Search

Background and aims: Nitrogen (N) is often the nutrient limiting the decomposability of shoots from macrophytes in wetlands. We aimed to determine the effects of increasing soil N availability on the decomposition of shoots during the standing-dead phase. Methods: We measured the quality of senesced leaves from graminoids and their subsequent aerial decay under different N addition treatments (Control, 0 kg N ha yr.; N60, 60 kg N ha yr.; N120, 120 kg N ha yr.; N240, 240 kg N ha yr.) in a temperate marsh. Results: Nitrogen addition increased N concentrations in senesced leaves and often increased phosphorus (P) concentrations. The exponential decay constants ( k) of leaves from the N120 and N240 treatments were higher than the control treatment during aerial decay. Nitrogen amounts (in percentage terms) remaining in decaying leaves always significantly decreased after N addition, but the effects on P amounts varied with N addition rates. The nutrient amounts remaining in leaves during the standing-dead phase had negative relationships with the initial nutrient concentrations. Conclusions: Soil N availability exerts remarkable effects on the decay process of standing litters by altering the initial quality, and thus the biogeochemical cycling in temperate wetlands. [ABSTRACT FROM AUTHOR]

The graphene nanoplates (GNPs) reinforced TiNiCu (53Ti-23.5Ni-23.5Cu, at.%) filler materials (abbreviated as G-TNC) were innovatively developed and adopted in the form of multi-layers (G-TNC/Nb/Ti) to braze laser-modified C f /SiC and GH99. The corresponding typical interfacial microstructure of the joint was studied and its evolution with GNPs content and brazing temperature was elucidated in detail. The joining mechanism demonstrates that the Ti 2 (Ni,Cu) in filler materials firstly melted to be L1 and then dissolved Nb foil to form L2 which was the decisive factor for forming joint. The Ti 2 (Ni,Cu) content was regulated by GNPs, which decreased after increasing GNPs content. With the proper GNPs content of 0.3 wt%, the sound C f /SiC/GH99 joint with maximum average shear strength was obtained and the brazed seam was occupied by ductile Ti(Ni,Cu) + (Nb,Ti)ss with dispersedly distributed (Ti,Nb)C particles. The corresponding strength of joint was 77.9 MPa at room temperature and 67.3 MPa at high temperature (800 °C), which separately increased by 22.8% and 46.3% than that of joints without introducing GNPs. When the GNPs content exceeded 0.3 wt%, the decreased content of L1 caused L2 deficiency, hence, the joint was weakened and its performance was deteriorated. Neither increasing GNPs content nor brazing temperature could optimize the strength of joints. • The GNPs - TiNiCu filler material and the reaction mechanism between it and Nb were clearly studied by SEM, TEM and DSC. • The effective method of combining surface modification and composite brazing was proposed to strengthen joints. • The effect of GNPs and brazing temperature on microstructure evolution and mechanical properties of joints were clarified. • The room temperature and high temperature strength of joint were improved by 22.8% and 46.3% by using 0.3 wt.% G - TNC [ABSTRACT FROM AUTHOR]

Litter decay is a fundamental process in ecosystem carbon flux and nutrient cycling. In wetlands, shoot litters on the sediment surface and in the air are important components of the detritus pool. We used the litterbag method to compare mass losses and nutrient dynamics of culms, sheaths, and leaves from Deyeuxia angustifolia on the sediment surface and in the air from October 2011 to October 2012 in a freshwater marsh in Northeast China. The mass losses for the three litters in the air were only approximately 3% and less than that on the sediment surface after 180 days of decay, but increased to 16–44% after one year of decay and thus exceeded or approached that of surficial corresponding litters. For leaves and sheaths, the increased nutrient (nitrogen and phosphorus) concentrations of aerial litters resulted in an approximately 10% increase in the nutrient amounts after 180 days of decay, which was greater than that of surficial corresponding litters; however, surficial litters exhibited a greater increase or a lesser decrease of nutrient amounts than did aerial corresponding litters after one year of decay. For culms, the litter nutrient amounts in the air were always more or not less than those on the sediment surface during one year of decay, although effects of the litter position on nutrient concentrations were negligible (for nitrogen) or varied over time (for phosphorus). Overall, the litter position significantly affected the decay processes in this marsh. Therefore, it is essential to consider litter mass and decay processes at different positions to comprehensively understand carbon cycle and nutrient turnover in temperate freshwater marshes. [ABSTRACT FROM AUTHOR]

• The impacts of wetland conversion on soil microbes vary over season and along soil profile. • The homogenization impact is the strongest in summer and weakest in winter. • Wetland reclamation suppresses microbial diversity in winter, spring, and summer. • The input of fresh carbon in autumn enhances microbial diversity. Soil microbes drive biogeochemical cycles of carbon (C) and nutrients, and land conversion alters soil microbes and thus, affects C and nutrient cycling at the ecosystem level. To evaluate the impacts of wetland reclamation on microbes along soil profiles and over seasons, soil cores (0–100 cm) were collected from a natural wetland and an adjacent cropland that has been continuously cultivated for 23 years in the Sanjiang Plain, northeastern China. Wetland conversion to cropland generally homogenized the microbial abundance along the soil profiles in four seasons (May of spring, July of summer, October of autumn, and December of winter), while the vertical homogenization was the strongest in summer and weakest in winter. After 23 years of cultivation, the abundances of fungi and bacteria in surface soils were significantly reduced by approximately 90% and 80%, respectively, whereas the bacterial abundances increased and fungal abundances decreased in middle and deep soils, suggesting that cultivation impacts on microbial community structure varied along soil layers. Compared to the wetland, total phospholipid fatty acids in the middle and deep soils of the cropland were enhanced by approximately 60–367% in autumn and winter and 30–137 % in spring and summer. Wetland reclamation suppressed the microbial diversity in the surface soils in winter, spring, and summer but stimulated that in autumn, indicating robust enhancements on microbial diversity by the inputs of fresh litter C. The quantifications of microbial abundance and community structure showed the non-uniform impacts of wetland reclamation on microbes along the soil profile and over seasons, which provides valuable information for benchmarking models in simulating microbial roles on C cycling in deep soils at the seasonal scale. [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]

