three depths: 0-20 cm, 20-40 cm, and below the depth to which farmers would plow, at 40-60 cm, under four land uses: natural wetland, drained wetland, wetland converted to soybean field and subsequently to rice paddy field. Based on our previous work, we expected that changes in organic matter content would be an important factor affecting element concentrations, but that changes in land uses also led to decoupling of the influence of organic matter on elements. This would lead to other factors, such as changes in redox conditions, changes in hydrology and mixing of soils due to plowing, becoming more important factors affecting element distributions. Our study confirmed these expectations. Changes in organic matter content directly or indirectly affected many elements, explaining 67% of variation. Arsenic, cobalt, iron and nickel concentrations were dramatically higher and sulfur concentrations lower when wetland was converted to paddy field. Co and Ni were identified as potential chemical indicators of wetland conversion. Our research is the first to use multi-element fingerprinting to study effects of conversion of wetlands to croplands in China and showed that this relatively simple approach highlights the complexity of the many interacting factors in reclamation of wetland soils for agricultural uses., Competing Interests: Declaration of competing interest All authors listed below have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version. This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue. The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript. This statement is approved by all the authors to indicate agreement that the above information is true and correct., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Permafrost play an important role in regulating global climate system. We analyzed the gross primary productivity (GPP), net primary productivity (NPP), and evapotranspiration (ET) derived from MODIS and three earth system models participated in the Coupled Model Inter-comparison Project Phase 6 (CMIP6) in the Asian permafrost region. The water use efficiency (WUE) was further computed. The simulated GPP, NPP, and ET show slightly increasing trends during historical period (1900-2014) and strong increasing trends in projection period (2015-2100), and projected impacts of climate change on all variables are greater under high-emission scenarios than low-emission scenarios. Further analysis revealed higher increases in GPP and NPP than that of ET, indicating that vegetation carbon sequestration governs the growing WUE under historical and projected periods in this region. The GPP, NPP and ET showed higher changing rates in western, central and southeast areas of this region, and WUE (WUE GPP , and WUE NPP ) shows the similar spatial pattern. Compared to MODIS-derived GPP, NPP, and ET during 2000-2014, Earth system models yield the best estimates for NPP, while slight underestimations for GPP and ET, and thus slight overestimations for WUE GPP and WUE NPP . This study highlights the predominant role of vegetation activity in regulating regional WUE in Asian permafrost region under future climate change. Vegetation domination of the growing water use efficiency implies that the permafrost region may continue acting efficiently in sequestrating atmospheric carbon in terms of water consumption throughout the 21st century., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Eurasian permafrost serves as an important nitrogen source for linked aquatic and oceanic ecosystems. To fill in the data gaps in the southern margin of the Eurasian permafrost, nitrogen dynamics in the two rivers that drain the permafrost in the Great Xing'an Mountains of northeast China were investigated during the 2012-2015 growing seasons. The mean concentration of total dissolved nitrogen (TDN) in the two catchments was 0.63 mg L -1 , which is generally higher than other permafrost catchments around the Arctic Ocean. The dissolved organic nitrogen (DON) constituted the majority of TDN, and the mean DON:TDN ratio was as high as 0.84. The seasonal flood patterns broadly influenced the concentrations and annual loads of DON, as well as the dissolved organic carbon (DOC):DON ratios in the two rivers. River discharge was positively related to DON concentration during growing seasons, while the concentrations of dissolved inorganic nitrogen (DIN), namely ammonium and nitrate, demonstrated no relationship with discharge. The estimated annual TDN yield, 190 kg km -2  yr -1 on average, was much higher than in the large Arctic rivers that drain permafrost. This yield accounts for 42.7% of the total atmospheric nitrogen deposition in the study area, which indicates a great potential for dissolved nitrogen export from the permafrost area in the Great Xing'an Mountains., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Nitrogen (N) availability affects litter decomposition and nutrient dynamics, especially in N-limited ecosystems. We investigated the response of litter decomposition to N additions in Eriophorum vaginatum and Vaccinium uliginosum peatlands. These two species dominate peatlands in Northeast China. In 2012, mesh bags containing senesced leaf litter of Eriophorum vaginatum and Vaccinium uliginosum were placed in N addition plots and sprayed monthly for two years with NH 4 NO 3 solution at dose rates of 0, 