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Approximately one-third of northern peatlands are within permafrost regions. Soil organic matter (SOM) and plant root biomass in permafrost peatlands are vulnerable to future global warming. However, previous studies have primarily focused on the response of SOM mineralization to increases in temperature without analysing the potential interaction effects of increased plant root biomass. This study investigated the influence of temperature and root additions on soil carbon and nitrogen mineralization as well as the mechanisms driving mineralization in a high latitude permafrost peatland in the Da Xing'an Mountains, Northeast China. We investigated changes in shallow soil (0–15 cm) and deep soil (15–30 cm) carbon mineralization, available N contents, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and enzyme activities in response to increasing temperature and Eriophorum vaginatum root additions by using an incubation experiment. Our results indicate that elevated temperature significantly increased soil carbon mineralization. The Q 10 values of the carbon mineralization rates in the shallow soil and deep soil were 3.95 and 2.91, respectively. In contrast, the soil MBC and DOC decreased significantly, confirming that labile carbon is the main driving force of microbial mineralization activities under warming conditions. Elevated temperature significantly increased the shallow soil net N mineralization rates and increased the net nitrification rates in both soil layers. At high temperatures, ammonification rates increased in the shallow soil but decreased in the deep soil. The increase in the incubation temperature resulted in significantly increased shallow soil β-glucosidase activity and decreased invertase activity. This suggests the increased production of complex substrate enzymes, and decreased production of simple substrate-acquiring enzymes. The root additions significantly increased the soil C mineralization and stimulated the secretion of invertase by soil microorganisms. These findings indicate that future climate warming in the northern high latitude will significantly stimulate soil carbon and nitrogen mineralization in permafrost peatlands. Furthermore, increases in plant roots will enhance C accumulation and may even enhance the response of soil C mineralization to temperature, significantly impact the soil C balance in high latitude permafrost peatlands. [ABSTRACT FROM AUTHOR]

• The decomposition of E. vaginatum litter is faster than that of Sphagnum. • Warming could promote decomposition of E. vaginatum and Sphagnum litter. • N addition promoted the decomposition of Sphagnum (low N) and vascular litter. • High N concentration inhibited the decomposition of Sphagnum litter. • Microorganisms regulated warming and N addition impacts on litter decomposition. As one kind of the most important carbon (C) sink in the world, peatlands are sensitive to climate change. The decomposition of litter plays an important role in C fixation and nutrient utilization in peatlands. To reveal the mechanism of response of the litter decomposition to climate warming and the addition of nitrogen (N) in permafrost peatlands, we selected two typical plants, Eriophorum vaginatum and Sphagnum palustre , in the permafrost peatland of Da Xing'anling Mountains, China, as the research objects and conducted a 54-day litter decomposition experiment at 10 ℃ and 20 ℃. Three N addition treatments (CK: 0 mg N g−1, N1: 2.5 mg N g−1, and N2: 5 mg N g−1) were established. Our results showed that the E. vaginatum litter decomposed more quickly than that of Sphagnum , and an increase in temperature significantly promoted the litter decomposition and CO 2 emission of E. vaginatum and Sphagnum. The addition of N promoted the decomposition of E. vaginatum litter, whereas the decomposition of Sphagnum litter was promoted by the N1 treatment but was inhibited by the N2 treatment. The enzyme activity in both types of litter was inhibited with the increase in temperature. The abundances of bacteria and fungi positively correlated with the decomposition constant and mean CO 2 release rate by E. vaginatum and Sphagnum litter, indicating that the effects of temperature and N addition on the decomposition of plant litter were primarily regulated by microorganisms. This study provides a theoretical basis to understand and predict the effects of global climate change on the decomposition of plant litter in boreal peatlands. [ABSTRACT FROM AUTHOR]

