Cycling Processes Research Articles

Drivers of denitrification and nitrification in a dryland agroecosystem: The role of abiotic and biotic factors

Agricultural practices such as tillage and fertilization impact soil nitrogen (N) cycling processes, but how they alter the coupling between the activity, abundance and diversity of N-cycling microbes remains to be understood. Here, we used a fifteen-year trial in a dryland agroecosystem on the Loess Plateau of China (two tillage regimes crossed with six fertilization treatments) to understand how (de)nitrification potentials are determined by soil abiotic conditions and the abundances and compositions of the (de)nitrifier communities. We measured the abundances of bacterial (AOB) and archaeal (AOA) ammonia oxidizers and nirK- and nirS-nitrite reducers, their community compositions, potential nitrification (PNA) and denitrification (PDA), and soil abiotic conditions. PNA and PDA across the 12 treatments were positively correlated to AOB abundance and nirS abundance, respectively. Co-occurrence network analysis revealed the presence of dominant ecological modules of (de)nitrifiers sensitive to agricultural treatments, and more complex network under no-tilled than tilled conditions as well as under multiple fertilizers than unfertilized conditions. Path analysis and random forest analysis both showed that PNA was explained by AOB abundances and the relative abundance of one module of (de)nitrifiers driven by soil ammonium concentration, while PDA was most related to soil organic carbon concentration, pH and to a lesser extent nirS abundance. These findings demonstrate that, in agricultural soils, the potential of denitrification –a facultative activity for denitrifiers– is mainly predicted by abiotic conditions, while the potential of nitrification –an obligate activity for nitrifiers– is determined by biotic variables, here AOB abundances and a particular cluster of microbial populations.

Facile synthesis of Co/Fe bimetallic doped Ni3S2 nanosheets and supercapacitor performance

Ni3S2 is an outstanding electrode material due to its high theoretical specific capacity, however, in practical research, the higher theoretical capacity is difficult to show, and the change of the structure in the cycling process affects the cycling stability, which limits its practical application. To address these issues, this study presents a strategy to synthesize Fe and Co bimetallic doped Ni3S2 nanosheets on nickel foam (NF) surface. This strategy introduces bimetallic atoms quickly and easily while synthesizing nanosheet structures, and the resulting synergistic interactions between the bimetals and the mutual support effect of the nanosheets can effectively enhance electron transfer and improve cycling stability. The electrochemical results show that the Fe and Co-doped sample (Ni3S2-Co/Fe-5) exhibits a specific capacitance of 3351 F·g−1 at 1 A·g−1 in the three-electrode system, which is nearly five times higher than the specific capacity of the undoped Fe and Co-doped sample (Ni3S2), and the capacity retention rate after cycling 5000 cycles at a current density of 10 A·g−1 is 100 %, the prepared sample (Ni3S2-Co/Fe-5) was assembled with activated carbon (AC) to form a hybrid supercapacitor, which could provide a maximum power density of 9818 W·kg−1, a maximum energy density of 66.25 Wh·kg−1, and a capacity retention of 94.5 % after 10,000 cycles, with a capacity loss of only 5.6 %.

Er-modified AlSi7Mg alloy with high-density cellular structure and nano precipitates produced by selective laser melting

The multiple thermal cycling processes during the selective laser melting (SLM) produce unique microstructure in AlSi7Mg alloy, and the addition of Er significantly affects the microstructure evolution under the thermal cycling. Due to the rapid solidification during the gas-atomization and SLM, the elements distribute uniformly in gas-atomized powder, and high-density cellular structure and nano precipitations form in as-built AlSi7Mg alloy. The addition of Er promotes the formation of coherent Al3Er nano particles through in-situ reaction, which act as the cores of heterogeneous nucleation and pin the subgrain boundaries, and result in higher fraction of fine equiaxed grains and substructure in Er-modified AlSi7Mg.

