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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.

To improve the dispersion of metals and to enhance the catalytic performance of SAPO-34 molecular sieves, the template-assisted method was applied to synthesize Co, Ni and Zn modified SAPO-34 molecular sieves by using palygorskite as silicon source and tetraethylammonium hydroxide as template. The metal modified SAPO-34 molecular sieves were characterized by XRD, SEM, XPS, N2-adsorption-desorption, NH3-TPD, FTIR, ICP-AES and TG. The N atoms of tetraethylammonium hydroxide exhibited the different forces to three metal ions, thus the acidity of the molecular sieves was further regulated. Compared with metal modified SAPO-34 molecular sieves prepared by impregnation, metal modified SAPO-34 molecular sieves prepared by template-assisted maintained higher surface area, bigger pore volume and better dispersion of metals. The catalytic performance of metal modified SAPO-34 molecular sieves prepared by template-assisted method in the reaction of methanol-to-olefins (MTO) was investigated in the fixed bed reactor. Under the reaction conditions that the reaction temperature was 400 °C, the reaction pressure was 0.1 MPa, the feed WHSV was 2.0 h−1 and the mass of catalyst was 0.5 g, Ni modified SAPO-34 molecular sieves exhibited great methanol conversion and high selectivity to light olefins. The selectivity of light olefins reached 95.7%.

Phosphorus promoted HZSM-5 zeolites (P-HZSM-5) were prepared by synthetic methods of incipient wetness impregnation and in situ synthesis, respectively. This was characterized by the means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller method (BET), thermogravimetry (TG), and NH3-TPD. The P-HZSM-5 zeolite prepared by incipient wetness impregnation has a large specific surface area and pore size, and the weak acidity is remarkably increased. The catalytic activity of P-HZSM-5 for the coupling transformation of methanol with 1-butene to propylene was investigated. Under the reaction conditions of temperature at 550 °C, pressure at 0.4 MPa, space velocity at 1800 mL/(gcat h), and mole ratio of CH3OH/C4H8 at 1:1, the conversion of C4H8 can reach to 75.8%, and the selectivity and yield of propylene are 42.2% and 31.9%, respectively.

Climate change has increased the frequency and intensity of droughts, with potential impacts on carbon (C) release from soil (i.e. soil respiration, Rs). Although numerous studies have investigated drought-induced changes in Rs, how roots and the soil microbial community regulate responses of Rs to drought remains unclear. We conducted a 4-year field experiment (2014–2017) with three treatments (i.e. 70% rainfall reduction, control and ambient) in a subtropical forest to examine effects of drought on Rs and its components [i.e. autotrophic (Ra) and heterotrophic respiration (Rh)] and explore the mechanisms underlying these effects. Drought significantly decreased Rs by 17% averaged over the 4 years, but it had no significant effect in the first experimental year. The decrease in Rs was mediated by soil fungi and fine root biomass. Fine root biomass was correlated negatively with Ra and Rs under drought, but positively in the control treatment. Furthermore, drought treatments increased physiological stress in the bacterial community. Structural equation model (SEM) analysis suggested that under drought conditions, microclimate affected Rs via its impact on fine root biomass and fungal biomass. Our results highlight the complex interactions between microclimate, roots and soil microbes in regulating Rs under drought in subtropical forest ecosystems. Incorporating these interactions into land surface models may improve predictions of climate change impacts on forest ecosystems. A free Plain Language Summary can be found within the Supporting Information of this article.

Plants and microbes are the primary drivers in affecting the formation and accrual of soil organic carbon (SOC) for natural ecosystems. However, experimental evidence elucidating their underlying mechanisms for SOC accumulation remains elusive. Here, we quantified plant and microbial contributions to SOC accrual in successional subtropical forests by measuring leaf-, root-, and microbial biomarkers, root and leaf litter inputs, and microbial C decomposition. The long-term monitoring results showed that SOC accumulated rapidly at the early-successional stage, but changed little at the mid- and late-successional stages. SOC accrual rate was positively correlated with fine-root production and microbial C turnover, but negatively with annual litterfall. Biomarker data exhibited that the rapid SOC accumulation was jointly driven by root- and microbe-derived C inputs from the early- to mid-successional stages. In contrast, aboveground litterfall considerably contributed to soil C accrual from the mid- to late-successional stages compared to belowground processes, although SOC accumulation is low. Our study revealed the importance of root production and microbial anabolism in SOC accrual at the early stages of forest succession. Incorporating these effects of belowground C inputs on SOC formation and accumulation into earth system models might improve model performance and projection of long-term soil C dynamics.

