Enhancing Efficiency of Large-Area Wide-Bandgap Perovskite Solar Modules with Spontaneously Formed Self-Assembled Monolayer Interfaces.

Wide-bandgap (WBG) perovskites play a crucial role in perovskite-based tandem cells. Despite recent advances using self-assembled monolayers (SAMs) to facilitate efficiency breakthroughs, achieving precise control over the deposition of such ultrathin layers remains a significant challenge for large-scale fabrication of WBG perovskite and, consequently, for the tandem modules. To address these challenges, we propose a facile method that integrates MeO-2PACz and Me-4PACz in optimal proportions (Mixed SAMs) into the perovskite precursor solution, enabling the simultaneous codeposition of WBG perovskite and SAMs. This technique promotes the spontaneous formation of charge-selective contacts while reducing defect densities by coordinating phosphonic acid groups with the unbonded Pb2+ ions at the bottom interface. The resulting WBG perovskite solar cells (PSCs) demonstrated a power conversion efficiency of 19.31% for small-area devices (0.0585 cm2) and 17.63% for large-area modules (19.34 cm2), highlighting the potential of this codeposition strategy for fabricating high-performance, large-area WBG PSCs with enhanced reproducibility. These findings offer valuable insights for advancing WBG PSCs and the scalable fabrication of modules.

Quantitative Dual-Energy X-ray Imaging Based on K-Edge Absorption Difference.

Conventional flat panel X-ray imaging (FPXI) employs a single scintillator for X-ray conversion, which lacks energy spectrum information. The recent innovation of employing multilayer scintillators offers a route for multispectral X-ray imaging. However, the principles guiding optimal multilayer scintillator configuration selection and quantitative analysis models remain largely unexplored. Here, we propose to adopt the K-edge absorption coefficient as a key parameter for selecting tandem scintillator combinations and to utilize the coefficient matrix to calculate the absorption efficiency spectrum of the sample. Through a dual scintillator example comprising C4H12NMnCl3 and Cs3Cu2I5, we establish a streamlined quantitative framework for deducing X-ray spectra from scintillation spectra, with an average relative error of 6.28% between the calculated and measured sample absorption spectrum. This insight forms the foundation for our quantitative method to distinguish the material densities. Leveraging this tandem scintillator configuration, in conjunction with our analytical tools, we successfully demonstrate the inherent merits of dual-energy X-ray imaging for discerning materials with varied densities and thicknesses.

[Response of Organic Carbon Mineralization to Nitrogen Addition in Micro-aerobic and Anaerobic Layers of Paddy Soil].

In field conditions, a micro-aerobic layer with 1 cm thickness exists on the surface layer of paddy soil owing to the diffusion of dissolved oxygen via flooding water. However, the particularity of carbon and nitrogen transformation in this specific soil layer is not clear. A typical subtropical paddy soil was collected and incubated with13C-labelled rice straw for 100 days. The responses of exogenous fresh organic carbon(13C-rice straw) and original soil organic carbon mineralization to nitrogen fertilizer addition[(NH4)2SO4]in the micro-aerobic layer(0-1 cm) and anaerobic layer(1-5 cm) of paddy soil and their microbial processes were analyzed based on the analysis of 13C incorporation into phospholipid fatty acid(13C-PLFAs). Nitrogen addition promoted the total CO2 and 13C-CO2 emission from paddy soil by 11.4% and 12.3%, respectively. At the end of incubation, with the addition of nitrogen, the total soil organic carbon (SOC) and13C-recovery rate from rice straw in the anaerobic layer were 2.4% and 9.2% lower than those in the corresponding micro-aerobic layer, respectively. At the early stage(5 days), nitrogen addition increased the total microbial PLFAs in the anaerobic layer with a consistent response of bacterial and fungal PLFAs. However, there was no significant effect from nitrogen on microbial abundance in the micro-aerobic layer. Nitrogen addition had no significant impact on the abundance of total 13C-PLFAs in the micro-aerobic and anaerobic layers, but the abundance of 13C-PLFAs for bacteria and fungi in the micro-aerobic layer was decreased dramatically. At the late stage(100 days), the effect of nitrogen addition on microbial PLFAs was consistent with that at the early stage. The abundances of total, bacterial, and fungal 13C-PLFAs were remarkably increased in the anaerobic layer. However, the abundance of 13C-PLFAs in the micro-aerobic layer showed no significant response to nitrogen addition. During the incubation, the content of NH4+-N in the anaerobic soil layer was higher than that in the micro-aerobic soil layer. This indicates that nitrogen addition increased microbial activity in the anaerobic soil layer caused by the higher NH4+-N concentration, as majority of microorganisms preferred to use NH4+-N. Consequently, the microbial utilization and decomposition of organic carbon in the anaerobic soil layer were accelerated. By contrast, richer available N existed in the form of NO3--N in the micro-aerobic soil layer owing to the ammoxidation process. Thus, the shortage of NO3--N preference microorganisms in the paddy soil environment prohibited the microbial metabolism of organic carbon in the micro-aerobic layer. As a whole, nitrogen fertilization enhanced organic carbon loss via microbial mineralization in paddy soil with a weaker effect in the micro-aerobic layer than that in the anaerobic layer, indicating the limited microbial metabolic activity in the surface micro-aerobic layer could protect the organic carbon stabilization in paddy soil. This study emphasizes the heterogeneity of paddy soil and its significant particularity of carbon and nitrogen transformation in micro-aerobic layers. Consequently, this study has implications for optimizing the forms and method for the application of nitrogen fertilizer in paddy cropping systems.