Dual Redox Reactions of Silver Hexacyanoferrate Prussian Blue Analogue Enable Superior Electrochemical Performance for Zinc‐ion Storage**

AbstractPrussian blue analogues (PBAs) have been employed as host materials of aqueous zinc‐ion batteries (ZIBs), however, they suffer from low capacity and poor cycling stability due to limited electron transfer and the presence of interstitial water in PBAs. Herein, a vacancy and water‐free silver hexacyanoferrate K0.95Ag3.05Fe(CN)6 (AgHCF‐3) was synthesized by adjusting the ratio of K and Ag in the framework. It offers nearly four electrons involving two sequential redox reactions, namely, Fe3+/Fe2+ and Ag+/Ag0, to deliver a large capacity of 179.6 mAh g−1 at 20 mA g−1 with Coulomb efficiency of ~100 %. The Zn//AgHCF‐3 cell delivers an estimated energy density of 200 Wh kg−1, surpassing reported PBAs‐based ZIBs. The formation of Ag0 in the cycling process merits favorable rate performance of AgHCF‐3 (156.4 mAh g−1 at 200 mA g−1 with 80.3 % capacity retention after 100 cycles). This investigation paves new pathways for high‐capacity PBA cathodes.

Waxberry-like TiO2 with Synergistic Surface Modification of Pyrolytic Carbon Coating and Carbon Nanotubes as an Anode for Li-Ion Battery.

Titanium dioxide (TiO2) as an anode material for lithium-ion batteries (LIBs) has the advantages of tiny volume expansion, high operating voltage, and outstanding safety performance. However, due to the low conductivity of TiO2 and the slow diffusion rate of lithium ions (Li+), it is limited in the application of LIBs. Therefore, waxberry-like TiO2 comodified by pyrolytic carbon coating and carbon nanotubes was prepared in this work. The waxberry-like TiO2 with nanorods on its surface shortens the diffusion distance of Li+. Carbon nanotubes and waxberry-like TiO2 are tightly combined through electrostatic assembly and form a cross-linked conductive network to provide more electron transmission paths. A thin layer of pyrolytic carbon wraps carbon nanotubes and waxberry-like TiO2, which enhance the conductivity of the composites and ensure the structural integrity of the materials throughout the cycling process. The experimental data revealed that the discharge-specific capacity of TiO2@CNT@C is 170.5 mAh g-1 after 3000 cycles at a large current density of 5 A g-1, and the discharge-specific capacity is still 143 mAh g-1 at the superhigh rate of 10 A g-1, which provides excellent rate performance and cyclic stability. The efficient dual-carbon modification strategy could potentially be extended to other materials.

Accelerated Ion-Electron Transport in Bi-Heterostructures Constructed Based on Ohmic Contacts for Efficient Bi-Directional Catalysis of Lithium-Sulfur Batteries.

Although lithium-sulfur batteries have satisfactory theoretical specific capacity and energy density, they are difficult to further commercialize due to the shuttle effect of soluble polysulfides and slow sulfur oxidation kinetics. Based on this, in this work, the catalyst MXene-VS4-SnS2 (MVS), a dual heterostructured catalyst with ohmic contacts, is prepared by a one-step hydrothermal method and electrostatic self-adsorption for lithium-sulfur battery cathode materials. Experimental and theoretical results show that the ohmic contact induces spontaneous charge rearrangement, resulting in the formation of a fast charge transfer pathway at the MVS heterojunction interface, which helps to reduce the energy barrier for polysulfide reduction and Li2S oxidation during the discharge/charge process. In addition, the inherent sulfophilicity of VS4 and SnS2 promotes the conversion of S species, while the pleated MXene nanosheets not only provide a highly conductive network for the active sulfur but also retain a rich internal space to maintain the integrity of the cathode structure during the continuous cycling process. As a result, the MVS cathode exhibits excellent electrochemical performance even under high sulfur loading. The integration of excellent performance with a facile synthesis process provides a promising approach for designing highly efficient electrocatalysts suitable for the energy field.

Spatio-temporal distribution and biotechnological potential of culturable yeasts in the intertidal sediments and seawater of Aoshan Bay, China.