Root exudates determine plant’s ability to acquire nutrients through influencing plant’s interactions with soil microorganisms. Recent studies suggest that plant’s associations with beneficial soil microorganisms explain variation in root exudation as plants opt to minimize the exudation cost through such symbiosis. Yet, we have a poor understanding of whether plants change their exudation rates through mycorrhizal symbiosis in soil environments with varying resource availability. Here, we report the effects of plant-mycorrhizal symbiosis on root exudation rates across a gradient of soil phosphorous (P) availability from a field experiment in subtropical forests. Root exudation rates were higher in plants partnering with arbuscular mycorrhizal fungi than those with ectomycorrhizal fungi, but this difference disappeared in soils with high P. Specific root surface area, specific root length and fine root vitality explained high root exudation in P-limited soils. These findings demonstrate that mycorrhizal symbiosis and root functional traits collectively determine the variation in root exudation in Plimited environments.

Dissolved organic carbon (DOC) is one of the most important components in the global carbon cycle, which is largely influenced by climate and plant traits. Although previous studies have examined the impacts of climatic factors (e.g., mean annual temperature (MAT) and precipitation (MAP)) or plant traits (e.g., leaf area index, leaf nitrogen) on DOC, the relative importance of climate and plant traits on DOC flux remains unclear on a global scale. In this study, we compiled 153 pairs of DOC observational data from 84 forest sites to explore the relative importance of climate and plant traits on DOC flux with a linear mixed model, variance partitioning, and random forest approaches. Our results showed that DOC fluxes from throughfall and the litter layer were higher in broadleaved forests than those in coniferous forests. Throughfall-DOC flux increased significantly with MAT and MAP in coniferous forests, but that from the litter layer showed no significant correlations with climate factors. In broadleaved forests, throughfall-DOC flux increased with potential evapotranspiration (PET), while that from the litter layer was positively correlated with MAT. Meanwhile, throughfall-DOC flux had negative relationships with specific leaf area (SLA), leaf nitrogen content (LN), and leaf phosphorus content (LP) in broadleaved forests, but it showed a positive correlation with SLA in coniferous forests. Litter-layer-DOC flux increased with LN in broadleaved forests, but this correlation was the opposite in coniferous forests. Using the variance partitioning approach, plant traits contributed to 29.0% and 76.4% of the variation of DOC from throughfall and litter layer, respectively, whereas climate only explained 19.1% and 8.3%, respectively. These results indicate that there is a more important contribution by plant traits than by climate in driving the spatial variability of global forest DOC flux, which may help enhance forest management as a terrestrial carbon sink in the future. Our findings suggest the necessity of incorporating plant traits into land surface models for improving predictions regarding the forest carbon cycle.

Roots and their rhizosphere considerably influence soil structure by regulating soil aggregate formation and stabilization. This study aimed to examine the rhizosphere effects on soil aggregation and explore potential mechanisms along secondary forest successions. Effects of roots and their rhizosphere on soil aggregation in two subtropical secondary forest successions were examined by separating soils into rhizosphere and bulk soils. Soil aggregate mean weight diameter (MWD), soil organic carbon (SOC), soil nutrients, and fine-root traits were simultaneously measured. Soil aggregate MWD increased significantly in the bulk soils along secondary forest successions, but did not differ in the rhizosphere soils. Rhizosphere effects on soil aggregate MWD (i.e., root-induced differences between the rhizosphere and bulk soils) were thus significantly higher at the early-successional stage of subtropical forest with low soil fertility than those at the late stages with high fertility. Rhizosphere significantly increased SOC and soil total nitrogen (TN) throughout the entire secondary forest successions, which was nonlinearly correlated with soil aggregate MWD. Principal components regression analysis showed that SOC was the primary abiotic factor and positively correlated with soil aggregate MWD. As for biotic factors, fine-root length density and N concentration were two important root traits having significant effects on soil aggregate stability. An improved conceptual framework was developed to advance our understanding of soil aggregation and rhizosphere effects, highlighting the roles of soil fertility (i.e., SOC and available nutrients), root traits, and forest age in driving soil aggregation. Impacts of root-derived organic compounds inputs to rhizosphere on soil aggregation were stronger at the early-successional stage of subtropical forest than those at the late stages. This succession-specific pattern in rhizosphere effects largely resulted from the nonlinear relationships between soil aggregate MWD and SOC concentration with a plateau at high SOC. Incorporating the SOC-dependent rhizosphere effects on biogeochemical cycle into Earth system models might improve the prediction of forest soil C dynamics.

