Engineered exosomes in emerging cell-free therapy.

The discovery and use of exosomes ushered in a new era of cell-free therapy. Exosomes are a subgroup of extracellular vesicles that show great potential in disease treatment. Engineered exosomes. with their improved functions have attracted intense interests of their application in translational medicine research. However, the technology of engineering exosomes still faces many challenges which have been the great limitation for their clinical application. This review summarizes the current status of research on engineered exosomes and the difficulties encountered in recent years, with a view to providing new approaches and ideas for future exosome modification and new drug development.

Generation and characterization of PBMCs-derived human induced pluripotent stem cell (iPSC) line SDQLCHi050-A from a healthy donor.

The human induced pluripotent stem cell (iPSC) line SDQLCHi050-A was derived from the PBMCs of a healthy 5-year-old male child. The karyotyping, pluripotency, and trilineage differentiation characteristics were verified in the SDQLCHi050-A line.

Generation and characterization of PBMCs-derived human induced pluripotent stem cell (iPSC) line SDQLCHi051-A from an autism spectrum disorder patient with compound CHD8 gene mutations.

CHD8 mutation is a case of genetic related autism spectrum disorder(ASD), In our research, We describe here the derivation of the iPSC line SDQLCHi051-A from a patient with autism spectrum disorder (ASD) due to two heterozygote mutations (c.6728G > A and c.3876 T > G) in the CHD8 gene. The resulting iPSC line has typical iPSCs characteristics, including pluripotency and trilineage differentiation hallmarks.

Mechanical Characterization and Constitutive Modeling of Nano-Stabilized Soil under Uniaxial Compression.

The stress-strain constitutive model under uniaxial compression is a basic element and important characterization method for determining physical and mechanical properties in cement-based materials research. In this study, a stress-strain constitutive model under uniaxial compression was established, which was based on a new nano-stabilized soil (NSS) through typical mechanical tests and constitutive relationship research. The results indicate that the unconfined compressive strength (UCS) of the nano-stabilized soil was enhanced with the increase in curing period and nano-stabilizer dosage, and that the strength growth rate reaches the maximum at a 12% dosage in the tested samples. The UCS of NSS under a 12% dosage is about 10~15% higher than that of ordinary stabilized soil (SS) without nano doping, and 25~40% higher compared with grade 42.5 cement-soil. The established constitutive model could accurately describe the linear-elastic and elastic-plastic deformation characteristics of NSS under uniaxial compression, which will be conducive to revealing the curve variation law of the stress-strain process. The research results could provide scientific support for the theoretical innovation and engineering application of green environmental protection materials.

Transcription-wide impact by RESCUE-induced off-target single-nucleotide variants in mammalian cells.

RNA base editing is a promising tool in precise molecular therapy. Currently, there are two widely used RNA base editors, REPAIR and RESCUE. REPAIR only facilitates A-to-I conversions, while RESCUE performs both A-to-I and C-to-U conversions. Thus, RESCUE can generate twice the number of mutations compared to REPAIR. However, transcription-wide impact due to RESCUE-induced off-target single-nucleotide variants (SNVs) is not fully appreciated. Therefore, to determine the off-target effects of RESCUE-mediated editing, we employed transcription-wide sequencing on cells edited by RESCUE. The SNVs showed different off-target effects on mRNA, circRNA, lncRNA, and miRNA expression patterns and their interacting networks. Our results illustrate the transcription-wide impact of RESCUE-induced off-target SNVs and highlight the need for careful characterization of the off-target impact by this editing platform.

IKKα kinase silencing increases doxorubicin-induced apoptosis through regulation of oxidative DNA damage response in colon cancer cells.