Abstract: Wetland ecosystems store a large amount of organic carbon (C) in soils, due to the slow decomposition rates of plant litter and soil organic matter. Increased nitrogen (N) availability induced by human activities and global warming may accelerate litter decomposition and affect soil organic C dynamics in wetlands. In the present study, we investigated the effect of N addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes in the Sanjiang Plain of Northeast China under field and laboratory conditions. First, we assessed the changes in initial litter chemical composition and subsequent decomposition following three years of N addition at the rate of 24gNm−2 year−1 under field conditions. Our results showed that N addition increased litter N concentration and decreased C/N ratio, and thus stimulated litter decomposition. Secondly, we examined the effect of increased N availability (0, 25, 50 and 100mgNg−1 litter) on litter decomposition under laboratory conditions. Increased exterior N availability also enhanced microbial respiration and increased litter mass loss under both waterlogging and non-waterlogging conditions. In addition, waterlogging conditions inhibited microbial respiration and suppressed litter mass loss. These findings demonstrated that N addition increased litter decomposition rates through improved litter quality and enhanced microbial activity in freshwater marshes of Northeast China. This implies that increased N availability accelerates litter decomposition rates, and thus may cause substantial losses of soil C and diminish and even reverse the C sink function of wetlands in the Sanjiang Plain of Northeast China. [Copyright &y& Elsevier]

• VPD stress is stronger in grassland under dry condition than in forest and shurbland. • Negative VPD impacts are positively regulated by SWC in grassland. • GPP is mostly controlled by VPD in forest and shurbland and by SWC in grassland. Atmospheric water demand is practically characterized as vapor pressure deficit (VPD) and has been identified as a critical driver of ecosystem function, by affecting plant mortality, wildfires, and carbon loss. In this study, we used daily eddy covariance data across Chinese forest, grassland and shrubland ecosystems, in combination with remote sensing data, to investigate the impacts of VPD on gross primary productivity (GPP). We found divergent VPD impacts on GPP among grassland, shrubland and forest ecosystems. The VPD yielded substantial inhibitory impacts on GPP in grassland ecosystems and this suppressing impact was regulated by soil water content (SWC), showing that GPP declined with VPD under dry conditions but increased with VPD under wet conditions. This GPP variance was attributed to VPD, SWC and their interactions. More than 50% of the variability in GPP was explained by SWC in grassland ecosystems and by VPD in forest and shrubland ecosystems. Partial correlation analysis, random forest, and multiple linear regression revealed similar results when temperature, radiation and SWC were considered. Compared with shrubland and forest ecosystems, grassland has drier environmental conditions and poorer soil water-holding capacity that led to lower SWC and stronger negative impacts on VPD. Thus, GPP was susceptible to the negative impacts of higher VPD, especially under dryness stress. Our results highlight the need to comprehensively consider divergent VPD impacts for different ecosystems to more accurately assess climate impacts on ecosystem function. [ABSTRACT FROM AUTHOR]

• Wetland reclamation homogenized microbial biomass along soil profile. • Cultivation narrowed the C:N:P:S stoichiometry in soils and microbial biomass. • Cultivation promoted bacterial abundance in 30–80 cm soil profile. Wetlands store approximately one-third of soil carbon (C) in terrestrial ecosystems, and the loss of C in wetlands has been accelerated by reclamation. However, how wetland reclamation affects microbial properties along soil profiles remains unclear. In this study, we sampled 100 cm soil cores from a wetland and an adjacent cropland that has been cultivated for 23 years to evaluate the impacts of land conversion on soil microbial community structure and soil element concentrations in the Sanjiang Plain, Northeastern China. The C and nitrogen (N) concentrations in microbial biomass declined exponentially with depth in both the wetland and cropland with different magnitudes. Continuous cultivation for 23 years tended to homogenized C, N, phosphorus (P), and sulfur (S) contents in soils and microbial biomass along the soil profile. Compared with the wetland, C and N in cropland soils were lower, and microbial biomass C, N, P and S were lower in surface soils (0–30 cm), while higher in both middle soils (40–70 cm) and deep soils (70–100 cm). Cultivation narrowed the C:N:P:S stoichiometry in soils and microbial biomass, with large changes in surface soils and minor changes in deep soils. The Bray-Curtis dissimilarity test confirmed the large changes in surface soils while minor changes in deep soils. After 23-years of cultivation the abundances of fungi and bacteria were significantly reduced by approximately 90% and 78% in surface soils, but the bacterial abundance was enhanced by approximately 2–3 times in middle soils, leading to a decreasing fungi:bacteria ratio along soil profile in cropland. Soil TC and pH were the predominant factors controlling the microbial composition in wetland. The homogenizing impact of wetland reclamation on microbial properties along soil profiles suggests the different responses of microbial and soil elements to human activities, indicating a critical need of differentiating microbes from soils when examining soil elements under a changing environment. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Rising vegetation activity dominates the climbing water use efficiency in the Asian permafrost region from 1900 to 2100. • Large spatial heterogeneities in water and carbon fluxes were observed in the study domain. • The CMIP6 models projected substantial increases in GPP and NPP while slight increase in evapotranspiration during 2010-2100. [ABSTRACT FROM AUTHOR]