Void defects seriously threaten the overall force of the Sandwich-structured immersed tunnel (SSIT). Accurately identifying the location and evaluating the severity of the void defect through non-destructive testing methods to determine the overall structural health status can provide meaningful information for the grouting reinforcement repair of the immersed tunnel structure. This research has developed a method to identify void defects in SSIT by combining impact elastic wave technology with machine learning algorithms. Eleven eigenvalues including the waveform characteristics, frequency spectrum characteristics and structural location attributes of the impulse response waveform were integrated, and the different characteristics of the void defect area and the dense area were analyzed. Based on the full-size model experimental data, a sample database was established for model training and verification. The average accuracy of void-defect identification was 90.83%. The results show that this method has great potential for the detection and evaluation of void defects in SSIT structures.

Gypsum has been applied as a natural fertilizer and soil amendment for centuries in agriculture for providing crop nutrients such as Ca and S, and for improving soil physical properties. Recently, gypsum has been tested for sequestrating CO2 from the air and for capturing soluble phosphates in the soil, through formation of insoluble calcium phosphates and carbonates. However, the environmental factors controlling these sequestration processes have not been systemically studied. Here, we calculate optimal conditions of sequestration using chemical equilibrium modeling. Our results show that CO2 carbonation is effective at pH higher than 8.5 at atmospheric concentration. The removal of P is higher than 80 % for pH higher than 6.4, when Ca and P are at stoichiometric ratio. Also, placement of gypsum in subsoil is more effective for CO2 capture than applying it on soil surface since soil pores often contain higher concentrations of CO2 due to the soil respiration process. Overall, increases in medium pH, gypsum application rate, or CO2 partial pressure can increase the effectiveness of the amendment.

Nitrogen (N) exerts strong effects on litter decomposition through altering microbial abundance and community composition. However, the effect of N addition on plant–soil interactions such as home-field advantage (HFA: enhanced decomposition at a home environment compared to a guest environment) in relation to litter decomposition remains unclear. To fill this knowledge gap, we conducted a reciprocal litter transplant plus N addition experiment in Mytilaria laosensis and Cunninghamia lanceolata plantations for two years in subtropical China where anthropogenic N input is amongst the highest in the world. We found positive HFA effects (in which the calculation incorporates litter of both species) with litter mass loss 11.2% faster at home than in the guest environment in the N addition (50 kg N ha−1 yr−1) treatment, but no significant HFA effects were found in the control treatment. The magnitude of the HFA effect on carbon (C) release increased with N addition, while that on N release decreased. The HFA effects on phosphorus, potassium, calcium, sodium, and magnesium release were positive overall, but varied through time and the magnitude of the effects were different among elements. The greater HFA effects in the N addition treatment were associated with greater differences in microbial biomass and community composition between home and guest environments than in the control treatment. Our results indicate that anthropogenic N enrichment could lead to enhanced HFA effects, through modification of microbial communities, and thereby affect C sequestration and N cycling in subtropical forests.

Development and application of new types of fertilizers using innovative nanotechnology are one of the potentially effective options of significantly enhancing the global agricultural productions needed to meet the future demands of the growing population. Indeed, the review of available literature indicates that some engineered nanomaterials can enhance plant-growth in certain concentration ranges and could be used as nanofertilizers in agriculture to increase agronomic yields of crops and/or minimize environmental pollution. This article summarizes this type of nanomaterials under four categories: macronutrient nanofertilizers, micronutrient nanofertilizers, nutrient-loaded nanofertilizers, and plant-growth-enhancing nanomaterials. Each category is discussed respectively with reference to nanomaterials' chemical composition, particle size, concentrations applied, benefited plant species, plant incubation methods, and plant-growth enhancement aspects and the rates. The importance, research directions, and research requirements of each nanofertilizer category for achieving sustainable agriculture are also specifically examined. Finally, this review suggests that development of N and P macronutrient nanofertilizers is a high research and development priority both for food production and environmental protection.