Organic and Inorganic Metal Halide Tandem Scintillator for Dual-Energy Flat-Panel X-ray Imaging.

Traditional indirect flat-panel X-ray imaging (FPXI) uses inorganic scintillators with high-Z elements, which lack spectral information about X-ray photons and reflect only integrated X-ray intensity. To address this issue, we developed a stacked scintillator structure that combines organic and inorganic materials. This structure allows X-ray energies to be distinguished in a single shot by using a color or multispectral visible camera. However, the resolution of the resulting dual-energy image is primarily limited by the top scintillator layer. We inserted a layer of anodized aluminum oxide (AAO) between the double scintillators. This layer limits the lateral propagation of scintillation light, improves imaging resolution, and acts as a filter for X-rays. Our research demonstrates the advantages of stacked organic-inorganic scintillator structures for dual-energy X-ray imaging and provides novel and practical applications for relatively low-Z organic scintillators with high internal X-ray-to-light conversion efficiency.

[Effects of Organic Materials on Phosphorus Fractions and phoD-harboring Bacterial Community in Karst Soil].

Efficient utilization of organic materials based on the rich resources in the karst region can promote soil fertility. Microorganisms have a crucial influence on soil phosphorus availability. phoD is considered to be the encoding phosphatase gene that can reflect the hydrolysis of organophosphorus compounds for the soil bacterial community. Molecular analysis of the phoD-harboring bacterial gene provides insight into promoting soil phosphorus availability under different fertilization managements. However, the effects of organic materials on soil phosphorus fractions associated with phoD-harboring bacterial communities are poorly understood. This study comprehensively investigated the effects of organic materials on soil phosphorus availability and explored environmental drivers of phoD-harboring bacteria in the Karst region. Here, six treatments were designed in the field as follows:non-fertilized control (CK), inorganic fertilization (NPK), inorganic fertilization combined with straw (NPKS), inorganic fertilization combined with manure (NPKM), inorganic fertilization combined with sludge (NPKL), and inorganic fertilization combined with sugarcane ash (NPKA). The phoD-harboring bacterial community in Karst region soil was analyzed using high-throughput sequencing. The results showed that the content of total P (TP), Olsen-P, and Ca2-P increased with the years after organic material application, whereas the content of CaCl2-P first decreased and then increased. Compared to that under the CK treatment, organic material application, especially NPKL treatment, significantly increased soil total nitrogen (TN), TP, Olsen-P, CaCl2-P, and Ca2-P contents, followed by those in the NPKA and NPKM treatments. Correlation analysis showed that the contents of CaCl2-P, Ca2-P, and Olsen-P were significantly positively correlated with soil exchangeable calcium (Ca-ex) content. Redundancy analysis (RDA) showed that TN, Ca-ex, soil organic carbon (SOC), and total potassium (TK) contents were the key factors affecting soil P fractions. Using high-throughput sequencing, we found that only NPKS increased the richness of phoD-harboring bacteria compared to that under the control treatment. No significant difference was observed in the phoD-harboring bacterial community among all treatments. The RDA model selected the Ca-ex, TK, Olsen-P, pH, and SOC as the key environmental predictors for the phoD-harboring bacterial community. In summary, soil phosphorus availability can be improved through the input of organic materials and inorganic fertilizer combined with manure, sludge, and ash. These additions were suitable for nutrient management and sustainable development in farmland soil in the Karst region of Guangxi.

