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 Q10 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.
•Peat soil labile C is the main driving force of microbial mineralization activity.•Soil C and N mineralization in peatland increase with elevated temperature.•Increasing temperature significantly decreases soil MBC and DOC in peatland.•Root additions increase soil C mineralization and stimulate soil invertase activity.
•Rising temperature accelerated the mineralization of SOC in permafrost peatlands.•Q10 of SOC mineralization ranged from 2.24 to 4.22 among 7 permafrost peatlands.•SOC mineralization positively ...correlated with soil DOC, NH4+-N, NO3−-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 (Q10 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), NH4+-N, NO3−-N, as well as the abundances of bacteria, fungi, methanotrophs and nirK denitrifiers. Moreover, the content of DOC positively correlated with the abundances of soil bacteria, methanotrophs and nirK 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.
•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 permafrostpeatlands, we selected two typical plants, Eriophorumvaginatum and Sphagnumpalustre, 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 CO2 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 CO2 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.
•Warming increases soil C cycling microbial abundance, which will result in C loss.•Soil nifH and nirK 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 NO3−–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 CH4 cycling. Soil nirS-denitrifier abundance from the 0 to 15 cm shrub rhizosphere increased under warming, thereby suggesting that warming stimulated denitrification and N2O 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 NH4+–N content in both rhizosphere and non-rhizosphere soil. Positive correlations between abundances of bacteria, archaea, contents of DOC, and NH4+–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.
This paper developed an innovative pressure-free contact reaction brazing technique that facilitated joining ceramics at low temperatures. Using this method, a semi-solid TiNiCuNb filler was employed ...to join C/C–SiC composite and Ti60 alloy. By facilitating elements’ diffusion through the partial liquid of semi-solid TiNiCuNb alloy, Ti could be introduced into this alloy without pressure, and the complete melting was achieved above 950 °C. Based on this, Ti60 alloy was joined to C/C–SiC composite below its β-transus temperature. Significant reaction differences between C/C and SiC with filler were found, mainly due to the different solubility and diffusion characteristics of C and Si in liquid filler. SiC exhibited higher sensitivity to temperature changes and was more prone to overreaction to induce defects. At 1010 °C, the maximum shear strength of 22.5 MPa was obtained due to the moderate reaction of both C/C and SiC with filler. This work contributed to manufacturing lightweight brake systems.
Abstract
Recent studies have reported worldwide vegetation suppression in response to increasing atmospheric vapor pressure deficit (VPD). Here, we integrate multisource datasets to show that ...increasing VPD caused by warming alone does not suppress vegetation growth in northern peatlands. A site-level manipulation experiment and a multiple-site synthesis find a neutral impact of rising VPD on vegetation growth; regional analysis manifests a strong declining gradient of VPD suppression impacts from sparsely distributed peatland to densely distributed peatland. The major mechanism adopted by plants in response to rising VPD is the “open” water-use strategy, where stomatal regulation is relaxed to maximize carbon uptake. These unique surface characteristics evolve in the wet soil‒air environment in the northern peatlands. The neutral VPD impacts observed in northern peatlands contrast with the vegetation suppression reported in global nonpeatland areas under rising VPD caused by concurrent warming and decreasing relative humidity, suggesting model improvement for representing VPD impacts in northern peatlands remains necessary.
