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Abstract Climate warming threatens global food security by exacerbating pressures on degraded soils under intensive crop production. Conservation agriculture is promoted as a sustainable solution that improves soil health and sustains crop yields in a changing climate, but these benefits may be affected by long-term warming. Here, we investigate the effects of conservation agriculture compared to conventional agriculture on 17 soil properties, microbial diversity and crop yields, during eight-years’ experimental warming. An overall positive effect of warming on soil health over time under conservation agriculture is characterized by linear increases in soil organic carbon and microbial biomass carbon. Warming-triggered shifts in microbial biomass carbon and fungal diversity (saprogen richness) are directly linked to a 9.3% increase in wheat yields over eight years, but only under conservation agriculture. Overall, conservation agriculture results in an average 21% increase in soil health and supports similar levels of crop production after long-term warming compared to conventional agriculture. Our work provides insights into the potential benefits of conservation agriculture for long-term sustainable food production because improved soil health improves resilience to the effects of climate warming.

This study proposes a hollow-core anti-resonant fiber with a hybrid nested cladding structure, aimed at achieving high birefringence, broad bandwidth, and low confinement loss. The proposed fiber has a three-layer nested ring structure in the x-direction and a parallel array of four holes in the y-direction. The anti-resonance effect of multi-layer nested tubes greatly reduces the confinement loss of the fiber, while high birefringence characteristics is achieved by using different thicknesses of the cladding tubes. The coupling of the two glass modes of hybrid nested tubes and the core mode broadens the bandwidth range of low-loss and high birefringence. The theoretical results indicate that the birefringence of the fiber can reach 1.06×10-4, the confinement loss is as low as 1.8 dB/km at 1550 nm, and show the excellent single-mode characteristics with the higher-order mode extinction ratio 5539. Moreover, the confinement loss is as low as 2.4 dB/km at 2550 nm, and the birefringence reaches 1.1×10-4. The structure achieves low confinement loss, high birefringence and single mode at 1.54 ∼ 1.67 µm and 2.25 ∼ 2.85 µm dual wavelength ranges, which is the widest bandwidth range among all reported polarization maintaining fibers.

Long period gratings, based on anti-resonant hollow core fibers (AR-HCFs), are fabricated using a high-frequency CO _2 laser pulse by carving periodic grooves. This device exhibits both axial strain and bending sensing characteristics. Benefiting from the low thermal sensitivity and radiation resistance characteristic of AR-HCFs, this grating can be utilized in extreme environments, particularly in the high-radiation environment, such as nuclear power plants and space shuttles. Additionally, due to the characteristics of AR-HCFs, including low latency, low dispersion, low nonlinearity, and high damage threshold, this device also serves for long-distance fiber communication and high-power laser pulse shaping.

Understanding the sensitivity of ecosystem respiration (ER) to increasing temperature is crucial to predict how the terrestrial carbon sink responds to a warming climate. The temperature sensitivity of ER may vary on a diurnal basis but is poorly understood due to the paucity of observational sites documenting real ER during daytime at a global scale. Here, we used an improved flux partitioning approach to estimate the apparent temperature sensitivity of ER during the daytime (E0,day) and nighttime (E0,night) derived from multiyear observations of 189 FLUXNET sites. Our results demonstrated that E0,night is significantly higher than E0,day across all biomes, with significant seasonal variations in the day–night discrepancy in the temperature sensitivity of ER (ΔE0 = E0,night/E0,day) except for evergreen broadleaf forest and savannas. Such seasonal variations in ΔE0 mainly result from the effect of temperature and the seasonal amplitude of NDVI. We predict that future warming will decrease ΔE0 due to the reduced E0,night by the end of the century in most regions. Moreover, we further find that disregarding the ΔE0 leads to an overestimation of annual ER by 10~80% globally. Thus, our study highlights that the divergent temperature dependencies between day- and nighttime ER should be incorporated into Earth system models to improve predictions of carbon–climate change feedback under future warming scenarios.