Marine yeasts play a crucial role in marine microbial ecology, facilitating the biogeochemical cycling of carbon and nitrogen in marine ecosystems, while also serving as important reservoirs of bioactive compounds with extensive applications in pharmaceuticals, agriculture, and various industries. Intertidal flats, characterized by their complex ecological dynamics, are postulated to harbor a wealth of yeast resources. This study employed a culture-dependent approach to assess the diversity, spatio-temporal distribution, and biotechnological potential of yeast communities residing within the intertidal sediments and seawater of Aoshan Bay. A total of 392 yeast strains were identified from 20 distinct genera, encompassing 43 recognized species and four candidate novel species. Notably, 17 of these species were identified as novel occurrences in marine environments, underscoring the rich yeast biodiversity of the Aoshan Bay ecosystem, with Candida emerging as the dominant genus in both sedimentary and aqueous habitats. Yeast community composition exhibited significant spatial and temporal variation, with peak diversity and abundance observed in autumn, the subtidal zone, and the surface soil layer. No clear pattern, however, emerged linking these shifts to specific changes in community composition, highlighting the complex interactions between microbial communities, environmental variables, and anthropogenic disturbance. Although several yeast species isolated here have been previously recognized for their biotechnological potential, their diverse and abundant extracellular enzyme profiles were characterized, further highlighting their crucial role in organic matter decomposition and nutrient cycling within the tidal ecosystem, as well as their potential applicability in the food, fine chemical, textile, and pharmaceutical industries.IMPORTANCEThis study presents groundbreaking insights into the yeast diversity of Aoshan Bay, offering invaluable information on their spatial and temporal distribution patterns, as well as their biotechnological potential in the tidal environment. The findings reveal that the eutrophic intertidal flat is a rich repository of yeasts with abundant extracellular enzymatic activity and an important role in nutrient cycling and decomposition processes. Also, these yeasts serve as crucial indicators of ecosystem health and function and are excellent candidates for biotechnological and industrial applications. Collectively, this study not only expands our knowledge of the diversity and distribution of intertidal yeasts but also highlights their promising potential for biotechnological applications.

The dominant mechanisms of nutrient cycling in high-dam reservoirs: retention, transport or transformation?

Abstract High-dam reservoirs can significantly affect nutrient cycling processes across the globe. However, the research community now has two contradictive views (i.e. retention versus transformation) about the impact of high-dam reservoirs on nutrient cycling due to incomplete information obtained from limited field samplings. To resolve this issue, we develop a physically-based, three-dimensional water quality model to examine the spatiotemporal distributions of biogenic elements (nitrogen and phosphorus) in high-dam reservoirs with high spatial and temporal details. We apply the model to the Xiaowan Reservoir, a representative high-dam reservoir in the Lancang River Basin. By scrutinizing the spatiotemporal distributions of biogenic elements across space and over time, we find a unique ‘retention-transformation-transportation’ process of nitrogen and phosphorus in the high-dam reservoir, with dominant transformation occurring in the water zone before the dam during non-flood period while dominant retention occurring in the middle part of a reservoir during flood period. We further find that transformations of biogenic elements are enhanced only in low-temperature and low-oxygen environments. Our findings show solid scientific basis to resolve the contradictive views about nutrient cycling mechanisms in high-dam reservoirs, and provide important policy implications for the operation of high-dam reservoirs to achieve improved water quality while maintaining clean energy supply.

Revealing the metabolic potential and environmental adaptation of nematophagous fungus, Purpureocillium lilacinum, derived from hadal sediment