The inhibitor of kappa B kinase alpha (IKKα) is demonstrated to be involved in the various aspects of cancer biology, from its initiation, to progression, metastasis, and drug resistance. The aim of this study was to investigate the role of IKKα in doxorubicin (DOX)-mediated induction in apoptosis in SW-480 colon cancer cells. Cells were transfected with siRNA against IKKα and treated with DOX. MTT assay was applied to measure SW-480 cell proliferation. The mRNA levels of γ-H2AX within cells were assessed by qRT-PCR. 8-Hydroxy-2'-deoxyguanosine was measured by ELISA. The formation of intracellular reactive oxygen species (ROS) was detected by fluorometry. The antioxidant activities of some enzymes were also determined. For evaluation of apoptosis, ELISA assay was applied. IKKα silencing dramatically increased the doxorubicin cytotoxic effects. In addition, IKKα silencing substantially overexpressed γ-H2AX in SW-480 cells. Furthermore, upon IKKα silencing, the levels of ROS were elevated and the antioxidant defense system was significantly weakened. In addition, IKKα silencing led to the enhancement of apoptotic cells in doxorubicin-treated SW-480 cells. Co-treatment of IKKα and doxorubicin led to the enhanced cellular cytotoxicity via robosting ROS formation, inducing oxidative DNA damage, and decreasing cellular antioxidant defense, and finally potent apoptosis induction in cancer cell lines.

Influence of Biochar on Soil Nutrients and Associated Rhizobacterial Communities of Mountainous Apple Trees in Northern Loess Plateau China.

Biochar application can enhance soil health and alter soil bacterial community structure. However, knowledge relating to biochar on soil nutrients of mountainous apple orchards and then assessing its effect on soil health, especially on soil microorganisms, is still scanty. Therefore, we evaluated the responses of six biochar treatments [Ck (0), T1 (2), T2 (4), T3 (6), T4 (8), and T5 (10) Mg hm-2] with a basal dose of chemical fertilizer on the soil nutrients under potted apple trees across 3, 6, 9, and 12 months, and then investigated the responses of the rhizobacterial communities. Experimental findings demonstrated that: (i) Across the months, the biochar-applied treatment (T5) compared to the control significantly enhanced soil nutrients, including soil pH (2.12 to 2.29%), soil organic matter (35 to 40%), total nitrogen (59 to 65%), ammonium nitrogen (25 to 33%), nitrate nitrogen (163 to 169%), and the activities of urease (76 to 81%), alkaline phosphatase (30 to 33%), catalase (8.89 to 11.70%), and sucrase (23 to 29%). (ii) Compared to the control, the biochar-applied treatment (T5) had a more desirable relative abundance of the bacterial phylum Proteobacteria (35.47%), followed by Actinobacteria (8.59%), Firmicutes (5.74%), and Bacteroidota (2.77%). Similarly, the relative abundance of the bacterial genera in the T5 was Sphingomonas (8.23%) followed by RB41 (3.81%), Ellin6055 (3.42%), Lachnospiracea (1.61%), Bacillus (1.43%), Kineosporia (1.37%), Massilia (0.84%), and Odoribacter (0.34%) than the control. (iii) Among the alpha diversity, the biochar-applied treatment (T5) revealed the highest Chao1 (20%) and ACE (19.23%) indexes, while Shannon (1.63%) and Simpson (1.02%) had relatively lower indexes than the control. Furthermore, positive correlations were found between the soil nutrients and some of the abundant bacterial phyla. Overall, the findings of this research demonstrated that biochar application at 10 Mg hm-2 (T5) along with the required chemical fertilizer is beneficial to improve soil health and pave the way for sustainable production in apple orchards of the northern loess plateau.

Developing PspCas13b-based enhanced RESCUE system, eRESCUE, with efficient RNA base editing.