Abstract Introduction Forest restoration is an effective way to promote ecosystem functions and mitigate climate change. However, how forest restoration affect soil C:N:P stoichiometry and microbial biodiversity, as well as their linkage across contrasting forest types globally remains largely illusive. Materials and Methods Here we conducted a global meta‐analysis by synthesizing 121 published papers with 1649 observations to explore how forest restoration affect soil C:N:P stoichiometry and microbial biodiversity globally. Results Forest restoration significantly increased soil total carbon (C), nitrogen (N) and phosphorus (P) content, whereas having no significant impact on most microbial diversity indicator, except for an enhancement in bacterial operational taxonomic unit and fungal Simpson. Meanwhile, forest restoration effects on soil C:N:P stoichiometry varied with different forest types, with promoting more soil C and P in ectomycorrhizal than those in arbuscular mycorrhizal forests. Meanwhile, forest restoration induced changes in soil N and P were positively correlated with microbial Shannon index. More importantly, forest restoration effects on soil C:N:P stoichiometry and microbial biodiversity were regulated by climate factors such as mean annual temperature and mean annual precipitation. Conclusion Our results highlight the crucial role of forest restoration in decoupling the biogeochemical cycles of C, N and P through changes in microbial biodiversity. Therefore, incorporating the decouple effects of forest restoration on soil C:N:P stoichiometry into Earth system models may improve predictions of climate–forest feedbacks in the Anthropocene.

IntroductionSoil bacteria play a crucial role in the terrestrial nitrogen (N) cycle by fixing atmospheric N2, and this process is influenced by both biotic and abiotic factors. The diversity of N2-fixing bacteria (NFB) directly reflects the efficiency of soil N fixation, and the diversity of NFB in degraded alpine meadow soil may change with different N fertilizing levels and varied slopes. However, how N addition affects the diversity of NFB in degraded alpine meadows, and whether this influence varies with slope, remain poorly understood.MethodsWe conducted an N addition field experiment at three levels (2, 5, and 10 g N·m−2·a−1) to study the effects of N addition on soil NFB diversity on two different slopes in a degraded meadow on the Tibetan Plateau.ResultsThere were significant differences in the dominant bacterial species between the two slopes. The Chao1 index, species richness, and beta diversity of NFB did not differ significantly between slopes, but the Shannon index did. Interestingly, N addition had no effect on the diversity of NFB or the abundance of dominant bacteria. However, we did observe a significant change in some low-abundance NFB. The community composition and diversity of NFB were significantly positively correlated with slope and soil physicochemical properties (e.g., total potassium, pH, and total nitrogen).ConclusionsOur study highlights the variation in NFB communities among different slopes in degraded alpine meadows and their resilience to exogenous N addition. Our results also underscore the importance of considering the effects of micro-topography on soil microbial communities in future studies of alpine ecosystems.

Biomass allocation in plants is fundamental for understanding and predicting terrestrial carbon storage. Here, the authors conduct a meta-analysis showing that warming effect on plant root:shoot is influenced by precipitation and the type of mycorrhizal fungi associated.

A novel hollow-core antiresonant fiber with a Bragg structure is proposed. It is numerically simulated using a commercial finite element method, and optical properties of the fiber, such as mode field, confinement loss, and bend loss, are numerically analyzed. The proposed hollow-core antiresonant fiber has advantageous optical properties, such as ultralow confinement loss, large bandwidth, and low bend loss. The structural advantage of the hollow-core Bragg antiresonant fiber also facilitates the fabrication of long-distance hollow-core antiresonant fibers. Additionally, this fiber offers potential applications in long-distance communications, data transmission, and laser power delivery.

Multi-wavelength polarizers have many essential applications in optics, quantum communication, Q switch and relating research fields. However, polarizing waveband of the traditional polarizer is restricted in the structure of fibers, which results in finite polarizing wavelengths. In this work, a novel D-shaped microstructure fiber polarizer (DMFP) with metal grating was proposed. Utilizing the abundant harmonic vector characteristics on the surface of metal grating, the DMFP can realize the function of multi-band polarization filtering. Numerical results show that it can achieve three bands of polarization filtering in x-polarized mode from 350 nm to 1600 nm and the resonance wavelengths are periodically modulated by grating. In the meanwhile, by optimizing grating parameters, the number of bands of polarization filtering can be further increased, thus, it fulfills the effective adjustment of polarization filtering. It is promising that metal grating based DMFP has great potential values in the fields of optical filter, communication, and functional devices, etc.