Nano-sized apatite particles (nAP) synthesized with carboxymethyl cellulose (CMC) have shown great application potentials in in situ heavy metal remediation. However, differences in CMC’s properties effects on the size of nAP produced are not well understood. In this paper, two types of CMC, with respective molecular weights (MW) of ∼120000 and ∼240000 Dalton or respective polymerization degrees of 500 (CMC-500) and 1050 (CMC-1050), were studied in a concentration range of 0.05%–0.5% (w/w) for nAP synthesis. Morphology of the particles was characterized with transmission electron microscopy (TEM). Results showed that 0.05% CMC-500 solution gave an average particle size of 148.7±134.9 nm, 0.25% CMC-500 solution produced particles of 21.8±20.4 nm, and, 0.5% CMC-500 solution contained particles of 15.8±7.7 nm. In comparison, 0.05% CMC-1050 solution produced nanoparticles of 6.8±3.2 nm, 0.25% CMC-1050 produced smaller nAP of 4.3±3.2 nm, and 0.5% CMC-1050 synthesized the smallest nanoparticles in this study, with an average diameter of 3.0±2.1 nm. Chemical composition of the products was identified with X-ray diffraction (XRD) as pure hydroxyapatite. Interactions between nAP and CMC were discussed with help of attenuated total reflection Fourier transform infrared (ATRFTIR) spectroscopic data. This study showed that CMC at higher concentration as well as higher MW facilitated to produce finer nanoparticles, showing that nAP size could be manipulated by selecting appropriate CMC MW and/or applying appropriate CMC concentration.

Low concentrations of aqueous hydrogen sulfide (H2S) can stimulate growth of some crops. However, it is not clear whether H2S provides crops with only sulfur and whether other sulfur compounds have similar beneficial effects. Therefore, impacts of solutions of sodium sulfate (Na2SO4), sodium sulfite (Na2SO3), sodium sulfide (Na2S), ferrous sulfide (FeS), and H2S at 0.01–1 mM were assessed on 5-day lettuce seed germination. Results showed that 0.01 mM H2S solution significantly increased lettuce shoot elongation by 40 percent (to 43.6 mm from 31.0 mm in the control), whereas 0.1 mM increased elongation by 24 percent to 38.5 mm. Only a slight 10 percent increase was observed in 0.1 mM Na2SO4, suggesting that ameliorative impact of H2S on plant growth was not a result of providing sulfur nutrient. Other sulfur solutions, however, inhibited lettuce germination and elongation to varying extents, hinting that H2S might work as a signal molecule in regulating plant cellular activities.

Phosphate compounds and the related materials are effective agents for in situ immobilization of heavy metals in contaminated soils. Problems associated with using these phosphate materials include difficulties in delivering the solid phosphate minerals to the deep contaminated zones or risks of eutrophication with applying soluble phosphates. Therefore, a new class of apatite nanoparticles was synthesized using carboxymethyl cellulose as a stabilizer in order to increase the dispersion rate of phosphate in soils but without introducing significant amount of soluble phosphate into the environment. The product was confirmed by XRD as chlorapatite (Ca 5 (PO 4 ) 3 Cl) with poor crystallinity. TEM and SEM revealed that the particles were spherical or irregular in shape with sizes spanning from a few nm to around 200 nm. FTIR spectra suggested that Ca(II) cations formed outer-sphere bonds with carboxyl and hydroxyl groups in cellulose molecules, thus inhibiting further agglomeration of the particles. Dry combustion data supported a formula of [C 6 H 7 O 2 (OH) 2 OCH 2 COOCa 5 (PO 4 ) 3 Cl] n for the nano-apatite composite. Laboratory tests showed that the nanoparticles could effectively decrease the TCLP-leachable Pb fraction in a Pb-contaminated soil from 66% to 10% after one-month amendment with a ratio of 2 mL solution to 1 g soil and the resultant Pb content in the TCLP solution was reduced to 12 from 94 mg L −1 . When the amendment ratio was increased by 5 times, the leachable Pb was further reduced to 3.8 mg L −1 with only about 3% of the soil Pb leachable. The soil sample, containing an average of 2.7 × 10 3 mg Pb kg −1 , was taken from a shooting-range in Southern USA.