• The decomposition of E. vaginatum litter is faster than that of Sphagnum. • Warming could promote decomposition of E. vaginatum and Sphagnum litter. • N addition promoted the decomposition of Sphagnum (low N) and vascular litter. • High N concentration inhibited the decomposition of Sphagnum litter. • Microorganisms regulated warming and N addition impacts on litter decomposition. As one kind of the most important carbon (C) sink in the world, peatlands are sensitive to climate change. The decomposition of litter plays an important role in C fixation and nutrient utilization in peatlands. To reveal the mechanism of response of the litter decomposition to climate warming and the addition of nitrogen (N) in permafrost peatlands, we selected two typical plants, Eriophorum vaginatum and Sphagnum palustre , in the permafrost peatland of Da Xing'anling Mountains, China, as the research objects and conducted a 54-day litter decomposition experiment at 10 ℃ and 20 ℃. Three N addition treatments (CK: 0 mg N g−1, N1: 2.5 mg N g−1, and N2: 5 mg N g−1) were established. Our results showed that the E. vaginatum litter decomposed more quickly than that of Sphagnum , and an increase in temperature significantly promoted the litter decomposition and CO 2 emission of E. vaginatum and Sphagnum. The addition of N promoted the decomposition of E. vaginatum litter, whereas the decomposition of Sphagnum litter was promoted by the N1 treatment but was inhibited by the N2 treatment. The enzyme activity in both types of litter was inhibited with the increase in temperature. The abundances of bacteria and fungi positively correlated with the decomposition constant and mean CO 2 release rate by E. vaginatum and Sphagnum litter, indicating that the effects of temperature and N addition on the decomposition of plant litter were primarily regulated by microorganisms. This study provides a theoretical basis to understand and predict the effects of global climate change on the decomposition of plant litter in boreal peatlands. [ABSTRACT FROM AUTHOR]

• Rising temperature accelerated the mineralization of SOC in permafrost peatlands. • Q 10 of SOC mineralization ranged from 2.24 to 4.22 among 7 permafrost peatlands. • SOC mineralization positively correlated with soil DOC, NH 4 +-N, NO 3 −-N contents. • Substrate availability and microbe drive SOC mineralization in permafrost peatlands. Permafrost peatlands are important pools of soil carbon. Soil organic carbon (SOC) mineralization and its temperature sensitivity in permafrost peatlands are crucial for predictions of soil carbon-climate feedback. However, little is known about the changes in SOC mineralization and its mechanism in response to environmental change in the permafrost peatlands of Northeastern China. We collected seven permafrost peatland soils from Greater and Lesser Khingan Mountains in Northeastern China to investigate how the responses of microbes and labile substrates control the mineralization of SOC in the laboratory incubation study. The results show that temperature and sampling sites affected the mineralization of SOC. Elevated temperatures significantly increased the rate of carbon mineralization across the peatland soils. The mean sensitivity of SOC mineralization to temperature (Q 10 value) was 2.96. The increase in substrate availability and microbial abundance in parallel with the increase in temperature is responsible for the high rates of decomposition of the organic carbon pools. We found that the mineralization of soil carbon positively correlated with the concentrations of soil dissolved organic carbon (DOC), NH 4 +-N, NO 3 −-N, as well as the abundances of bacteria, fungi, methanotrophs and nir K denitrifiers. Moreover, the content of DOC positively correlated with the abundances of soil bacteria, methanotrophs and nir K denitrifiers, indicating that the influences of soil microbial abundances on carbon mineralization were strongly mediated by the availability of carbon substrates. Our findings provide novel insights into the effects of increasing temperatures on the relationship between microbial communities and labile substrates and their roles in carbon decomposition in permafrost peatlands. [ABSTRACT FROM AUTHOR]

• Warming increases soil C cycling microbial abundance, which will result in C loss. • Soil nif H and nir K gene abundances exhibit insensitivity to 6 years of warming. • Soil β-glucosidase, inverse, and urease respond differently to 6 years of warming. • Warming accelerates DOC decomposition and leaching from shrub non-rhizosphere soil. • No warming effect is observed on soil TC, MBC, and NO 3 −–N content. Soil microbes and enzymes in permafrost peatland are sensitive to temperature changes, which might result in more potential loss of carbon and increase in available nitrogen from permafrost peatlands in a warming world. We previously demonstrated that 3-year warming could affect soil microbial abundance and enzymatic activity. However, soil microbial abundance and enzymatic activity in permafrost peatlands under long-term climate warming is not well understood. Therefore, a 6-year field manipulation experiment was used to assess the impact of long-term warming on soil microbial abundance and enzymatic activity in a permafrost peatland in northeastern China. Results showed that 6-year warming increased the abundance of bacteria in 0 to 15 cm soil under tussock and from shrub rhizosphere, fungi from shrub non-rhizosphere, and archaea under tussock and from the rhizosphere of shrub. These increased microbial abundances could stimulate soil carbon cycling and accelerate soil carbon loss in permafrost peatland under warming. Six-year warming increased methanogen abundance in 0 to 15 cm soil and methanotroph abundance in 15 to 30 cm soil under tussock, indicating that warming could enhance CH 4 cycling. Soil nir S-denitrifier abundance from the 0 to 15 cm shrub rhizosphere increased under warming, thereby suggesting that warming stimulated denitrification and N 2 O emission. β-Glucosidase activity in 0 to 15 cm soil under tussock and from shrub rhizosphere increased, but invertase activity in 15 to 30 cm soil under tussock and from shrub rhizosphere showed opposite tendency under warming. DOC content tended to increase in the 0 to 15 cm rhizosphere soil, but decreased in shrub non-rhizosphere soil. Warming increased NH 4 +–N content in both rhizosphere and non-rhizosphere soil. Positive correlations between abundances of bacteria, archaea, contents of DOC, and NH 4 +–N in 0 to 15 cm soil suggest that increases in bacterial and archaeal abundance could indicate higher carbon and nitrogen availability in topsoil of permafrost peatlands under warming. The results offer new insights into the response of plant–soil-microbe interactions in permafrost peatlands to climate change. [ABSTRACT FROM AUTHOR]