Multispectral Large-Panel X-ray Imaging Enabled by Stacked Metal Halide Scintillators.

Conventional energy-integration black-white X-ray imaging lacks the spectral information of X-ray photons. Although X-ray spectra (energy) can be distinguished by the photon-counting technique typically with CdZnTe detectors, it is very challenging to be applied to large-area flat-panel X-ray imaging (FPXI). Herein, multilayer stacked scintillators of different X-ray absorption capabilities and scintillation spectra are designed; in this scenario, the X-ray energy can be discriminated by detecting the emission spectra of each scintillator; therefore, multispectral X-ray imaging can be easily obtained by color or multispectral visible-light camera in a single shot of X-rays. To verify this idea, stacked multilayer scintillators based on several emerging metal halides are fabricated in a cost-effective and scalable solution process, and proof-of-concept multispectral (or multi-energy) FPXI are experimentally demonstrated. The dual-energy X-ray image of a "bone-muscle" model clearly shows the details that are invisible in conventional energy-integration FPXI. By stacking four layers of specifically designed multilayer scintillators with appropriate thicknesses, a prototype FPXI with four energy channels is realized, proving its extendibility to multispectral or even hyperspectral X-ray imaging. This study provides a facile and effective strategy to realize multispectral large-area flat-panel X-ray imaging.

[Characteristics of Microbial Utilization for Crop Residue-Derived C in Paddy and Upland Soils].

Two typical subtropical agricultural soils, a flooded paddy soil and its adjacent upland, were collected and then incubated with or without 13C-labeled crop residue (maize straw) for 40 days. During the incubation, the mineralization rate of the crop residue was monitored, and the 13C incorporated into fungal and bacterial phospholipid fatty acid (PLFA) was quantified. At the early stage (0.25-1 days), the mineralization rate of crop residue was faster in paddy soil than that in upland soil, whereas the opposite trend was observed from 2 to 20 days. At the late stage (21-40 days), the mineralization rate was similar in both soils. At the end of incubation, 11% of the total crop residue was mineralized in paddy soil, which was about half of that in upland soil (20%). Although paddy soil had a higher amount of microbial biomass (indicated by total PLFA), the total amounts of 13C-PLFA were comparable in both soils, and the enrichment ratio (proportion of 13C to total C in PLFA) was lower in paddy soil than that in upland soil. This indicated that the microbial community in paddy soil was less active in the uptake of crop residue C than that in upland soil. During the incubation, the residue-derived 13C was mainly distributed in bacterial PLFA (up to 86% of total 13C-PLFA, including 59% in gram-positive and 27% in gram-negative bacteria) in paddy soil, and up to 75% of total 13C-PLFA distributed in fungal PLFAs was in upland soil. Thus, bacteria dominated the utilization of crop residue in paddy soil versus fungi in upland soil. Compared with that in upland soil, the microbial activity was suppressed in the anaerobic condition caused by flooding in paddy soil, with a stronger inhibition of fungi than bacteria. Considering the discrepancies of life strategies and necromass turnover between bacteria and fungi, the different dominant microbial groups in the utilization of crop residue in water-logged and well-drained conditions could lead to the distinct accumulation and stabilization of microbial-derived organic matter in paddy and upland soils.

Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging.