The extreme environment shapes fungi in deep-sea sediments with novel metabolic capabilities. The ubiquity of fungi in deep-sea habitats supports their significant roles in these ecosystems. However, there is limited research on the metabolic activities and adaptive mechanisms of filamentous fungi in deep-sea ecosystems. In this study, we investigated the biological activities, including antibacterial, antitumor and nematicidal activity of Purpureocillium lilacinum FDZ8Y1, isolated from sediments of the Mariana Trench. A key feature of P. lilacinum FDZ8Y1 was its tolerance to high hydrostatic pressure (HHP), up to 110 MPa. We showed that HHP affected its vegetative growth, development, and production of secondary metabolites, indicating the potential for discovering novel natural products from hadal fungi. Whole-genome sequencing of P. lilacinum FDZ8Y1 revealed the metabolic potential of this piezotolerant fungus in carbon (carbohydrate metabolism), nitrogen (assimilatory nitrate reduction and protein degradation) and sulfur cycling processes (assimilatory sulfate reduction). Transcriptomic analysis under elevated HHP showed that P. lilacinum FDZ8Y1 may activate several metabolic pathways and stress proteins to cope with HHP, including fatty acid metabolism, the antioxidant defense system, the biosynthetic pathway for secondary metabolites, extracellular enzymes and membrane transporters. This study provides valuable insights into the metabolic potential and adaptation mechanisms of hadal fungi to the challenging conditions of the hadal environment.

Physicochemical perturbation increases nitrous oxide production from denitrification in soils and sediments

Abstract. Atmospheric concentrations of nitrous oxide (N2O), a potent greenhouse gas that is also responsible for significant stratospheric ozone depletion, have increased in response to the intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Microbial denitrification in soils and sediments is a major source of N2O, produced as an intermediate during the reduction of oxidized forms of nitrogen to dinitrogen gas (N2). Substrate availability (nitrate and organic matter) and environmental factors such as oxygen levels, temperature, moisture, and pH influence rates of denitrification and N2O production. Here we describe the role of physicochemical perturbation (defined here as a change from the ambient environmental conditions) in influencing rates of denitrification and N2O production. Changes in salinity, temperature, moisture, pH, and zinc in agricultural soils induced a short-term perturbation response characterized by lower rates of total denitrification and higher rates of net N2O production. The ratio of N2O to total denitrification (N2O : DNF) increased strongly with physicochemical perturbation. A salinity press experiment on tidal freshwater marsh soils revealed that increased N2O production was likely driven by transcriptional inhibition of the nitrous oxide reductase (nos) gene and that the microbial community adapted to altered salinity over a relatively short time frame (within 1 month). Perturbation appeared to confer resilience to subsequent disturbance, and denitrifiers from an environment without salinity fluctuations (tidal freshwater estuarine sediments) demonstrated a stronger N2O perturbation response than denitrifiers from environments with more variable salinity (oligohaline and mesohaline estuarine sediments), suggesting that the denitrifying community from physicochemically stable environments may have a stronger perturbation response. These findings provide a framework for improving our understanding of the dynamic nature of N2O production in soils and sediments, in which changes in physical and/or chemical conditions initiate a short-term perturbation response that promotes N2O production that moderates over time and with subsequent physicochemical perturbation.

Ecological roles of nano-picoplankton in stratified waters of an embayment in the southern Benguela.

Nano-picoplankton are the dominant primary producers during the post-upwelling period in St Helena Bay, South Africa. Their dynamics on short time scales are not well understood and neither are the community composition, structure, and potential functionality of the surrounding microbiome. Samples were collected over five consecutive days in March 2018 from three depths (1 m, 25 m, 50 m) at a single sampling station in St Helena Bay. There was clear depth-differentiation between the surface and depth in both diversity and function throughout the sampling period for the archaea, bacteria and eukaryotes. Daily difference in eukaryote diversity, was more pronounced at 1 m and 25 m with increased abundances of Syndiniales and Bacillariophyta. Surface waters were dominated by photosynthetic and photoheterotrophic microorganisms, while samples at depth were linked to nitrogen cycling processes, with high abundances of nitrifiers and denitrifiers. Strong depth gradients found in the nutrient transporters for ammonia were good indicators of measured uptake rates. This study showed that nano-picoplankton dynamics were driven by light availability, nutrient concentrations, carbon biomass and oxygenation. The nano-picoplankton help sustain ecosystem functioning in St Helena Bay through their ecological roles, which emphasizes the need to monitor this size fraction of the plankton.