6, 12, and 24gNm -2 year -1 (CK, N1, N2 and N3, respectively). Mass loss, N and phosphorus (P) content, and enzymatic activity were measured over time as litter decomposed. In the control plots, V. uliginosum litter decomposed faster than E. vaginatum litter. N1, N2, and N3 treatments increased the mass losses of V. uliginosum litter by 6%, 9%, and 4% respectively, when compared with control. No significant influence of N additions was found on the decomposition of E. vaginatum litter. However, N and P content in E. vaginatum litter and V. uliginosum litter significantly increased with N additions. Moreover, N additions significantly promoted invertase and β-glucosidase activity in E. vaginatum and V. uliginosum litter. However, only in V. uliginosum litter was polyphenol oxidase activity significantly enhanced. Our results showed that initial litter quality and polyphenol oxidase activity influence the response of plant litter to N additions in peatland ecosystems. Increased N availability may change peatland soil N and P cycling by enhancing N and P immobilization during litter decomposition., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In boreal peatlands, litter decomposition plays an important role in modulating ecosystem carbon (C) cycling and nutrient turnover. However, how climate warming and plant functional group interact to affect litter decomposition is still unclear in these ecosystems. Here, we collected fresh litters of six plant functional groups (nitrogen (N)-fixing species, deciduous tree, deciduous shrub, evergreen shrub, graminoid, and Sphagnum moss) from a boreal peatland located in northeast China. A laboratory incubation experiment was used to determine the effect of temperature (10 °C vs. 20 °C) on microbial respiration and mass loss during decomposition. Among the six functional groups, the litters of N-fixing species and deciduous shrub, followed by deciduous tree, generally had the greatest mass losses and microbial respiration rates, whereas the Sphagnum moss decomposed with the slowest rate at both incubation temperatures. Increasing incubation temperature from 10 °C to 20 °C, microbial respiration rate and mass loss increased slightly for Sphagnum moss litters (25% and 19%, respectively), but increased dramatically for vascular plant litters (84-135% and 49-85%, respectively). For litters from vascular plants, both decomposition rate and temperature sensitivity showed a tight linear correlation with the initial C:N and C:phosphorus ratios. Considering that climate warming will cause increased dominance of woody plant species coupled with decreased cover by Sphagnum mosses, this study provides clear evidence that climate warming and the associated changes to vegetation community composition can synergistically accelerate plant litter decomposition in boreal peatlands., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Diurnal freeze-thaw cycles (FTCs) occur in the spring and autumn in boreal wetlands as soil temperatures rise above freezing during the day and fall below freezing at night. A surge in methane emissions from these systems is frequently documented during spring FTCs, accounting for a large portion of annual emissions. In boreal wetlands, methane is produced as a result of syntrophic microbial processes, mediated by a consortium of fermenting bacteria and methanogenic archaea. Further research is needed to determine whether FTCs enhance microbial metabolism related to methane production through the cryogenic decomposition of soil organic matter. Previous studies observed large methane emissions during the spring thawed period in the Sanjiang seasonal frozen marsh of Northeast China. To investigate how FTCs impact the soil microbial community and methanogen abundance and activity, we collected soil cores from the Sanjiang marsh during the FTCs of autumn 2014 and spring 2015. Methanogens were investigated based on expression level of the methyl coenzyme reductase (mcrA) gene, and soil bacterial and archaeal community structures were assessed by 16S rRNA gene sequencing. The results show that a decrease in bacteria and methanogens followed autumns FTCs, whereas an increase in bacteria and methanogens was observed following spring FTCs. The bacterial community structure, including Firmicutes and certain Deltaproteobacteria, was changed following autumn FTCs. Temperature and substrate were the primary factors regulating the abundance and composition of the microbial communities during autumn FTCs, whereas no factors significantly contributing to spring FTCs were identified. Acetoclastic methanogens from order Methanosarcinales were the dominant group at the beginning and end of both the autumn and spring FTCs. Active methanogens were significantly more abundant during the diurnal thawed period, indicating that the increasing number of FTCs predicted to occur with global climate change could potentially promote CH 4 emissions in seasonal frozen marshes., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Climate warming is expected to increasingly influence boreal peatlands and alter their greenhouse gases emissions. However, the effects of warming on N 2 O fluxes and the N 2 O budgets were ignored in boreal peatlands. Therefore, in a boreal peatland of permafrost zone in Northeast China, a simulated warming experiment was conducted to investigate the effects of