Deep Nitrate Accumulation in a Highly Weathered Subtropical Critical Zone Depends on the Regolith Structure and Planting Year.

Nitrate accumulated deep (>100 cm) in the regolith (soil and saprolite) threatens groundwater quality, but most studies focus only on nitrate nearer the surface (<100 cm). Surface soil management versus regolith interactions affect deep nitrate leaching, but their combined impact remains unclear. This study measured how deep nitrate accumulation was affected by crop practices including orchard/cropland planting years, regolith structure, and soil properties in highly weathered subtropical red soils. Deep nitrate storage varied from 43.6 to 1116.3 kg ha-1. Regolith thickness was positively correlated with nitrate storage (R2 = 0.43, p < 0.05). Reticulated red clay (110-838 cm) had 81% of the accumulated nitrate and overlapped with 79% of the nitrate accumulation layer. All of the nitrate accumulation parameters (except for peak depth (PD)) generally increased with the planting years. The difference in peak nitrate concentration (9.0-20.0 mg kg-1) with planting year gradient (3-58 years) varied by 2.2 times, and the difference in nitrate storage (43.6-425.7 kg ha-1) varied by 9.8 times. Texture and pH explain 41.6% of the variation in nitrate concentration. As soil management practices interact with deeper regolith to control the spatial pattern of nitrate accumulation, vulnerable regions could be identified to avoid high accumulation.

Gubenyiliu II Inhibits Breast Tumor Growth and Metastasis Associated with Decreased Heparanase Expression and Phosphorylation of ERK and AKT Pathways.

Gubenyiliu II (GYII), a Traditional Chinese Medicine (TCM) formula used in our hospital, has shown beneficial effects in cancer patients. In this study, we investigated the molecular mechanisms underlying the beneficial effects of GYII on murine breast cancer models. GYII showed significant inhibitory effects on tumor growth and metastasis in the murine breast cancer model. Additionally, GYII suppressed the proliferation of 4T1 and MCF-7 cells in a dose-dependent manner. A better inhibitory effect on 4T1 cell proliferation and migration was found in the decomposed recipes (DR) of GYII. Moreover, heparanase expression and the degree of angiogenesis were reduced in tumor tissues. Western blot analysis showed decreased expression of heparanase and growth factors in the cells treated with GYII and its decomposed recipes (DR2 and DR3), and thereby a reduction in the phosphorylation of extracellular signal-regulated kinase (ERK) and serine-threonine kinase (AKT). These results suggest that GYII exerts anti-tumor growth and anti-metastatic effects in the murine breast cancer model. The anti-tumor activity of GYII and its decomposed recipes is, at least partly, associated with decreased heparanase and growth factor expression, which subsequently suppressed the activation of the ERK and AKT pathways.

Characterization of the spatial variability of soil available zinc at various sampling densities using grouped soil type information.

The influence of anthropogenic activities and natural processes involved high uncertainties to the spatial variation modeling of soil available zinc (AZn) in plain river network regions. Four datasets with different sampling densities were split over the Qiaocheng district of Bozhou City, China. The difference of AZn concentrations regarding soil types was analyzed by the principal component analysis (PCA). Since the stationarity was not indicated and effective ranges of four datasets were larger than the sampling extent (about 400 m), two investigation tools, namely F3 test and stationarity index (SI), were employed to test the local non-stationarity. Geographically weighted regression (GWR) technique was performed to describe the spatial heterogeneity of AZn concentrations under the non-stationarity assumption. GWR based on grouped soil type information (GWRG for short) was proposed so as to benefit the local modeling of soil AZn within each soil-landscape unit. For reference, the multiple linear regression (MLR) model, a global regression technique, was also employed and incorporated the same predictors as in the GWR models. Validation results based on 100 times realization demonstrated that GWRG outperformed MLR and can produce similar or better accuracy than the GWR approach. Nevertheless, GWRG can generate better soil maps than GWR for limit soil data. Two-sample t test of produced soil maps also confirmed significantly different means. Variogram analysis of the model residuals exhibited weak spatial correlation, rejecting the use of hybrid kriging techniques. As a heuristically statistical method, the GWRG was beneficial in this study and potentially for other soil properties.

Reconstruction of Digital Skin Defects with the Free Wrist Crease Flap.