This paper reports the three-point bending fatigue behavior of 3-D carbon/epoxy braided composite in experimental and finite element analyses (FEAs) approaches. In the experimental approach, the stiffness degradation and maximum deflection curves were obtained to illustrate the relationship between applied stress levels and number of cycles to failure. In FEA approach, a user-defined material subroutine UMAT which characterizes the stiffness matrix and fatigue damage evolution of the 3-D braided composite was developed. It was incorporated with a finite element code ABAQUS/Standard to calculate the stiffness degradation and maximum deflection of the 3-D braided composite during each loading cycle. From the comparisons between experimental and FEA results, good agreements prove the validity of the unit cell model and the subroutine UMAT.

Rheology of slurry significantly influenced the grindability, fine grinding performance and energy consumption of industrial minerals in wet grinding. The solid concentration, particle size, temperature and the dispersant, which affected the rheological characteristics of pyrite slurry and the biooxidation process were investigated in this study. This research aimed at the wet grinding process improved by the control of slurry rheology and getting a biocompatible dispersant. The results revealed that the viscosity increased with the solid concentration, which was in agreement with the Chong model. There was a critical concentration (40 wt.%) that led to the flow behavior of slurry transformed from Newtonian fluids to shear-thinning non-Newtonian fluids which fitted to the Casson model. It was also found that the apparent viscosity of slurry increased with the decrease of the particle size and the temperature at high solid concentration. Sodium Hexametaphosphate (SH) was selected experimentally as an effective dispersant for the mineral slurry. The appropriate concentration of SH was also determined at the range from 0.005 wt.% to 0.05 wt.%. The addition of dispersants could reduce the viscosity and yield stress, increase the zeta potential ( ζ ) of suspension pronouncedly. No negative effects on the growth rate of microorganisms and the pyrite biooxidation were observed. Therefore, dispersant separation and recovery process could be avoided.

UHF RFID reader transceiver for Chinese local standard (840-845 MHz and 920-925 MHz), in concord with the protocols of EPC Class-1 Gen-2 and ISO/IEC 18000-6C, is presented. A highly linear RF front-end with low flicker noise, an on-chip self-jammer cancellation (SC) circuit with fast time-varying cut-off frequency and a DC-offset cancellation (DCOC) circuit are proposed to deal with the large self-jammer in the receiver. In the presence of 22 dBm PA output power, the receiver achieves a sensitivity of -79 dBm including the 15 dB loss of the directional coupler. A CMOS class-AB PA is integrated in the transmitter, with 22 dBm output power and 35% PAE. The spectrum mask achieves ACPR1 of -45 dBc and ACPR2 of -60 dBc . A sigma-delta fractional-N PLL with a single LC VCO is also implemented for good phase noise (-126 dBc/Hz @ 1 MHz offset) and high frequency resolution within 1 kHz. This single-chip is fabricated in a 0.18 standard CMOS process. It occupies a silicon area of 13.5 mm2 and dissipates 203 mW from a 1.8 V supply voltage when transmitting 7.5 dBm output power.

A pilot-scale study and field measurements at commercial ponds were conducted to investigate the environmental fate of copper (Cu) applied as an algaecide in commercial catfish ponds. In the pilot study, a total of 774 g Cu(II) was applied to an experimental catfish pond over a period of 16 summer weeks. More than 90% of Cu applied became associated with suspended sediment particles within a few minutes of addition, and then nearly all Cu applied was transferred to the sediment phase within about 2 days. At the end of the study, the peak Cu content in the sediment increased from an initial concentration of 25∼35 mg kg−1 to about 200 mg kg−1, and the applied Cu was able to reach a sediment depth of about 16 cm. Meanwhile, Cu concentration in the catfish body decreased from 12.7 ± 2.81 mg kg−1 to 6.15 ± 2.54 mg kg−1. Copper mass balance indicated that virtually all Cu applied was retained in the sediment. Only 0.01% of the total Cu applied was taken up by fish and 0.1% remained in pond water. Data from 3 commercial fishponds of different ages (1–25 years) and with different sediment types (acidic, neutral and calcareous) supported the pilot-scale observation. Both pilot-testing results and field measurements revealed that Cu is predominantly accumulated within the top sediment layer and barely reached the bottom soil regardless of the pond age and the type of the sediments. Field monitoring of groundwater quality suggested that the copper leaching into the groundwater surrounding the ponds was insignificant.