warming on N 2 O fluxes in Betula. Fruticosa community (B. Fruticosa) and Ledum. palustre community (L. palustre) during the growing seasons from 2013 to 2015. Results showed that warming treatment increased air temperature at 1.5m aboveground and soil temperature at 5cm depth by 0.6°C and 2°C, respectively. The average seasonal N 2 O fluxes ranged from 6.62 to 9.34μgm -2 h -1 in the warming plot and ranged from 0.41 to 4.55μgm -2 h -1 in the control plots. Warming treatment increased N 2 O fluxes by 147% and transformed the boreal peatlands from a N 2 O sink to a source. The primary driving factors for N 2 O fluxes were soil temperature and active layer depth, whereas soil moisture showed a weak correlation with N 2 O fluxes. The results indicated that warming promoted N 2 O fluxes by increasing soil temperature and active layer depth in a boreal peatland of permafrost zone in Northeast China. Moreover, elevated N 2 O fluxes persisted in this region will potentially drive a noncarbon feedback to ongoing climate change., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Rapid and periodic assessment of the impact of land cover changes on ecosystem services at regional levels is essential to understanding services and sustainability of ecosystems. This study focused on quantifying and assessing changes of multiple ecosystem services in the Sanjiang Plain of China as a result of land cover changes over the period of 1992-2012. This region is important for its large area of natural wetlands and intensive agriculture. The ecosystem services that were assessed for this region included its regulating services (water yield and ecosystem carbon stocks), supporting services (suitable waterbird habitats), and provisioning services (food production), and the approach to the assessment was composed of the surface energy balance algorithms for land (SEBAL), soil survey re-sampling method and an empirical waterbird habitat suitability model. This large scale and integrated investigation represents the first systematic evaluation on the status of ecosystem carbon stocks in the Sanjiang Plain in addition to the development of an effective model for analysis of waterbird habitat suitability with the use of both remote sensing and geographic information systems (GIS). More importantly, the result from this study has confirmed trade-offs between ecosystem services and negative consequences to environment in this region. The trade-offs were typically manifested by increased water yield and significantly grown food production, which is in contrast with significant losses in ecosystem carbon stocks (-14%) and suitable waterbird habitats (-23%) mainly due to the conversion of land cover from wetland to farmland. This finding implies that land use planning and policy making for this economically important region should take ecosystem service losses into account in order to preserve its natural ecosystems in the best interest of society., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The carbon (C) pool of permafrost peatland is very important for the global C cycle. Little is known about how permafrost thaw could influence C emissions in the Great Hing'an Mountains of China. Through aerobic and anaerobic incubation experiments, we studied the effects of permafrost thaw on CH4 and CO2 emissions. The rates of CH4 and CO2 emissions were measured at -10, 0 and 10°C. Although there were still C emissions below 0°C, rates of CH4 and CO2 emissions significantly increased with permafrost thaw under aerobic and anaerobic conditions. The C release under aerobic conditions was greater than under anaerobic conditions, suggesting that permafrost thaw and resulting soil environment change should be important influences on C emissions. However, CH4 stored in permafrost soils could affect accurate estimation of CH4 emissions from microbial degradation. Calculated Q10 values in the permafrost soils were significantly higher than values in active-layer soils under aerobic conditions. Our results highlight that permafrost soils have greater potential decomposability than soils of the active layer, and such carbon decomposition would be more responsive to the aerobic environment., (© 2013 Elsevier B.V. All rights reserved.)

In this paper, CH(4) flux was measured from Nov. 2002 to Oct. 2005, to estimate CH(4) emissions in winter and during freeze-thaw period, and interannual variation in CH(4) emissions in freshwater marsh in northeast China. The results showed that there was an obvious CH(4) emission (0.1-2.3 mg m(-2) h(-1)) in the freshwater marsh in winter. Flux of CH(4) in winter (November to March the next year) was about 3.8%, 5.5%, and 2.2% of the whole year in 2003, 2004, and 2005, respectively. Emission of CH(4) significantly increased during the freeze-thaw period (April-June), and was about 30.8%, 20.9%, and 20.6% of the whole year in 2003, 2004, and 2005, respectively. Standing water depth greatly governed interannual variation of CH(4) emissions from marshes during the thaw-freeze period. Interannual variation of CH(4) emissions was significant during the growing season (p<0.05). Standing water depth during April to June was a primary factor, which affected the interannual variation of CH(4) flux during the growing season. Precipitation during the preceding non-growing season affected CH(4) emission indirectly via standing water depth.