Peatlands in permafrost region are large carbon pools sensitive to global warming. However, the effects of increased temperature on carbon emissions and associated microbial abundances of peatlands under anaerobic condition remain largely unknown, especially when considering depths. For supplementing the deficiency about this, we collected soil from 0 to 150 cm depth of a permafrost peatland in the Great Hing'an Mountain and incubated at 5 and 15 °C for 55 days under anaerobic condition. Soil CO 2 and CH 4 emissions were detected during incubation, and inorganic nitrogen, dissolved organic carbon, and carbon-cycling microbial abundances were analyzed at the end of incubation. Results showed that emission rates and cumulative emissions amount of CO 2 and CH 4 at 15 °C across all soil depths were higher than those observed at 5 °C. Specifically, 0–20 cm and 20–40 cm layers had the highest CO 2 emission rates and cumulative emission amounts, whereas the 40–60 cm and 60–80 cm layers had the highest CH 4 emission rates and cumulative emission amounts. Mean temperature sensitivity (Q 10) values of CO 2 and CH 4 were 2.39 and 55.49 respectively. Q 10 values of bacteria, fungi, archaea, methanogen, and methanotroph abundances were 1.17, 3.85, 1.75, 1.68, and 1.66 respectively, which were calculated by the abundance ratio of microbial functional gene at 15 °C and 5 °C. Similar to the trend of CO 2 emissions, high bacteria, fungi, archaea, methanogen, and methanotroph functional gene abundances were also observed in 0–20 cm and 20–40 cm layers, and such abundances increased along with temperature increasing. In sum, elevated temperature enhances the carbon emission of peatland in permafrost region, and the warming simulated CO 2 emission is linked to the abundances of carbon-cycling microorganisms. • Soil CO 2 and CH 4 emissions at 15 °C are higher than at 5 °C across all soil depths. • Active layer soil has the highest CO 2 emission amounts in permafrost peatland. • CH 4 emissions are highest in the transition layer and its adjacent active layer. • Warming stimulated CO 2 emission is linked to C-cycling related microbial abundance. [ABSTRACT FROM AUTHOR]

• Permafrost types affect soil microbial abundance distribution in peatlands. • NH 4 +-N, pH, and total C are crucial in changing soil microbial abundance. • Archaea are relatively stable in different types of permafrost peatlands. • pmo A, mcr A and nir S gene abundances can be used as TC and TN indicators in peatlands. Soil microbial abundance, which is related to soil characteristics and process rates, is an early indicator of changes in soil health and quality. However, microbial functional groups in permafrost peatland soils have rarely been studied. These soils are important C and N stores and possibly vulnerable to climate warming. We randomly gathered surface soils (0–15 cm and 15–30 cm soil layers) from 10 peatlands in sporadic island, discontinuous island, and continuous permafrost regions in Northeast China. The aim was to clarify the soil microbial abundance distribution in different types of permafrost peatlands. Results revealed different effects of permafrost types on different soil C- and N-cycling microbial abundances in peatlands. The bacteria, amo A, and nir K gene abundances in the two soil layers were the highest in discontinuous island permafrost peatlands. Soil mcr A and pmo A gene abundances in 0–15 cm soil were high in continuous and discontinuous island permafrost peatlands, respectively. The amo A gene abundance in both soil layers and nir S gene abundance in 15–30 cm soil were high in discontinuous island permafrost peatlands. The average nir K gene abundance in both soil layers was in the order: discontinuous island permafrost peatlands > continuous permafrost peatlands > sporadic island permafrost peatlands. No significant differences in archaeal abundance were observed in both soil layers among the different types of permafrost peatlands. Moreover, 42.5%, 15.9%, and 15.3% of the variation in soil microbial abundances could be explained by soil ammonia-N, pH, and total C, respectively. Our results imply that soil microbial abundance can be utilized as effective soil N availability, C pool, and pH indicators in permafrost peatlands. [ABSTRACT FROM AUTHOR]