X-ray detection, which plays an important role in medical and industrial fields, usually relies on inorganic scintillators to convert X-rays to visible photons; although several high-quantum-yield fluorescent molecules have been tested as scintillators, they are generally less efficient. High-energy radiation can ionize molecules and create secondary electrons and ions. As a result, a high fraction of triplet states is generated, which act as scintillation loss channels. Here we found that X-ray-induced triplet excitons can be exploited for emission through very rapid, thermally activated up-conversion. We report scintillators based on three thermally activated delayed fluorescence molecules with different emission bands, which showed significantly higher efficiency than conventional anthracene-based scintillators. X-ray imaging with 16.6 line pairs mm-1 resolution was also demonstrated. These results highlight the importance of efficient and prompt harvesting of triplet excitons for efficient X-ray scintillation and radiation detection.

Soil Microbial Resource Limitations and Community Assembly Along a Camellia oleifera Plantation Chronosequence.

Understanding soil microbial element limitation and its relation with the microbial community can help in elucidating the soil fertility status and improving nutrient management of planted forest ecosystems. The stand age of a planted forest determines the aboveground forest biomass and structure and underground microbial function and diversity. In this study, we investigated 30 plantations of Camellia oleifera distributed across the subtropical region of China that we classified into four stand ages (planted <9 years, 9-20 years, 21-60 years, and >60 years age). Enzymatic stoichiometry analysis showed that microbial metabolism in the forests was mainly limited by C and P. P limitation significantly decreased and C limitation slightly increased along the stand age gradient. The alpha diversity of the soil microbiota remained steady along stand age, while microbial communities gradually converged from scattered to clustered, which was accompanied by a decrease in network complexity. The soil bacterial community assembly shifted from stochastic to deterministic processes, which probably contributed to a decrease in soil pH along stand age. Our findings emphasize that the stand age regulated the soil microbial metabolism limitation and community assembly, which provides new insight into the improvement of C and P management in subtropical planted forest.

Flooding and straw returning regulates the partitioning of soil phosphorus fractions and phoD-harboring bacterial community in paddy soils.

Flooding and straw returning are effective agricultural practices in promoting phosphorus (P) availability in paddy soils. However, little is known about the effects of these practices and their interaction on the soil P pools and functional microbes responsible for soil P mobilization. Our 4-year paddy field experiment aimed to analyze the responses of soil P fractions and phoD-harboring bacterial communities in a double-rice cropping system to intermittent flooding (IF) and continuous flooding (CF), in plots with (+ S) and without (-S) straw return. Compared to IF, CF significantly increased soil citrate-P and marginally decreased the HCl-P fractions, suggesting that the stable inorganic P pools are transferred to labile inorganic P at lower redox potentials. Compared to the -S treatments, + S treatments significantly increased the labile organic fractions (enzyme-P). Correspondingly, a decreased soil total organic P concentration was observed in + S treatment. Additionally, + S treatment significantly increased the activity of acid phosphomonoesterase and alkaline phosphomonoesterase and the abundance of phoD-harboring bacteria. These results indicated that straw promoted organic P minimization to release orthophosphate. The diversity of the phoD-harboring bacteria and complexity of the co-occurrence network decreased under the CF + S treatment; however, all keystone species of the phoD-harboring bacteria were retained in this oxygen-deficient environment. This study highlights that irrigation regimes mediate the processes of inorganic P mobilization, while straw returns regulate the processes of organic P mineralization. Additionally, flooding could be a more effective agricultural practice than straw returning to promote soil P availability in paddy soils. KEY POINTS: •Soil P pools and phoD-harboring bacteria communities were assessed. •Straw return mainly affects the mineralization of organic P. •Continuous flooding mainly affects the mobilization of inorganic P.

Biochar protects hydrophilic dissolved organic matter against mineralization and enhances its microbial carbon use efficiency.