RNA base editing is potential for cellular function research and genetic diseases treating. There are two main RNA base editors, REPAIR and RESCUE, for in vitro use. REPAIR was developed by fusing inactivated Cas13 (dCas13) with the adenine deaminase domain of ADAR2, which efficiently performs adenosine-to-inosine (A-to-I) RNA editing. RESCUE, which performs both cytidine-to-uridine (C-to-U) and A-to-I RNA editing, was developed by fusing inactivated Cas13 (dCas13) with the evolved ADAR2. However, the relatively low editing efficiency of the RESCUE system limits its broad application. Here, we constructed an enhanced RESCUE (eRESCUE) system; this dPspCas13b-RESCUE-NES system was generated by fusing inactivated PspCas13b with the evolved ADAR2. We determined the endogenous mRNA A-to-I and C-to-U editing efficiency mediated by the dPspCas13b-RESCUE-NES system in HEK-293T cells. This new RNA base editor was then used to induce 177Ser/Gly conversion of inhibitor kappa B kinase ß (IKKß) by changing the genetic code from AGU to GGU. The results showed that the eRESCUE editor mediates more efficient A-to-I and C-to-U RNA editing than the RESCUE RNA editor, as was previously reported. The 177Ser/Gly conversion of IKKß, accomplished by converting the genetic code from AGU to GGU, resulted in a decrease in the phosphorylation of IKKß and downregulation of downstream IKKß-related genes. In summary, we developed a more efficient RNA base editor, eRESCUE, which may provide a useful tool for biomedical research and genetic disease treatment. Video Abstract.

ecRESCUE: a novel ecDHFR-regulated RESCUE system with reduced RNA off-targeting activity.

The currently available RESCUE RNA base editing system demonstrates considerable potential for the treatment of genetic diseases at the transcriptional level. However, the relatively high incidence of off-target events hampers the precise RNA editing, thereby limiting its use in the clinical setting. This study describes a new RNA base editing method, named ecRESCUE, which utilizes inducible stabilization of the protein ecDHFR DD fused at the C-terminal of the original RESCUE system. In vitro experiments in 293T cells showed that the ecRESCUE editor markedly reduced the incidence of off-target single nucleotide polymorphisms without affecting the RNA A-to-I and C-to-U base editing efficiency. Altogether, these results demonstrate that the inducible ecRESCUE system represents an attractive approach to regulate and improve the outcome of the available RNA base editor with reduced off-targeting activity. Video Abstract.

Genome-Wide Association Identifies Risk Pathways for SAPHO Syndrome.

SAPHO syndrome is a rare chronic inflammatory disease which is characterized by the comprehensive manifestations of bone, joint, and skin. However, little is known about the pathogenesis of SAPHO syndrome. A genome-wide association study (GWAS) of 49 patients and 121 control subjects have primarily focused on identification of common genetic variants associated with SAPHO, the data were analyzed by classical multiple logistic regression. Later, GWAS findings were further validated using whole exome sequencing (WES) in 16 patients and 15 controls to identify potentially functional pathways involved in SAPHO pathogenesis. In general, 40588 SNPs in genomic regions were associated with P < 0.05 after filter process, only 9 SNPs meet the expected cut-off P-value, however, none of them had association with SAPHO syndrome based on published literatures. And then, 15 pathways were found involved in SAPHO pathogenesis, of them, 6 pathways including osteoclast differentiation, bacterial invasion of epithelial cells, et al., had strong association with skin, osteoarticular manifestations of SAPHO or inflammatory reaction based published research. This study identified aberrant osteoclast differentiation and other pathways were involved in SAPHO syndrome. This finding may give insight into the understanding of pathogenic genes of SAPHO and provide the basis for SAPHO research and treatment.

A Study of Rainfall-Runoff Movement Process on High and Steep Slopes Affected by Double Turbulence Sources.

