Search

Nitrogen (N) availability limits plant growth and soil carbon (C) sequestration in N‐limited ecosystems, however, plant and soil C feedback on the free‐living nitrogen fixation (FLNF) process is poorly understood. Moreover, whether this feedback is influenced by initial N availability in leguminous and non‐leguminous forest soils has not been clarified. Here, we found that the addition of plant‐ and microbial‐derived C significantly enhanced soil nitrogenase activity (13∼28%) and that microbial‐derived C had a more positive impact. These positive effects were attributed to the direct C‐energy supply (0.49∼0.84) rather than variations in soil microbial activity (−0.01∼0.21) and substrate resources (−0.45∼0.27). Long‐term N addition did not inhibit FLNF. C addition promoted FLNF in soils of the two forests, but the response rate was higher in the leguminous forest soils. Our study reveals that increased soil C availability can drive FLNF in tropical forests, enhancing our understanding of the soil C‐N coupling mechanism. Plain Language Summary: Explicit consideration of controlling factors for free‐living nitrogen fixation (an important process of nitrogen biogeochemistry), is critical to understanding the response of ecosystems to environmental change. Our study reveals a previously overlooked but important process in which increased soil carbon availability exerts positive feedback on soil nitrogen inputs via free‐living nitrogen fixation. This insight enhances our understanding of soil carbon‐nitrogen coupling mechanisms and highlights an important nitrogen source in tropical forests based on increased vegetation and soil carbon sink conditions under global environmental change scenario. Key Points: Carbon (C) input affected free‐living nitrogen fixation (FLNF) more than nitrogen (N) application in tropical forest soilsBoth plant‐ and microbial‐derived C enhanced FLNF, but microbial‐derived C had a more positive impactC addition promoted FLNF in soils of the two forests, but the response rate was higher in the leguminous forest soils [ABSTRACT FROM AUTHOR]

Highly weathered lowland (sub)tropical forests are widely recognized as nitrogen (N)‐rich and phosphorus (P)‐poor, and the input of N and P affects soil carbon (C) cycling and storage in these ecosystems. Microbial residual C (MRC) plays a crucial role in regulating soil organic C (SOC) stability in forest soils. However, the effects of long‐term N and P addition on soil MRC across different soil layers remain unclear. This study conducted a 12‐year N and P addition experiment in two typical subtropical plantation forests dominated by Acacia auriculiformis and Eucalyptus urophylla trees, respectively. We measured plant C input (fine root biomass, fine root C, and litter C), microbial community structure, enzyme activity (C/N/P‐cycling enzymes), mineral properties, and MRC. Our results showed that continuous P addition reduced MRC in the subsoil (20–40 cm) of both plantations (A. auriculiformis: 28.44% and E. urophylla: 28.29%), whereas no significant changes occurred in the topsoil (0–20 cm). N addition decreased MRC in the subsoil of E. urophylla (25.44%), but had no significant effects on A. auriculiformis. Combined N and P addition reduced MRC (34.63%) in the subsoil of A. auriculiformis but not in that of E. urophylla. The factors regulating MRC varied across soil layers. In the topsoil (0–10 cm), plant C input (the relative contributions to the total variance was 20%, hereafter) and mineral protection (47.2%) were dominant factors. In the soil layer of 10–20 cm, both microbial characteristics (41.3%) and mineral protection (32.3%) had substantial effects, whereas the deeper layer (20–40 cm) was predominantly regulated by microbial characteristics (37.9%) and mineral protection (18.8%). Understanding differential drivers of MRC across soil depth, particularly in deeper soil layers, is crucial for accurately predicting the stability and storage of SOC and its responses to chronic N enrichment and/or increased P limitation in (sub)tropical forests. [ABSTRACT FROM AUTHOR]

In the doped hafnia(HfO2)-based films, crystallization annealing is indispensable in forming ferroelectric phases. In this paper, we investigate the annealing effects of TiN/Hf0.5Zr0.5O2/TiN metal-ferroelectric-metal (MFM) capacitors by comparing microwave annealing (MWA) and rapid thermal annealing (RTA) at the same wafer temperature of 500 °C. The twofold remanent polarization (2Pr) of the MWA device is 63 µC/cm2, surpassing that of the RTA device (40 µC/cm2). Furthermore, the wake-up effect is substantially inhibited in the MWA device. The orthorhombic crystalline phase is observed in the annealed HZO films in the MWA and RTA devices, with a reduced TiN and HZO interdiffusion in MWA devices. Moreover, the MFM capacitors subjected to MWA treatment exhibit a lower leakage current, indicating a decreased defect density. This investigation shows the potential of MWA for application in ferroelectric technology due to the improvement in remanent polarization, wake-up effect, and leakage current. [ABSTRACT FROM AUTHOR]