A combination of biochar with exogenous organic material in soils is often used in practical farmland management. The objective of this study was to determine how biochar affects organic matter decomposition by studying the decomposition of 13C-labelled hydrophilic (Hi-) and hydrophobic (Ho-) dissolved organic matter (DOM) in acid and neutral soils during a 60-day incubation experiment. The proportions of carbon (C) mineralization in Hi-DOM with or without biochar addition were 32.6% or 34.5% in acid soil (P > 0.05) and 15.4% or 22.3% in neutral soil (P < 0.05), respectively. In contrast, those proportions of Ho-DOM-C mineralization with or without biochar addition were 20.0% or 21.4% in acid soil and 19.0% or 20.5% in neutral soil (P > 0.05), respectively. These results showed that biochar could protect Hi-DOM against mineralization in neutral soil but exhibited less effect on Ho-DOM mineralization in both acid and neutral soils. Additionally, biochar did not affect microbial incorporation of Hi- or Ho-DOM in acid and neutral soils. However, biochar notably improved the microbial carbon use efficiency (CUE) of Hi-DOM while it significantly reduced the CUE of Ho-DOM in neutral soil (P < 0.05), indicating that the effect of biochar on microbial CUE was related to organic matter type and soil pH. This study suggests that Hi-DOM can outperform Ho-DOM to decrease C loss and improve microbial CUE in neutral soil with biochar addition. This phenomenon could be due mainly to the different chemical compositions of Hi-DOM and Ho-DOM and their distinct microbial preference. These findings can provide references for biochar's ability to regulate the decomposition of organic matter.

Highly Resolved and Robust Dynamic X-Ray Imaging Using Perovskite Glass-Ceramic Scintillator with Reduced Light Scattering.

All-inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X-ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high-quality and robust X-ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass-ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm-1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X-ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.

Highly Efficient and Thickness Insensitive Inverted Triple-Cation Perovskite Solar Cells Fabricated by Gas Pumping Method.

The gas pumping method (GP) holds the potential of outperforming the antisolvent method (AS) for fabricating perovskite solar cells (PSCs) in many ways such as free of toxic solvents, improved film uniformity, and device reproducibility. Most of the highest power conversion efficiencies (PCEs) of PSCs are still achieved by AS. Successful demonstrations of inverted PSCs produced by GP as well as the corresponding mechanisms are still lacking. Herein, we fabricate highly efficient inverted PSCs by GP delivering an overall efficiency of 21.54%, on par with that of the devices by AS (21.41%), and a superior reproducibility at the optimal film thickness. Nevertheless, as the perovskite film thickness increases, the PCE of GP devices slightly dropped while the AS devices decreased significantly. We found that the AS method tends to produce horizontal grain boundaries due to the heterogeneous solvent extraction while they can be effectively suppresed by the GP method.

Contrasting pathways of carbon sequestration in paddy and upland soils.

Paddy soils make up the largest anthropogenic wetlands on earth, and are characterized by a prominent potential for organic carbon (C) sequestration. By quantifying the plant- and microbial-derived C in soils across four climate zones, we identified that organic C accrual is achieved via contrasting pathways in paddy and upland soils. Paddies are 39%-127% more efficient in soil organic C (SOC) sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates. Upland soils are more replenished by microbial-derived C, whereas paddy soils are enriched with a greater proportion of plant-derived C, because of the retarded microbial decomposition under anaerobic conditions induced by the flooding of paddies. Under both land-use types, the maximal contribution of plant residues to SOC is at intermediate mean annual temperature (15-20°C), neutral soil (pH~7.3), and low clay/sand ratio. By contrast, high temperature (~24°C), low soil pH (~5), and large clay/sand ratio are favorable for strengthening the contribution of microbial necromass. The greater contribution of microbial necromass to SOC in waterlogged paddies in warmer climates is likely due to the fast anabolism from bacteria, whereas fungi are unlikely to be involved as they are aerobic. In the scenario of land-use conversion from paddy to upland, a total of 504 Tg C may be lost as CO2 from paddy soils (0-15 cm) solely in eastern China, with 90% released from the less protected plant-derived C. Hence, preserving paddy systems and other anthropogenic wetlands and increasing their C storage through sustainable management are critical for maintaining global soil C stock and mitigating climate change.

Diazotrophic Community Variation Underlies Differences in Nitrogen Fixation Potential in Paddy Soils Across a Climatic Gradient in China.