BACKGROUND: Soft-tissue digital defects frequently need to be covered by a flap rather than a skin graft. In hand surgery, functional preservation and aesthetic appearance are often as important as procedural efficacy. OBJECTIVE: We present our clinical experience with reconstruction of digital skin defects with the free wrist crease flap. METHODS: From January 2012 to September 2013, 14 digits of 14 patients (10 males, 4 females) were included for evaluation. The procedure was performed with brachial plexus block anesthesia. The superficial palmar branch of the radial artery, a subcutaneous superficial vein, and the palmar cutaneous branch of the median nerve were included in the free wrist crease flap. The flaps were used to reconstruct the skin defect of injured digits through microvascular anastomosis, and donor sites were closed primarily. RESULTS: Postoperative follow-up time ranged from 3 to 25 months. All digital deformities were corrected, all flaps survived completely without ischemia, and none were aesthetically bulky. The area of free wrist crease flaps ranged from 2.5 to 5.0 cm by 2.0 to 3.1 cm. Slight wound infections appeared in two cases. Venous crisis occurred in one case, but it was successfully addressed after vascular exploration and reanastomosis. Sensation determined by static two-point discrimination measured in these flaps 2 months postsurgery was "good" at a mean 9.7 ± 2.1 mm (range, 6-14 mm). The mean motion range of the distal interphalangeal joint and proximal interphalangeal joint was 23.4 ± 6.9 degrees (0-42 degrees) and 75.8 ± 22.1 degrees (0-98 degrees) preoperatively. The mean motion range of the distal interphalangeal joint recovered to 40.3 ± 5.7 degrees (36-42 degrees), and that of the proximal interphalangeal joint was 90.3 ± 15.3 degrees (85-98 degrees) postoperatively. Both joints reached normal motion angle and difference was statistically significant preoperatively and postoperatively (p < 0.05). The mean disabilities of arm and shoulder (DASH) score was 6.8 ± 3.4 (0-15), and there was statistically significant difference when compared with the preoperative score of 13.5 ± 4.3 (3-19) (p < 0.05). CONCLUSION: We found the free wrist crease flap to be an ideal solution for reconstruction of skin defects of digits.

T-shaped excision of the orbicularis oris muscle: an innovative technique for upper lip lift procedures.

BACKGROUND: The lips are a prominent part of the face and they age along with the face. Microsurgery for upper lip lifts is becoming popular because of its association with minimal trauma and rapid recovery. OBJECTIVES: The authors introduced an innovative method of lifting the upper lip. METHODS: From January 2009 to March 2013, a cohort of 30 women underwent an upper lip lift surgical procedure. Patients received local anesthesia for a regional block of the infraorbital nerve. A T-shaped orbicularis oris and a strip of skin were excised. The superior edge of the orbicularis oris muscle was sutured to the base of the nose, and the incision was closed with a continuous intradermal suture. Postoperative follow-up time ranged from 1 to 5 years. RESULTS: At the time of follow-up, the incisional scar was not visible on the patient. The nasolabial angle was 96.20° ± 1.86° before operation and 88.23° ± 2.58° after operation. The difference was statistically significant (P = 0.000 and P < 0.001). The upper lip angle was 65.56° ± 8.60° before operation and 51.90° ± 3.93° after operation. The difference was statistically significant (P = 0.000) and P < 0.001). After operation, the upper lip appeared to be clearly thickened. CONCLUSIONS: This innovative surgical technique is a simple and effective way to lift the upper lip.

[Study on Paddy Soil Chronosequences Based on Visiblc-Near Infrared Diffuse Reflectance Spectra].

To investigate spectral characteristics of different soil compositions, eight soil profiles from two paddy soil chronosequences developed on red clays and red sandstones respectively were collected in Jiangxi Province. A total of 37 soil samples were taken from each soil horizons of the profiles. The paddy soil chronosequences were chosen mainly because all soil profiles have the same land management and thus parent materials and rice cultivation time would be two major soil formative factors. This makes it possible to study spectral response characteristics of soil organic matter (SOM) and parent material characteristics. We measured diffuse reflectance spectra data of soil samples using the Cary 5000 spectrophotometer at 350-2500 nm spectral range. Spectral response characteristics of SOM and inorganic minerals in paddy soils were analyzed according to different soil horizons, soil forming times and parent materials. Experiment results showed that for soil samples from a single parent material, overall reflectance presented by PC_1 score can be calibrated for soil organic matter (SOM) content with high precision (R(RC)² = 0.91, R(RS)² = 0.79), even though the SOM content was low (not more than 20 g · kg⁻¹). The absorption strength (AS) at 1400, 1900 and 2200 nm was mainly affected by the minerals inherited from parent materials. And the more the sample was near to bottom of a soil profile, the higher the AS value. Samples with the same mineral components had the similar AS ratio among these three wavelength locations. The differences in parent materials can significantly affect spectral curve shape and spectral absorption strength. To make the calibration more interpretative, parent material factors should be considered.