With an increase in the volume of information exchange and perception, the demands for intelligent, miniaturized, and integrated optical devices for information acquisition are also increasing. As the core component of optical networks for transmitting information, further optimization of their structural characteristics to generate richer optical characteristics and apply them to information exchange and optical field control has become a key research hotspot. The introduction of chiral twist characteristics has led to new phenomena and applications in optical field transmission and the transformation of traditional optical fibers or microstructured optical fibers (MOF). Therefore, this review mainly begins with the principle of chiral optical fibers, introduces their preparation and latest application scenarios, and finally discusses their potential future development prospects.

Abstract Both biochar and nitrogen (N) addition have been proposed for enhancing plant productivity and increasing carbon (C) sequestration. Although numerous studies have been conducted to examine responses of soil greenhouse gas (GHG) fluxes to biochar or N addition, biochar is often co‐applied with N fertilizer and the interactive effects of the two factors still remain unclear. In this study, we performed a meta‐analysis of manipulative experiments with 267 two‐factor observations to quantify the main and interactive effects of biochar and N addition on soil GHG fluxes at a global scale. Our results showed that biochar addition significantly increased soil CO2 emission by 10.1%, but decreased N2O emission by 14.7%. Meanwhile, N addition increased both soil CO2 and N2O emissions by 11.6% and 288%, respectively. The combination of biochar and N addition also exhibited significant positive effect on CO2 (+18.0%) and N2O (+148%) emissions, but there were non‐significant changes in CH4 fluxes. Consequently, antagonistic interaction between biochar and N addition was observed in soil GHG fluxes and their global warming potential (GWP), except for CH4 uptake showing an additive interaction. This synthesis highlights the importance of the interactive effects between biochar and N addition, providing a quantitative basis to develop sustainable strategies toward widespread application of biochar to preserve cropping system and mitigate climate change.

Summary: The ability to accurately and cost-friendly monitor heavy metals in environmental solutions such as drinking or tap water is of great significance to the human health. We report a twisted fiber-based sensing mechanism that can realize highly accurate detection of Cd2+ concentration in water solution. The basic design is a twisted single-core fiber simply coated with a propylene thiourea membrane that can absorb Cd2+. Due to the twisting effect, light in the core can scatter into the cladding, yielding optical coupling and interference. We experimentally prove that both positions and amplitudes of interference dips in the sample transmission spectrum can effectively and linearly response to the change of Cd2+ concentration at the level of 10−11 mol/L. With bimodal calibration, such sensor can realize accurate and real-time monitor in a stable and nontoxic way. These excellent characteristics indicate promising potential in the field of biochemical and integrated optical sensing.

Abstract The long‐term contribution of global forest restoration to support multiple dimensions of biodiversity and ecosystem function remains largely illusive across contrasting climates and forest types. This hampers the capacity to predict the future of forest rewilding under changing global climates. Here, 120 studies are synthesized across five continents, and it is found that forest restoration promotes multiple dimensions of biodiversity and ecosystem function such as soil fertility, plant biomass, microbial habitat, and carbon sequestration across contrasting climates and forest types. Based on global relationship between stand age and soil organic carbon stock, planting 350 million hectares of forest under the UN Bonn Challenge can sequester >30 Gt soil C in the surface 20 cm over the next century. However, these findings also indicate that predicted increases in temperature and reductions in precipitation can constrain the positive effects of forest rewilding on biodiversity and ecosystem function. Further, important tradeoffs are found in very old forests, with considerable disconnection between biodiversity and ecosystem function. Together, these findings provide evidence of the importance of the multidimensional rewilding of forests, suggesting that on‐going climatic changes may dampen the expectations of the positive effects of forest restoration on biodiversity and ecosystem function.