Changes in soil CO
2
and N
2
O emissions due to climate change and nitrogen input will result in increased levels of atmospheric CO
2
and N
2
O, thereby feeding back into Earth’s climate. ...Understanding the responses of soil carbon and nitrogen emissions mediated by microbe from permafrost peatland to temperature rising is important for modeling the regional carbon and nitrogen balance. This study conducted a laboratory incubation experiment at 15 and 20°C to observe the impact of increasing temperature on soil CO
2
and N
2
O emissions and soil microbial abundances in permafrost peatland. An NH
4
NO
3
solution was added to soil at a concentration of 50 mg N kg
−1
to investigate the effect of nitrogen addition. The results indicated that elevated temperature, available nitrogen, and their combined effects significantly increased CO
2
and N
2
O emissions in permafrost peatland. However, the temperature sensitivities of soil CO
2
and N
2
O emissions were not affected by nitrogen addition. Warming significantly increased the abundances of methanogens, methanotrophs, and
nir
K-type denitrifiers, and the contents of soil dissolved organic carbon (DOC) and ammonia nitrogen, whereas
nir
S-type denitrifiers, β-1,4-glucosidase (βG), cellobiohydrolase (CBH), and acid phosphatase (AP) activities significantly decreased. Nitrogen addition significantly increased soil
nir
S-type denitrifiers abundances, β-1,4-N- acetylglucosaminidase (NAG) activities, and ammonia nitrogen and nitrate nitrogen contents, but significantly reduced bacterial, methanogen abundances, CBH, and AP activities. A rising temperature and nitrogen addition had synergistic effects on soil fungal and methanotroph abundances, NAG activities, and DOC and DON contents. Soil CO
2
emissions showed a significantly positive correlation with soil fungal abundances, NAG activities, and ammonia nitrogen and nitrate nitrogen contents. Soil N
2
O emissions showed positive correlations with soil fungal, methanotroph, and
nir
K-type denitrifiers abundances, and DOC, ammonia nitrogen, and nitrate contents. These results demonstrate the importance of soil microbes, labile carbon, and nitrogen for regulating soil carbon and nitrogen emissions. The results of this study can assist simulating the effects of global climate change on carbon and nitrogen cycling in permafrost peatlands.
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Underwater wet flux-cored arc welding of Q460 steel using specially developed Ni-based filler and commercially obtained ER308 were investigated. Wet welded joints using Ni-based ...filler were of high performance with high ultimate tensile strength (518MPa) and impact toughness of the weld metal (128.9J/cm2). ER308 failed to acquire sound welded joints due to extensive slag remained in the bottom of groove. The highest microhardness (450 HV) was recorded on the coarse-grained heat-affected zone of the base metal for both joints. TypeⅡboundaries existed in the interfaces between austenitic weld metal and ferritic base metal. Compared to austenitic stainless steel weld metal, nickel-based weld metal possessed the ability to be significantly diluted by Q460 base metal.
Vacuum brazing of Zr and 316 stainless steels (316L) was conducted using a Zr
74
Cu
13
Fe
13
(at%) amorphous filler. A comprehensive investigation was carried out to examine the interfacial ...microstructure and mechanical properties of Zr/316L joints under varying brazing temperatures and extended holding times. The reaction products in Zr/316L joints brazed at 980 °C for 10 min consisted of Zr
2
Fe + Zrss/Zr(Fe,Cr)
2
+ (Zr,Cu)/α-(Fe,Cr). As the temperature increased and the duration of holding was extended, both Zr(Fe,Cr)
2
and α-(Fe,Cr) layers adjacent to 316L thickened. Particularly, the growth kinetics analysis of the diffusion zone revealed that the growth coefficient of Zr(Cr,Fe)
2
and α-(Fe,Cr) were 0.0291 μm
2
/s and 0.0058 μm
2
/s, respectively, indicating that Zr(Cr,Fe)
2
exhibited a higher thickening rate than α-(Fe,Cr). The shear strength of Zr/316L joints initially increased and then deteriorated with higher brazing temperatures or longer holding times. The Zr/Zr–Cu–Fe/316L joints achieved a maximum strength of 93.5 MPa at a brazing parameter of 980 °C/15 min. Additionally, the joints initially failed at the interface of Zr(Fe,Cr)
2
/316L, with cracks propagating along the brittle Zr
2
Fe phase within the brazing seam.
Graphical 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.
► Labile SOC fractions in wetland along a latitudinal gradient were investigated. ► Wetland SOC and its labile fractions declined within decreased latitude. ► Labile fractions were enriched in permafrost region but their activities were lower. ► In the same latitudes, vegetation affected SOC stock and labile fractions dynamics. ► Low temperature and poor nutrient led to large SOC stocks in mid-high latitudes.
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