Targeted Electrocatalysis for High‐Performance Lithium–Sulfur Batteries

The intricate sulfur redox chemistry involves multiple electron transfers and complicated phase changes. Catalysts have been previously explored to overcome the kinetic barrier in lithium–sulfur batteries (LSBs). This work contributes to closing the knowledge gap and examines electrocatalysis for enhancing LSB kinetics. With a strong chemical affinity for polysulfides, the electrocatalyst enables efficient adsorption and accelerated electron transfer reactions. Resulting cells with catalyzed cathodes exhibit improved rate capability and excellent stability over 500 cycles with 91.9% capacity retention at C/3. In addition, cells were shown to perform at high rates up to 2C and at high sulfur loadings up to 6 mg cm−2. Various electrochemical, spectroscopic, and microscopic analyses provide insights into the mechanism for retaining high activity, coulombic efficiency, and capacity. This work delves into crucial processes identifying pivotal reaction steps during the cycling process at commercially relevant areal capacities and rates.

A Dual Effect Additive Modified Electrolyte Strategy to Improve the Electrochemical Performance of Zinc-Based Prussian Blue Analogs Energy Storage Device.

Prussian blue analogs (PBA) exhibit excellent potential for energy storage due to their unique three-dimensional open framework and abundant redox active sites. However, the dissolution of transition metal ions in water can compromise the structural integrity of PBAs, leading to significant issues such as low cycle life and capacity decay. To address these challenges, we proposed a dual-effect additive-modified electrolyte method to alleviate such issues, introducing sodium ferrocyanide (Na4Fe(CN)6) into aqueous alkaline electrolytes. It could not only capture Zn2+ dissolved on the surface of Na1.86Zn1.46[Fe(CN)6]0.87 (ZnHCF) electrode material during the cycling process but also conduct redox reactions on the electrode surface to provide additional capacitance. Through experiments and molecular simulation calculations, it showed that Na4Fe(CN)6 can restrict the movement of Zn dissolution into the electrolyte on the electrode surface. Based on this, an asymmetric supercapacitor based on ZnHCF//activated carbon was assembled with a modified electrolyte. The assembled supercapacitor displayed a specific capacitance of 1,329.65 mF cm-2, a power density of 2,900 mW cm-2, and an energy density of 388.28 mW h cm-2. This study provides a new idea for the design and construction of stable and efficient PBA energy storage materials by inhibiting the leaching of transition metals in PBA.

Electrochemical Properties of MIL‐100(Fe) Derived Double‐Shell Coating Anode Materials for Lithium‐Ion Battery

AbstractFe‐based anode materials with a high specific capacity, non‐toxic and abundant resources are among the ideal anode candidates for the new generation of LIBs. But their significant bulk effect causes the problems of the broken electrode structure and short cycle life that seriously hinder their practical applications. Herein, we prepared the core‐shell structure Fe3O4@C@SiO2 for the anode of LIBs by MIL‐101(Fe) derivatization using the solvent thermal method combined with the hydrolytic coating method. The porous carbon layer generated in situ by MOF pyrolysis, together with the coating of the SiO2 shell, can mitigate the volume expansion of ferric tetroxide during the cycling process. With these structural advantages, the Fe3O4@C@SiO2 anode preserves excellent performance with a specific capacity of 716 mAh/g for the 300 cycles at 1 A/g and 428 mAh/g after 2000 cycles as the density is up to 5 A/g. This work presents a promising approach for preparing SiO2‐coated core‐shell structured TMOs composite anodes.

High-performance flexible CoFe2O4/N-doped carbon nanofiber composite anode materials for sodium-ion batteries