To increase the available land area, a large-scale land remediation campaign was carried out in the loess hilly and gully area. A large number of high and steep slopes have been produced in the construction of road engineering and water conservancy engineering, and these slopes will cause serious soil erosion under rainfall conditions. Because rainfall runoff is simultaneously affected by slope, bed surface and rainfall, the runoff movement characteristics are complex. It is difficult to consider all influencing factors in the existing models, especially for steep slopes. In this study, artificial rainfall experiments were conducted to study the rainfall-runoff hydraulic processes under different rainfall intensities and slope gradients, and a modified method was proposed to model the key hydraulic parameters (i.e., equilibrium time, water surface line, and runoff processes) on steep slopes. The results showed that (1) For steep slopes (a 70° slope compared to a 5° slope), the runoff generation time, confluence time and equilibrium time of the slope decreased significantly. At the same time, the single width runoff of the steep slope had a power function relationship with the rainfall intensity and gradient. (2) The runoff patterns of steep slopes were different from those on gentle slopes and runoff patterns were more likely to change. The Reynolds number and Froude number for slope flow changed slowly when the slope was less than the critical gradient and increased significantly when the slope exceeded the critical gradient. (3) Based on the analysis of the "double turbulent model theory of thin-layer flow on a high-steep slope", combined with the dispersed motion wave model, a modified method for calculating the hydrodynamic factors of rainfall runoff was proposed. Then, this method was verified with indoor and outdoor experiments. The research results not only have theoretical significance, but also provide a more accurate calculation method for the design of high and steep slopes involved in land treatment engineering, road engineering and water conservancy engineering.

Amelioration of muscular spasm-induced pain of Guangtongxiao recipe in a non-everted gut sac in vitro model.

BACKGROUND: The modern study of the traditional Chinese medicine (TCM) compound recipes is a complex issue because of the large number of components in the recipes that would produce several metabolites after entering the body. The TCM compound recipes are known to have the advantage of synergistic treatment by multiple targets due to diverse components. Therefore, a research method that can reflect the overall effect of compounds with multi-components is essential. The pharmacological studies of the classic TCM compound recipes mainly use the sero-pharmacological method. It is a semi-in vivo study method, and the drug to be tested in the in vitro experiment is the drug-containing serum from the model animals (the drug to be tested is a mixed drug system containing the prototype drugs in animal bodies that have pharmacodynamic effects and the metabolites). Herein, a safe and effective external TCM recipe was used to develop another semi-in vivo experimental method to reflect the overall effects of TCM. AIM: To observe the effects of in-vitro intestinal absorption liquid of aqueous extracts of the TCM compound recipe-Guangtongxiao foam aerosol (Guangtongxiao)-on the tension of isolated rectal rings of mouse and investigate the underlying mechanisms of antispasmodic and amelioration of muscular spasm-induced pain. METHODS: Intestinal absorption liquid of the Guangtongxiao aqueous extract at the five time points (30, 45, 75, 105, and 120 min) was prepared using a non-everted gut sac method. The isolated rectal rings of mice were prepared by pre-contraction using potassium chloride (KCl) or acetylcholine chloride (ACh) to make steady contraction. The intestinal absorption liquid were added cumulatively to the sink with the constricted rectal rings. The effects of the five groups of the intestinal absorption liquid with different drug concentration were observed on the tension of the isolated rectal rings. Then the ex vivo perfusion of the mouse rectal ring was performed as same as Guangtongxiao intestinal absorption liquid experiments, and the effects of two major components of Guangtongxiao, paeoniflorin (Pae) and tetrahydropalmatine (THP), on the rectal ring pre-treated with high concentration of KCl and ACh to induce contraction were studied. RESULTS: The relaxation rate of the five groups of the intestinal canals increased significantly with 3200 µL cumulative sample volume as compared to the blank group (P < 0.01). It suggested that the relaxation activity of the intestinal absorption liquid enhanced significantly with the prolongation of the interaction between isolated rectal rings and intestinal absorption liquid in a time-dependent manner. Also, significant differences were detected while comparing between the 120-min intestinal absorption liquid group and the blank group with respect to various cumulative sampling volumes (P < 0.01). In addition, the intestinal relaxation rate elevated gradually with the increase in sampling volume, indicating that the concentrations of active substances in the intestinal absorption liquid prepared by the non-everted gut sac model increased and the intestinal relaxation activity was enhanced with the prolongation of the absorption time in a dose-dependent manner. And Pae and THP in a concentration-dependent manner caused relaxation of the rectal ring, which is pretreated with high K+(KCl) and ACh to induce contraction. The EC50 of Pae and THP was 8.67 × 10-5 M (6.68 × 10-5-1.13 × 10-4) and 1.41 × 10-4 M (1.24 × 10-4-1.61 × 10-4) in the contraction model induced by KCl, and was 6.15 × 10-5 M (4.47 × 10-5-8.45 × 10-5), and 1.31 × 10-4 M(1.22 × 10-4-1.42 × 10-4) in the model induced by ACh, respectively. CONCLUSION: The intestinal absorption liquid of Guangtongxiao exerted a remarkable relaxation activity for the rectal rings, and relaxation of the smooth muscle tension might be one of the antispasmodic mechanisms of Guangtongxiao compound recipe. Also, adopting a semi-in-vivo experimental method to study the efficacy of topical external TCM recipe medicine is optimal.