A Hollow-core Anti-resonant Fiber (ARF) has many advantages in device applications, such as low cladding density, low nonlinearity, high damage threshold, and excellent polarization characteristics by adjusting the structure and filling a metal. A method of on-line copper coating on the inner hole of hollow-core anti-resonant fiber cladding during drawing is proposed in this paper, and the related polarization characteristic of the ARF is studied. The theoretical and experimental results show that the ARF has good polarization characteristics after coating due to the coupling of copper film and core mode. Polarized light at 860 nm shows the best polarization characteristics. When the ARF is 1 mm, 1.5 mm, and 2 mm in length, its crosstalk is more than 20 dB which works well in communications applications. These characteristics indicate that the ARF coated copper film has a good application prospect in the field of polarization communication.

Mode-division multiplexing (MDM) can achieve ultra-high data capacity in optical fiber communication. Several impressive works on multicore fiber (MCF), multi-mode fiber, and few-mode multicore fiber have made significant achievements in MDM. However, none of the previous works can simultaneously maintain the transmission loss, chromatic dispersion (CD), and differential group delay (DGD) at a relatively low level. A nested multiple hollow-core anti-resonant fiber (NMH-ARF) has significant potential for applications in MDM. This study proposes a novel NMH-ARF with its structural design based on the traditional single-core nested anti-resonant fiber. We increased the number of nodes between capillaries. By changing the position of the nested tubes, several interconnected areas form when a single core is separated. We investigated the mode-coupling theory and transmission characteristics of this fiber. This fiber structure showed a low sensitivity to bending and achieved a super-low DGD and a super-low confinement loss (CL) at a wavelength of 1.55 µm while keeping CD relatively low.

To effectively improve the cutting quality of sapphire and optimize ultrafast picosecond laser cutting technology, this paper presents a new numerical simulation method and an experimental study of the ultrafast double-laser cutting of sapphire materials. The optimal cutting technology and the numerical simulation of the temperature field of the ultrafast picosecond laser cutting of sapphire were designed independently. The principle is based on double-laser-beam cutting using an ultrashort pulse and a CO2 beam; the ultrashort pulse is focused on the material through a laser filamentous cutting head and perforated, and it moves at a speed of up to 200 mm/s to form the desired cutting line. Then, a CO2 beam is used for heating, and the principle of heat bilges and cold shrink causes the rapid separation of products. Furthermore, an SEM tester was used to characterize and analyze the microstructure and properties of sapphire materials. A microscope was used to analyze the composition of the cutting micro-area and explore the general mechanism of laser cutting sapphire. The results showed that the proposed method greatly improves efficiency and precision; in addition, the chipping size of sapphire is less than 4 μm.

We present the first demonstration of an actively Q-switched orthogonally polarized dual-wavelength Nd:YLF/YVO4 Raman laser to our knowledge. The gain competition of the orthogonally polarized dual-wavelength fundamental laser at 1047 and 1053 nm was ultimately avoided by incorporating two Nd:YLF crystals into two laser resonators. By adjusting the gain or loss difference of two resonators, the pulse synchronization of the orthogonally polarized dual-wavelength Raman laser was realized. Benefitting from the efficient thermal stress and energy-transfer upconversion management of Nd:YLF crystal, a maximum dual-wavelength Raman output power of 4.5 W was obtained with M2

Abstract Deep-ultraviolet (UV) second-harmonics (SHs) have important applications in basic physics and applied sciences. However, it still remains challenging to generate deep-UV SHs especially in optical fibers. Here, for the first time, we experimentally demonstrate the deep-UV SH generations (SHGs) by combined degenerate four-wave mixing (FWM) and surface nonlinearity polarization in an in-house designed and fabricated air-silica photonic crystal fiber (PCF). When femtosecond pump pulses with average input power P av of 650 mW and center wavelength λ p of 810, 820, 830, and 840 nm are coupled into the normal dispersion region close to the zero-dispersion wavelength of the fundamental mode of the PCF, the anti-Stokes waves induced by degenerate FWM process are tunable from 669 to 612 nm. Then, they serve as the secondary pump, and deep-UV SHs are generated within the wavelength range of 334.5 to 306 nm as a result of surface nonlinearity polarization at the core-cladding interface of the PCF. The physical mechanism of the SHGs is confirmed by studying the dependences of the output power P SH of the SHs on the PCF length and time. Finally, we also establish a theoretical model to analyze the SHGs.