Graphite is traditionally used as an anode material but is unsuitable for use in sodium-ion batteries because it has a low specific capacity and poor safety characteristics, it is therefore necessary to develop alternative anode materials. Flexible CoFe2O4 nanoparticle/N-doped carbon nanofiber films were prepared by electrospinning and calcination. The advantages of this process included inexpensive starting materials, easy preparation, and suitability for commercialization. The inherent shortcomings of CoFe2O4, such as poor electronic conductivity and large changes in volume, were mitigated via elemental doping and the formation of composites with high-quality carbon materials. Nitrogen-doped carbon nanofibers with large specific surface areas and superior mechanical properties were used as the supporting skeleton of the material. These nanofibers limited the volume expansion of CoFe2O4 throughout the cycling process and increased the ion diffusion velocity in the material. The optimal integration of nanoscale CoFe2O4 particles, which possess a higher theoretical specific capacity, with a nitrogen-doped carbon nanofiber conductive framework featuring a crosslinked three-dimensional structure facilitated the infiltration of the electrolyte into the electrode. This integration reduced the diffusion distance of sodium ions and effectively reduced the volume expansion of the material, as well as damage to the material during the electrochemical reaction. After 200 cycles at a current density of 0.1 A g−1, it provided a high sodium storage capacity of 365.7 mA h g−1. The capacity was maintained at 176.3 mA h g−1 even at a high current density of 2 A g−1. Exhibits good cycle stability.

Wild Ungulates and Cattle Have Different Effects on Litter Decomposition as Revealed by Fecal Addition in a Northeast Asian Temperate Forest.

Litter decomposition is critical for maintaining productivity and nutrient cycling in forest ecosystems. Large herbivores play an essential role in determining the processes of nutrient cycling. Asian temperate forests are becoming degraded and fragmented by the widespread intensification of anthropogenic activities, including excessive livestock grazing. However, the effects of livestock grazing and wild ungulates on forest litter decomposition remain less explored. In this study, we used a litterbag experiment to investigate the effects of the addition of cattle (Bos taurus) and sika deer (Cervus nippon) feces on litter decomposition. The study was conducted in Northeast China from July 2022 to October 2023. We found that the addition of deer feces significantly reduced litter decomposition, but the addition of cattle feces greatly increased litter decomposition. The presence of cattle and deer excrement significantly accelerated the release of C after 1 year of litter decomposition. Compared with the results of the control group (no addition of feces), the addition of cattle and sika deer feces increased C release by 37.45% and 22.69%, respectively. Fecal addition increased the release of N; however, for the three treatment groups, the maximum accumulation of N occurred in the middle of litter decomposition, which may have been due to the initial chemical quality of the leaves and snow melt as well as nutrient limitations at the sites. Compared with the results of the control group, P release in the feces of cattle increased by 4.35%, but P release in the feces of deer decreased by 27.55%. This work highlights that feces deposition by large herbivores (e.g., wild or domestic) in the forest has nonequivalent effects on litter decomposition. Such effects may further alter the nutrient cycling in temperate forest ecosystems, with far-reaching effects on the ecosystem that deserve closer attention. We suggest that conservation managers should seek evidence-based interventions to optimize livestock use of forest habitats shared with wildlife.

Nanofluid channels mitigated Zn2+ concentration polarization prolonged over 30 times lifespan for reversible zinc anodes

Despite interfacial engineering protects zinc anode from electrolyte corrosion, the suppressed kinetics process on the anode surface/interface circumscribes their cyclic stability, especially dendritic growth induced by ion concentration gradients. Here, the zinophilic nanofluid channels (ZNC) protective layer on zinc surface are designed for the rapid Zn2+ transport kinetic in the reversible cycling process. The ZNC demonstrates high separation pressure between ions and the channel surface due to the capillary effect, allowing Zn2+ to quickly migrate along the channel wall (Zn2+ transference numbers up to 0.72). Therefore, the unique channel modules alleviate concentration polarization from rapid Zn2+ consumption and maintain uniform deposition of Zn ions. Consequently, The ZNC protective layer anode exhibits significantly improved cycle life by more than 30 times (over 4000 h at 1 mA cm−2) that of bare Zn. The full battery exhibits stable cycling performance with excellent capacity retention (∼100%) after 5000 cycles. Our work provides innovative insights into the role of nanofluids in improving the stability of zinc anodes, offering enlightening perspectives for long-cycle life zinc-based batteries.