Profiling of the pattern of the human TRB/IGH-CDR3 repertoire in primary biliary cholangitis patients.

INTRODUCTION: Primary biliary cholangitis (PBC) is characterized by lymphocyte cell-induced immune destruction of cholangiole. However, the immunological characteristics of peripheral blood cells in PBC patients remain unknown. This study was designed to reveal the differences in the immunological characteristics between PBC patients and healthy adults. METHODS: We performed high-throughput sequencing to determine the TRB-CDR3 and IGH-CDR3 repertoires of T and B cells in 19 healthy controls and 29 PBC patients. Different immunological characteristics, such as distinctive complementarity determining region 3 (TRB-CDR3) lengths, usage bias of V and J segments, and random nucleotide addition were identified in PBC and healthy control (HC) groups. RESULTS: The diversity of TRB-CDR3 was significantly lower in the PBC group compared with the HC group. CDR3 and the N addition length distribution were significantly changed compared with the HC group. It appeared that the PBC group had more short N additions and the HC group had more long N additions in the TRB-CDR3 repertoire. The results also revealed a set of PBC-associated clonotypes compared with the HC group. CONCLUSION: This study suggested that PBC is a complex autoimmune disease process with evidence of different TRB-CDR3 rearrangements compared with healthy adults that share IGH-CDR3 peptides with some autoimmune diseases. This new insight may contribute to a better understanding of the immune functions of PBC patients and benefit efficient applications of PBC diagnosis and treatments.

Study on the Mechanism of Nano-SiO2 for Improving the Properties of Cement-Based Soil Stabilizer.

A new nano-soil stabilizer (N-MBER, Nanometer Material Becoming Earth into Rock) material was developed in this research by using the high activity and ultrafine properties of nano-SiO2 (NS), which were able to improve the properties of cement-based soil stabilizer and had broad application prospects. The results showed that (1) the strength of N-MBER obeyed a compound function relation with curing period and additive amount of NS. The relationship between strength and curing period obeyed an exponential function when the additive amount was constant. The strength and additive amount were a power function when the curing period was fixed. The compressive strength of N-MBER increased by more than 15% compared with MBER at day 28 of the curing period, and 50% compared with grade 32.5 cement. (2) The pozzolanic catalytic activity of NS significantly increased the amount of calcium silicate hydrate gel (C-S-H) in the N-MBER colloid. NS was also able to make the distribution of the network structure of colloidal space more uniform and improved the fractal dimension of particles by 0.05. The above results provide theoretical data for exploring the mechanism of soil stabilizer strength growth and for promoting the application of solid waste utilization.

Copy Number Variation of Multiple Genes in SAPHO Syndrome.