As a surface finishing technique for rapid remelting and re-solidification, laser polishing can effectively eliminate the asperities so as to approach the feature size. Nevertheless, the polished surface quality is significantly sensitive to the processing parameters, especially with respect to melt hydrodynamics. In this paper, a transient two-dimensional model was developed to demonstrate the molten flow behavior for different surface morphologies of the Ti6Al4V alloy. It is illustrated that the complex evolution of the melt hydrodynamics involving heat conduction, thermal convection, thermal radiation, melting and solidification during laser polishing. Results show that the uniformity of the distribution of surface peaks and valleys can improve the molten flow stability and obtain better smoothing effect. The high cooling rate of the molten pool resulting in a shortening of the molten lifetime, which prevents the peaks from being removed by capillary and thermocapillary forces. It is revealed that the mechanism of secondary roughness formation on polished surface. Moreover, the double spiral nest Marangoni convection extrudes the molten to the outsides. It results in the formation of expansion and depression, corresponding to nearby the starting position and at the edges of the polished surface. It is further found that the difference between the simulation and experimental depression depths is only about 2 μm. Correspondingly, the errors are approximately 8.3%, 14.3% and 13.3%, corresponding to Models 1, 2 and 3, respectively. The aforementioned results illustrated that the predicted surface profiles agree reasonably well with the experimentally measured surface height data.

A pure silica core photonic crystal fiber with multicoating layers for high refractive index (RI) sensing is proposed. Au is used as the active plasmonic material. Tantalum pentoxide is deposited on Au in order to prevent the oxidation and further enhance the evanescent field. The simulation was preformed through the full-vector finite element method (FEM), and the results show that the proposed fiber sensor can obtain the average wavelength sensitivity of 9180 nm/RIU with the analyte RI range of 1.40-1.44, corresponding to the resolution of 1.09 × 10-5 RIU. Moreover, the maximum amplitude sensitivity of 1739.26 RIU-1 with resolution of 5.75 × 10-6 RIU are also obtained. The designed sensor can be a potential candidate for microfluidic analyte detecting.

Dual-wavelength single polarizing filter has many important applications in the field of optical communication. Based on the principle of surface plasma resonance, a kind of dual-wavelength single polarizing filter with the broadband of low crosstalk was proposed in the paper by adopting good polarization characteristics of photonic crystal fiber. It could have single polarizing filtering in the dual-wavelength of 1310 and 1550 nm and the polarization direction of optical output is independent of the wavelength of incident light. The polarization direction of emergent light through filter can always keep the core mode in x-polarized direction (x-PCM) in a wide range of wavelength, which increases the difference of confinement loss of core mode in y-polarized direction (y-PCM) and x-PCM, and reduces mutual crosstalk. Meanwhile, the theoretical result also showed that the wavelength location and intensity of loss peak of polarizing mandrel are only affected by the air holes adjacent to fiber core and metal film and have little correlation with the structural parameters of other air holes, which ease the difficulty level of preparing filter based on photonic crystal fiber. Under certain structural parameters, the confinement loss of y-PCM could reach 265.04 dB/cm in 1310 nm and 230.5 dB/cm in 1550 nm. The half-width of confinement loss in the wavelength of 1310 nm is only 12 nm, while the loss of x-PCM is much smaller than that in y-PCM.

In this paper, we present a photonic crystal fiber (PCF) filter that it has the advantageous properties of narrow width and single-polarization through the principle of surface plasmon resonance (SPR) by a full-vector modal solver based on the finite element method. Gold nanowire is used as the SPR active metal and be filled into cladding air holes selectively. The proposed PCF can be used as a perfect polarization filter at 1.31 or 1.55 μm from y-polarized mode, respectively, if the appropriate sizes of the cladding air holes are selected. Only 13 nm that the full width at half maximum is able to achieve with one gold nanowire, and when the PCF is filled two gold nanowires, with a length of 1 mm of the designed PCF, the bandwidths with the crosstalk better than 30 dB can reach up to 235 nm, at the wavelength of 1.55 μm. The results indicate that the polarized light in one direction can be filtered out selectively by adjusting diameter of air holes and achieve filtering effect in communication bands.