Biological nitrogen (N2) fixation as a source of new N input into the soil by free-living diazotrophs is important for achieving sustainable rice agriculture. However, the dominant environmental drivers or factors influencing N2 fixation and the functional significance of the diazotroph community structure in paddy soil across a climatic gradient are not yet well understood. Thus, we characterized the diazotroph community and identified the ecological predictors of N2 fixation potential in four different climate zones (mid-temperate, warm-temperate, subtropical, and tropical paddy soils) in eastern China. Comprehensive nifH gene sequencing, functional activity detection, and correlation analysis with environmental factors were estimated. The potential nitrogenase activity (PNA) was highest in warm-temperate regions, where it was 6.2-, 2.9-, and 2.2-fold greater than in the tropical, subtropical, and mid-temperate regions, respectively; nifH gene abundance was significantly higher in warm-temperate and subtropical zones than in the tropical or mid-temperate zones. Diazotroph diversity was significantly higher in the tropical climate zone and significantly lower in the mid-temperate zone. Non-metric multidimensional scaling and canonical correlation analysis indicated that paddy soil diazotroph populations differed significantly among the four climate zones, mainly owing to differences in climate and soil pH. Structural equation models and automatic linear models revealed that climate and nutrients indirectly affected PNA by affecting soil pH and diazotroph community, respectively, while diazotroph community, C/P, and nifH gene abundance directly affected PNA. And C/P ratio, pH, and the diazotroph community structure were the main predictors of PNA in paddy soils. Collectively, the differences in diazotroph community structure have ecological significance, with important implications for the prediction of soil N2-fixing functions under climate change scenarios.

Low-dose real-time X-ray imaging with nontoxic double perovskite scintillators.

X-rays are widely used in probing inside information nondestructively, enabling broad applications in the medical radiography and electronic industries. X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently. However, the strong self-absorption, relatively low light yield and lead toxicity of these perovskites restrict their practical applications. Here, we report a series of nontoxic double-perovskite scintillators of Cs2Ag0.6Na0.4In1-yBiyCl6. By controlling the content of the heavy atom Bi3+, the X-ray absorption coefficient, radiative emission efficiency, light yield and light decay were manipulated to maximise the scintillator performance. A light yield of up to 39,000 ± 7000 photons/MeV for Cs2Ag0.6Na0.4In0.85Bi0.15Cl6 was obtained, which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr3 (21,000 photons/MeV). The large Stokes shift between the radioluminescence (RL) and absorption spectra benefiting from self-trapped excitons (STEs) led to a negligible self-absorption effect. Given the high light output and fast light decay of this scintillator, static X-ray imaging was attained under an extremely low dose of ∼1 µGyair, and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2 µGyair s-1. After thermal treatment at 85 °C for 50 h followed by X-ray irradiation for 50 h in ambient air, the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged. Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites, not only for avoiding toxicity but also for better performance.

[Responses of Soil Organic Carbon Fractions to Land Use Types in Hilly Red Soil Regions, China].

Land use type exerts important influences on soil organic carbon (SOC) and its fractions, and determines the stability of the carbon pool. Taking woodland as a reference, the content of SOC and its labile fractions[dissolved organic carbon (DOC), microbial biomass carbon (MBC), and particulate organic carbon (POC)] and non-labile fractions[mineral-associated organic carbon (MAOC)] in upland and paddy surface soils in hilly red soil regions were determined to explore the responses of SOC fractions to land use type. The results showed that the contents of SOC, MBC, POC, and MAOC ranked highest in paddy compared with upland and woodland. DOC content in woodland was significantly higher than in upland and paddy (P<0.001). The proportion of each SOC fraction, i.e. DOC/SOC, MBC/SOC, POC/SOC, and MAOC/SOC, was in the range of 0.22%-0.93%, 1.62%-2.70%, 31.08%-40.00%, and 43.22%-56.82%, respectively. The contents of labile fractions (MBC and POC) and their proportions (MBC/SOC and POC/SOC) were in the order of paddy > woodland > upland. MAOC content ranked the highest in paddy but the lowest in upland, while MAOC/SOC exhibited the opposite trend. The correlation suggested that the labile fractions (MBC and POC) and inert fraction (MAOC) were significantly positively correlated with SOC (P<0.001) in the three land use types, while no significant correlations were found between DOC and SOC and its fractions (P>0.05). There was a significant positive correlation between POC and MBC in upland and woodland (P<0.001). POC was significantly positively correlated with MAOC in the three land use types (P<0.001). MAOC and MBC in paddy and upland were significantly positively correlated (P<0.001). Therefore, compared with upland and woodland, SOC in paddy had a higher proportion of labile SOC fraction, but a lower proportion of inert fraction. Moreover, MBC content in paddy was not related to the accumulation of the labile fraction of POC, but positively related to the accumulation of the inert fraction of MAOC. In summary, agricultural land uses have great influence on SOC and its fractions in hilly red soil regions. Though paddy is beneficial for SOC sequestration, the proportions of labile fractions in its SOC are relatively higher, and thus it is vulnerable to loss due to improper agricultural management.