OBJECTIVE: SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) syndrome is a type of rare chronic aseptic inflammation of unknown etiology. To date, no research to our knowledge has reported copy number variation (CNV) of genes that could affect predisposition to SAPHO syndrome. We investigated the association between CNV profile and SAPHO syndrome. METHODS: We used array comparative genomic hybridization (CGH) to screen for CNV in a nuclear family including 2 patients and a healthy control. We then validated the copy numbers of candidate genes found in the array CGH assay and other candidate genes by TaqMan real-time PCR in 360 case and control samples. RESULTS: Ten regions from 8 chromosomes were found to have abnormal gene copies in the nuclear family, so the CNV of candidate genes (ADAM5, CSF2RA, IL3RA, and 9 other genes) were tested by TaqMan PCR. Significant copy number loss of CSF2RA (p = 0.000) and NOD2 (p = 0.005), and significant copy number gain of MEGF6 (p = 0.002) and ADAM5 (p = 0.000) were seen in patients with SAPHO compared with controls at the a = 0.05 level. There were no differences in the other 8 candidate genes between patient and control samples (p > 0.05). CONCLUSION: Our study established the first association between CNV in CSF2RA, NOD2, MEGF6, and ADAM5 and SAPHO syndrome. These findings may offer insight into the pathogenesis of SAPHO and provide the basis for improved diagnosis and treatment.

Shifts of sediment transport regime caused by ecological restoration in the Middle Yellow River Basin.

Sediment in rivers is the dominant material source for ecosystems in lower reaches and estuaries, and it is undergoing large variations globally in recent decades. Though we have knowledge that human activities are greatly affecting land surface ecosystem processes and functions, the relationships between sediment transport regime and the intensifying human activities, are still poorly understood. This study was to investigate the changes of sediment transport regime due to the large-scale ecological restoration in the Middle Yellow River Basin (MYRB). In this study, we examined the change of the sediment rating curves using daily sediment load and streamflow data from 30 stations during time periods including pre- and post-ecological restoration in this region. We found the pair-relationship of the rating parameters (coefficient and exponent), denoted as coefficient-exponent pair-line, is a critical indicator that can detect the shift of sediment transport regime due to disturbed land surface conditions, though the changed hydrometeorological condition may just influence the absolute values of the rating parameters. Our analysis indicates there was a significant and interesting change of the sediment transport regime in the MYRB characterized by the consistent shift of the coefficient-exponent pair-line, together with an increasing exponent and a decreasing coefficient. This changed sediment transport regime can tell that sediment delivery would become lower for normal discharge conditions but potentially higher for extreme discharge conditions, and this phenomenon seems more distinct in relatively smaller watersheds, suggesting a higher risk of the potential high sediment delivery for extreme rainfall conditions especially for small watersheds. Our study would be informative and valuable to decision makers for sustainable watershed management in the MYRB when considering the changed sediment delivery.

Association analysis of interleukin-23 receptor SNPs and SAPHO syndrome in Chinese people.

OBJECTIVE: SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, and osteitis) is an autoimmune disease of unknown etiology that seriously affects patients' daily lives. Family-based investigations support genetic contributions toward disease susceptibility. The present study evaluated whether the previously reported autoimmune disease-associated single nucleotide polymorphisms (SNPs) have any genetic overlap with SAPHO syndrome. METHOD: Genomic DNA was obtained from 71 SAPHO patients and 104 healthy controls. The SNP genotypes of each patient were determined with polymerase chain reaction and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Genotype, allele, and haplotype frequencies were analyzed with SPSS software. RESULTS: Three SNP sites (rs10889677 and rs2201841 of interleukin [IL]-23R, and rs2243248 of IL-4) showed significant correlation with the occurrence of SAPHO syndrome in additive and dominant genetic models, while rs7517847 of IL-23R showed substantial correlation with SAPHO in the dominant genetic model. The G allele of rs2243248 (IL-4) was a high risk factor for SAPHO (P = 2.41e-5, odds ratio [OR] =7.79, 95% CI: 2.59-23.3). The haplotype (A-G-C-G-T), comprising 5 SNPs of the IL-23R gene, had a significantly higher frequency in the SAPHO cohort than in the controls (P = .011, OR = 2.05, 95% CI: 1.12-3.60). CONCLUSION: Variants rs10889677, rs2201841, and rs7517847 of IL-23R, and variant rs2243248 of IL-4, showed strong associations with SAPHO syndrome. Patients carrying the A-G-C-G-T haplotype of IL-23 are significantly more likely to develop SAPHO syndrome.