A novel surface plasmon resonance (SPR) sensor based on ring-core microstructured optical fiber with silver film is presented in this paper. Field leakage from the ring core to the central metal film excites plasmon polaritons. Through numerical simulation with the finite-element method, we found that fundamental modes and one of second-order modes have strong interaction with surface plasma modes. Analyzing coupling characteristics, results show that high sensitivity using linear fitting and narrow full-width at half-maximum (FWHM) can both be acquired in these two modes, which contributes to the highest value of figure of merit reaching 2203. The proposed model with two air-hole rings is easy to fabricate in the real operation. Finally, influences of different metal and geometrical parameters on sensing performance are also discussed for optimization further.

In this paper, we propose a novel microstructure fiber with annular core for transmitting optical orbital angular momentum (OAM), and the OAM modes are calculated under different structure parameters of the fiber. Compared with the previous hollow step-index ring fiber, the proposed fiber brings higher refractive index contrast between the ring core and the cladding region by using only the single material of silica. The designed fiber can support more well-separated OAM modes with both thin and thick rings. Simulation results show that the novel microstructure ring fiber is promising to be applied in fiber-based OAM multiplexing in order to improve communication capacity.

A numerical investigation of a surface plasmon biosensor based on D-shaped microstructured optical fiber (MOF) with rectangular lattice is presented. A full-vector finite-element method is applied to analyze the resonance coupling properties. By adjusting the diameters of two large air holes, the proposed biosensor shows excellent performance. High sensitivity and narrow full-width at half-maximum (FWHM) can be achieved. In particular, the figure of merit can reach to 478.3RIU-1, which is to our knowledge the highest among the reported MOF sensors. In the last part, the influence of coating thickness on the sensing performance has been considered.

With the homemade solid-core silica-based photonic crystal fiber (PCF), we observe the generation of soliton and four-wave mixing (FWM) when the femtosecond pulse is pumped at 0.822 μm, belonging to the normal-dispersion regime. It is generally acknowledged that FWM is unrelated to third-order dispersion, whereas we use the fourth-order Runge-Kutta method to simulate the PCF properties by taking into account the third-order dispersion or not; the result we got is different from the conventional one. The numerical simulations are greatly consistent with the experiment results, and the FWM is dominated by negative fourth-order and negative sixth-order dispersion in the experiment. The main dynamic process is explained as the soliton, and the FWM generation can be induced by third-order dispersion. We indicate that low Raman threshold has played a very active role in this process, and we propose a conception of stimulated FWM effect in this paper.

Introduction: Soil bacteria play a crucial role in the terrestrial nitrogen (N) cycle by fixing atmospheric N2, and this process is influenced by both biotic and abiotic factors. The diversity of N2-fixing bacteria (NFB) directly reflects the efficiency of soil N fixation, and the diversity of NFB in degraded alpine meadow soil may change with different N fertilizing levels and varied slopes. However, how N addition affects the diversity of NFB in degraded alpine meadows, and whether this influence varies with slope, remain poorly understood. Methods: We conducted an N addition field experiment at three levels (2, 5, and 10 g N·m-2·a-1) to study the effects of N addition on soil NFB diversity on two different slopes in a degraded meadow on the Tibetan Plateau. Results: There were significant differences in the dominant bacterial species between the two slopes. The Chao1 index, species richness, and beta diversity of NFB did not differ significantly between slopes, but the Shannon index did. Interestingly, N addition had no effect on the diversity of NFB or the abundance of dominant bacteria. However, we did observe a significant change in some low-abundance NFB. The community composition and diversity of NFB were significantly positively correlated with slope and soil physicochemical properties (e.g., total potassium, pH, and total nitrogen). Conclusions: Our study highlights the variation in NFB communities among different slopes in degraded alpine meadows and their resilience to exogenous N addition. Our results also underscore the importance of considering the effects of micro-topography on soil microbial communities in future studies of alpine ecosystems. [ABSTRACT FROM AUTHOR]