Global warming may have a great impact on soil organic carbon (SOC) turnover in permafrost peatlands. The response of microbial residues, as precursors of SOC, to climate warming remains unknown. A 6-year in situ warming experiment was conducted in the permafrost peatlands of Great Hing'an Mountains. Three commonly used amino sugars (glucosamine, GluN; galactosamine, GalN; muramic acid, MurA), for the quantification of microbial residues, were determined in two depths (0–15 cm, shallow soil; 15–30 cm, deep soil) of the bulk and rhizosphere soil of the shrub and Eriophorum vaginatum L. The amount of GluN, GalN, and MurA in deep shrub rhizosphere soil in the warming treatment decreased by 12.65%, 26.11%, and 14.78%, respectively, as compared to that in the control treatment. Yet, warming did not alter the amount of amino sugars in shallow and deep bulk soil. Warming decreased the concentrations of GluN, MurA, and total amino sugars in the deep rhizosphere soil of Eriophorum vaginatum L. by 22.04%, 26.14%, and 18.71%, respectively. Amino sugars in the deep rhizosphere soil of Eriophorum vaginatum L. had a higher temperature sensitivity than those in the deep bulk soil, while total amino sugars in the shallow rhizosphere soil of Eriophorum vaginatum L. had a lower temperature sensitivity than those in the deep rhizosphere soil. • Warming decreased deep rhizosphere soil amino sugars in permafrost peatlands. • Warming did not affect amino sugars in bulk soil. • Amino sugars contributed slightly to SOC in permafrost peatlands. [ABSTRACT FROM AUTHOR]

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 Q 10 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. [ABSTRACT FROM AUTHOR]

Abstract: Soil thawing may affect the turnover of soil organic carbon (C) and the release of C to the atmosphere. Little is known about C release during thawing in the Great Hing'an Mountains, China. Through the incubations, we studied the emissions of CO2 and CH4 during thawing from the Sphagnum moss layer to the permafrost layer under aerobic and anaerobic conditions. Carbon was released quickly during thawing under different conditions. The Sphagnum moss layer produced more CO2 than the other layers. However, there was little CH4 release during thawing in the Sphagnum moss layer and burst of CH4 emissions in the peat and permafrost soils. These bursts include stored CH4 in the frozen samples and productions from microbial activity. The temperature sensitivity during thawing decreased across the freezing point in the Sphagnum moss layer, did not change greatly in the root layer, and increased greatly in the peat and permafrost layers. Changes in soil substrates and enzyme activities may affect C release during thawing. [Copyright &y& Elsevier]

Abstract: Wetlands in mid-high latitude regions play a vital role in climate change, due to their high organic carbon density. Nonetheless, the stabilization of soil organic carbon (SOC) and its fractions in these regions is largely unknown. The objectives of this study were to examine the changes in SOC and its fractions along a latitudinal gradient and to analyze the influencing factors in the southern margin of the permafrost region on the Eurasian continent. Topsoil (0–20cm) was collected from five wetlands along a latitudinal gradient in Northeast China. We analyzed SOC and some labile fractions. Our results demonstrated that wetland SOC and its labile fractions concentration declined with decreasing latitude. The Permafrost regions had greater organic carbon content than the regions with seasonally frozen ground. The light fraction organic carbon and particulate organic carbon accounted for 5–83% and 21–32%, respectively, of the SOC and were particularly enriched in the permafrost region. Microbial biomass carbon and dissolved organic carbon showed a similar decreasing trend to that of SOC. At the same latitude, vegetation affected SOC stock and the dynamics of its labile fractions. Therefore, wetlands in mid-high latitudes contain a large carbon pool, and carbon stock varies with latitude. Although the labile fractions were higher in the permafrost region, their activities were lower, due to low temperature and poor nutrient status. Under global warming, the labile carbon pool may be mobilized and contribute to the greenhouse effect. Moreover, vegetation differences should be considered in obtaining an accurate carbon calculation. [Copyright &y& Elsevier]