Nitrate Accumulation and Leaching in Surface and Ground Water Based on Simulated Rainfall Experiments.

To evaluate the process of nitrate accumulation and leaching in surface and ground water, we conducted simulated rainfall experiments. The experiments were performed in areas of 5.3 m2 with bare slopes of 3° that were treated with two nitrogen fertilizer inputs, high (22.5 g/m2 NH4NO3) and control (no fertilizer), and subjected to 2 hours of rainfall, with. From the 1st to the 7th experiments, the same content of fertilizer mixed with soil was uniformly applied to the soil surface at 10 minutes before rainfall, and no fertilizer was applied for the 8th through 12th experiments. Initially, the time-series nitrate concentration in the surface flow quickly increased, and then it rapidly decreased and gradually stabilized at a low level during the fertilizer experiments. The nitrogen loss in the surface flow primarily occurred during the first 18.6 minutes of rainfall. For the continuous fertilizer experiments, the mean nitrate concentrations in the groundwater flow remained at less than 10 mg/L before the 5th experiment, and after the 7th experiment, these nitrate concentrations were greater than 10 mg/L throughout the process. The time-series process of the changing concentration in the groundwater flow exhibited the same parabolic trend for each fertilizer experiment. However, the time at which the nitrate concentration began to change lagged behind the start time of groundwater flow by approximately 0.94 hours on average. The experiments were also performed with no fertilizer. In these experiments, the mean nitrate concentration of groundwater initially increased continuously, and then, the process exhibited the same parabolic trend as the results of the fertilization experiments. The nitrate concentration decreased in the subsequent experiments. Eight days after the 12 rainfall experiments, 50.53% of the total nitrate applied remained in the experimental soil. Nitrate residues mainly existed at the surface and in the bottom soil layers, which represents a potentially more dangerous pollution scenario for surface and ground water. The surface and subsurface flow would enter into and contaminate water bodies, thus threatening the water environment.

Application of modified export coefficient method on the load estimation of non-point source nitrogen and phosphorus pollution of soil and water loss in semiarid regions.

Chinese Loess Plateau is considered as one of the most serious soil loss regions in the world, its annual sediment output accounts for 90 % of the total sediment loads of the Yellow River, and most of the Loess Plateau has a very typical characteristic of "soil and water flow together", and water flow in this area performs with a high sand content. Serious soil loss results in nitrogen and phosphorus loss of soil. Special processes of water and soil in the Loess Plateau lead to the loss mechanisms of water, sediment, nitrogen, and phosphorus are different from each other, which are greatly different from other areas of China. In this study, the modified export coefficient method considering the rainfall erosivity factor was proposed to simulate and evaluate non-point source (NPS) nitrogen and phosphorus loss load caused by soil and water loss in the Yanhe River basin of the hilly and gully area, Loess Plateau. The results indicate that (1) compared with the traditional export coefficient method, annual differences of NPS total nitrogen (TN) and total phosphorus (TP) load after considering the rainfall erosivity factor are obvious; it is more in line with the general law of NPS pollution formation in a watershed, and it can reflect the annual variability of NPS pollution more accurately. (2) Under the traditional and modified conditions, annual changes of NPS TN and TP load in four counties (districts) took on the similar trends from 1999 to 2008; the load emission intensity not only is closely related to rainfall intensity but also to the regional distribution of land use and other pollution sources. (3) The output structure, source composition, and contribution rate of NPS pollution load under the modified method are basically the same with the traditional method. The average output structure of TN from land use and rural life is about 66.5 and 17.1 %, the TP is about 53.8 and 32.7 %; the maximum source composition of TN (59 %) is farmland; the maximum source composition of TP (38.1 %) is rural life; the maximum contribution rates of TN and TP in Baota district are 36.26 and 39.26 %, respectively. Results may provide data support for NPS pollution prevention and control in the loess hilly and gully region and also provide scientific reference for the protection of ecological environment of the Loess Plateau in northern Shaanxi.