Sodium zirconium phosphate (labeled as NZP)-monazite-type (1-x)Sr0.5Zr2(PO4)3–xCePO4 (x = 0–1.0) composite ceramics, which were designed to simultaneously immobilize simulated fission nuclide Sr and variable valence actinide nuclide Ce, were in situ prepared by one-step microwave sintering technique. The feasibility of Sr/Ce co-immobilization was evaluated via an investigation on the phase evolution, microstructure, density, Vickers hardness, and chemical stability of the composite ceramics. The Ce valence state in the composite ceramics was further ascertained by X-ray photoelectron spectroscopy. It was shown that the Sr/Ce co-immobilized composite ceramics only consisted of Sr0.5Zr2(PO4)3 and CePO4 crystalline phases that were compatible well to each other. Sr and Ce were independently incorporated into Sr0.5Zr2(PO4)3 phase and CePO4 phase, respectively. The valence state of Ce in composite ceramics existed in trivalent state. And the existence of CePO4 phase caused the grain refinement and facilitated the densification of the composite ceramics. The composite samples all showed a highly uniform and dense microstructure, whose relative density was higher than 95% and Vickers hardness could attain 774 HV1. Importantly, the series of Sr0.5Zr2(PO4)3–CePO4 composite ceramics exhibited higher chemical stability than that of the monophase Sr0.5Zr2(PO4)3 or CePO4 ceramics, in which the normalized leaching rates of Sr and Ce were below 10−4 g·m−2·day−1 and 10−7 g·m−2·day−1 order of magnitude, respectively. The NZP-monazite-type composite ceramics has the potential to be a host for the disposal of high-level nuclear wastes containing multiple radionuclides. [ABSTRACT FROM AUTHOR]

The occurrence of the tropospheric ozone depletion events (ODEs) in the Antarctic can be influenced by the change in Total Ozone Column (TOC). In this study, we combined the observational data obtained from ground observation stations with two numerical models (TUV and KINAL), to figure out the relationship between the TOC change and the occurrence of ODEs in the Antarctic. A sensitivity analysis was also performed on the change in ozone and major bromine species (BrO, HOBr and HBr) to find out key photolysis reactions determining the impact on the occurrence of tropospheric ODEs brought by the change in TOC. From the analysis of the observational data and the numerical results, we suggested that the occurrence frequency of ODEs in the Antarctic seems negatively correlated with the variation of TOC. Moreover, major ODE accelerating reactions (i.e. photolysis of ozone, H2O2 and HCHO) and decelerating reactions (i.e. photolysis of BrO and HOBr), which heavily control the start of ODEs, were also identified. It was found that when TOC varies, the major ODE accelerating reactions speed up significantly, while major ODE decelerating reactions are only slightly affected, thus leading to the negative dependence of the ODE occurrence on the change in TOC. [ABSTRACT FROM AUTHOR]

In this letter, sub-10-nm air channel devices were fabricated with the aid of photolithography and focused ion beam (FIB) etching. Field emission (FE) properties of the device were measured under ambient conditions. The operation mechanism was discussed by means of current-voltage (I-V) curve fitting and energy band diagram analysis. On account of the extremely shrinking of nano-gap, record-high emission currents of 355.6 μA at 1 V were realized in air with a threshold voltage as low as 0.588 V. A cycle test of 200 times was also performed to verify and analyze the stability of the device. Importantly, the temporal response performance of the device was also measured. It demonstrated a high-speed and repeatable output waveform with a rise/fall time of ∼ 100 ns. This study demonstrates a practical nano-fabrication technology to fabricate sub-10-nm air channel devices with ultra-low operating voltage, which can be utilized as an electrical element in high-speed and low-power integrated circuits. [ABSTRACT FROM AUTHOR]

The nitrogen-doped TiO2 thin films are deposited on the glass substrate by using a direct-current (DC) magnetron sputtering technique. The film properties are analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. The results show that, under the same working pressure and other conditions, nitrogen doping promotes the phase transition from anatase to rutile. Also, on changing the nitrogen–oxygen ratio, nitrogen atoms enter the TiO2 lattice in different positions. When oxygen is abundant, nitrogen atoms will be presented in the interstitial positions; when oxygen is insufficient, nitrogen atoms enter the oxygen vacancies first, forming a substituted position. Finally, we find that, with the increase in nitrogen–oxygen ratio, the sample has a better response to visible light, attributed to the change in the energy band-gap. [ABSTRACT FROM AUTHOR]