[Characteristics of soil nitrogen cycle and mechanisms underlying the increase in rice yield with partial substitution of mineral fertilizers with organic manure in a paddy ecosystem: A review]. / 稻作系统有机肥替代部分化肥的土壤氮循环特征及增产机制.

Partial substitution of mineral fertilizers with organic manure is a key strategy for stable and increase crop yield accompanying with zero growth of mineral fertilizers. Based on recent stu-dies, we reviewed the effects of partial substitution of mineral fertilizers with organic manure on rice yield, nitrogen utilization efficiency, soil nitrogen fractions, and microbial nitrogen fixation, ammonification, nitrification, and denitrification in rice paddy ecosystems. We further compared the cha-racteristics of soil nitrogen cycle of mineral fertilizers alone and partial substitution of mineral fertili-zers with organic manure. The partial substitution altered key processes of nitrogen cycling, including enhancement of ammonification, mediation of nitrification and denitrification, reduction of ammonia volatilization and nitrogen loss, improved the status of nitrogen supplements (enriching the supplement of low-molecular-weight organic nitrogen, adjusting the distribution of inorganic nitrogen components, increasing the amount of microbial biomass nitrogen, and decreasing the loss of total nitrogen), improved soil nitrogen supply (increasing supply of small molecule organic nitrogen, coordinating inorganic nitrogen components and proportions, and increasing soil microbial biomass nitrogen and total nitrogen fixation), which promoted nitrogen uptake and regulated nitrogen allocation in rice plant to realize stability and enhancement of rice yield.

[Straw Returning Plus Nitrogen Fertilizer Affects the Soil Microbial Community and Organic Carbon Mineralization in Karst Farmland].

The use of straw returning plus nitrogen fertilizer on farmland is one of the important agronomic practices for adjusting soil organic carbon (SOC) transformations. To explore the mechanisms of straw and nitrogen fertilizer application on straw and SOC mineralization in long-term fertilized soils, an incubation experiment with the 13C isotope tracing technique was conducted, which involved three long-term fertilized models in typical karst soils (no fertilization, inorganic fertilization, and a combination of inorganic fertilization and straw). To study the mechanisms of 13C-labeled straw and SOC mineralization, four treatments were designed as follows:no straw and nitrogen (control), and straw combined with three levels of nitrogen fertilizer (0, 214.0, and 571.0 mg·kg-1 soil). The results showed that cumulative mineralization amounts of straw-derived organic carbon in long-term fertilized soils were markedly higher than those in non-fertilized soil. Straw-derived organic carbon mineralization was significantly affected by nitrogen fertilizer levels. The positive priming effects (PE) in long-term fertilized soils were much lower than those in non-fertilized soil. The PE was decreased at the low nitrogen fertilizer level but increased at the high nitrogen fertilizer level. The principal component analysis (PCA) of phospholipid fatty acids (PLFAs) indicated that the soil microbial community structure was greatly affected by the long-term fertilization models and combined straw and nitrogen fertilizer application. Moreover, the content of PLFAs in soil microorganisms, namely, bacteria and fungi, were remarkably increased by the straw plus nitrogen fertilizer (values increased by 40.3%-53.0%, 41.1%-62.6%, and 60.5%-148.6% compared with control), but levels were not significantly affected by nitrogen fertilizer levels alone. The ratios between PLFAs of soil gram-positive and gram-negative bacteria (G+/G-) decreased and were stable at around 0.8. The structure equation models (SEM) demonstrated that the combination of straw and nitrogen affected the soil gram-positive and gram-negative bacteria structure and increased the soil DOC content, which promoted the decomposition of straw and affected the mineralization of SOC. These results indicate that straw returning plus low nitrogen fertilizer can improve the SOC sequestration capacity in karst farmland.