Anthropogenic activities affect the diverse autotrophic communities of coastal sediments

Coastal sediments are a critical domain for carbon sequestration and are profoundly impacted by human activities. Therefore, it is essential to understand the structure and components of benthic autotrophs that play a crucial role in carbon sequestration processes, as well as the influence of anthropogenic activities on their communities. This study utilized an urban estuary, an industrial sea bay, a maricultural sea region, and two mangrove coastlines within the coastal areas of Guangdong Province, China. The micro-benthos in these environments, including prokaryotes and eukaryotes, were identified through high-throughput sequencing of 16S rRNA and 18S rRNA genes. The findings show that the autotrophic composition was altered by the interactions of anthropogenic heavy metals (Cd and Zn) and micro-eukaryotes (protazoa, metazoa, and parasitic organisms). Industrial pollution reduced the abundance of both prokaryotic and eukaryotic autotrophs. Mangroves induced a substantial transformation in the sediment eukaryotic and prokaryotic composition, increasing the proportion of autotrophs, notably sulfur-oxidizing and iron-oxidizing bacteria and microalgae. This alteration suggests an increase in specific sulfur and iron cycling with simultaneous carbon sequestration within mangrove sediments. These results indicate that anthropogenic activities affect sediment carbon sequestration by altering autotrophic assemblages along coastlines, thereby inducing consequential shifts in overall elemental cycling processes.

Higher temperature accelerates carbon cycling in a temperate montane forest without decreasing soil carbon stocks

Global warming is expected to accelerate the cycling of soil organic carbon (SOC) and the assimilation of new carbon, but the net effect of those counteracting accelerations and their ultimate effects on SOC are still uncertain. This hinders the prediction of long-term changes in biospheric carbon stocks and SOC-climate feedbacks. Here, we studied the long-term effect of temperature on carbon cycling across a 3.2 °C altitudinal temperature gradient in a temperate forest ecosystem in New Zealand. Across the gradient, soil respiration rates increased with increasing temperature from 9.0 to 10.4 tC ha−1 yr−1, but SOC stocks down to 85 cm depth also tended to increase, from 154 to 176 tC ha−1, albeit non-significantly (P = 0.06). This system was able to maintain higher soil respiration rates at higher temperatures without reducing SOC because the higher respiration rates were sustained by higher litterfall rates. Aboveground litterfall increased from 1.8 to 2.4 tC ha−1 yr−1 and estimated belowground C inputs increased from 7.2 to 8.0 tC ha−1 yr−1 along the temperature gradient. These higher fluxes were associated with significantly (P < 0.05) increased biomass at higher temperatures. As a direct measure of the effect of temperature on carbon cycling processes, we also calculated the turnover rate of forest litter which increased about 1.4-fold across the temperature gradient. This study demonstrates that higher temperatures along the thermal gradient increased plant carbon inputs through enhanced gross primary production, which counteracted SOC losses through temperature-enhanced soil respiration. These results suggest that temperature sensitivities of both plant carbon inputs and SOC losses must be considered for predicting SOC-climate feedbacks.

A new control strategy of direct exergy balance for coal-fired power plants: Fundamentals and performance evaluation

In order to facilitate the increasing penetration of grid-connected renewable power, coal-fired power plants should operate more and more flexibly. Most of the-state-of-the-art control strategies, which are mainly based on the idea of direct energy balance, cannot perform well when coal-fired power plants change load with high load cycling ramp rate. To enhance the operational flexibility of coal-fired power plants, the control idea of the direct exergy balance is proposed in this study, which directly characterizes the work capacity balance between the boiler and the steam turbine. The new control strategy of direct exergy balance emphasizes the feedback of the deviation between the turbine exergy demand signal and the boiler exergy signal. Dynamic models of a reference power plant were developed and validated, and performances of control strategies based on direct energy balance and direct exergy balance were evaluated and compared. In the 50 %–75 % load cycling process of the reference power plant, the control strategy of direct exergy balance demonstrated markedly improvements in the load cycling ramp rate (29 % relatively), the load cycling comprehensive index Kp (39.4 %), and reduction in the maximum deviations (28.2 %), overshoots (59.8 %), and cumulative deviations (36.9 %) of the key thermal parameters. In conclusion, the control strategy of direct exergy balance significantly strengthens the control performance during rapid load cycling processes and attains a notable enhancement in operational flexibility and a slight improvement in energy efficiency of coal-fired power plant.