Nitrogen loss through anaerobic ammonium oxidation coupled to iron reduction from paddy soils in a chronosequence.

Anaerobic ammonium oxidation coupled to iron(III) reduction (termed Feammox) with dinitrogen, nitrite, or nitrate as the end-product is a recently discovered process of nitrogen cycling. However, Feammox has not been described in paddy soils, which are rich in iron(III) oxides and subjected to intensive nitrogen fertilization. Here, evidence for Feammox in a paddy soil chronosequence with a gradient of microbially reducible iron(III) levels was obtained in Southern China using (15)N-labeled ammonium-based isotopic tracing and acetylene inhibition techniques. Our study demonstrated the occurrence of Feammox in the chronosequence, and direct dinitrogen production was shown to be the dominant Feammox pathway. Within the chronosequence, three paddy soils with higher microbially reducible iron(III) levels had higher Feammox rates (ranged from 0.17 to 0.59 mg N kg(-1) d(-1)) compared to an uncultivated soil (0.04 mg N kg(-1) d(-1)). It is estimated that a loss of 7.8-61 kg N ha(-1) year(-1) is associated with Feammox in the examined paddy soils. Overall, we discover that rice cultivation could enrich microbially reducible iron(III), accelerate Feammox reaction and thus fuel nitrogen loss from soils, and suggest that Feammox could be a potentially important pathway for nitrogen loss in paddy soils.

Edaphic regulation of soil organic carbon fractions in the mattic layer across the Qinghai-Tibetan Plateau.

The mattic layer is a main ecological function bearer of alpine meadow soils in the Qinghai-Tibet Plateau. It has high soil organic carbon (SOC) content with a variety of SOC fractions, which are thought to have different sensitivities to climate change. The effects of soil properties and climate on the SOC fractions in the mattic layer are not well understood. To address this, we analyzed the effects of environmental factors on two SOC fractions: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). A random forest model (RFM), partial correlation analysis, and structural equation model (SEM) were used to quantify the relative effects of soil and climatic factors on SOC fractions. We found that SOC and its fractions are primarily regulated by soil properties rather than climate. Partial correlation analysis and SEM revealed that climate indirectly affects SOC by influencing soil properties. Silt+Clay and exchangeable calcium (Caex) were found to be the strongest contributing factors of MAOC and POC, respectively. A distinct shift occurs in the mechanism underlying SOC stabilization with varying soil pH. In acidic and neutral environments, amorphous Al/Fe-(hydr) oxides contribute to the stability of MAOC, whereas free Al/Fe-(hydr) oxides promote SOC mineralization. Conversely, Caex positively influences the stabilization of both POC and MAOC throughout the pH range. These results can be extrapolated to predict SOC dynamics in future soil conditions affected by environmental change, especially for use in Earth system models.

Synergy of de-walled Ganoderma Lucidum spore powder (GLSP) on targeted therapy in advanced non-squamous non-small cell lung cancer with epidermal growth factor receptor (EGFR) mutant: protocol for a randomized, double-blind, placebo-controlled study.

BACKGROUND: Osimertinib is regarded as a promising third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) for advanced non-squamous non-small cell lung cancer (NSCLC) patients who developed T790M. However the adverse effects, primarily fatigue, remain an overwhelming deficiency of Osimertinib, hindering it from achieving adequate clinical efficacy for such NSCLC. Ganoderma lucidum has been used for thousands of years in China to combat fatigue, while Ganoderma Lucidum spores powder (GLSP) is the main active ingredient. The aim of this study is to investigate whether GLSP is sufficiently effective and safe in improving fatigue and synergizing with Osimertinib in non-squamous NSCLC patients with EGFR mutant. METHOD/DESIGN: A total of 140 participants will be randomly assigned to receive either de-walled GSLP or placebo for a duration of 56 days. The primary outcome measure is the fatigue score associated with EGFR-TKI adverse reactions at week 8, evaluated by the Chinese version of the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire for Cancer Patients (QLQ-C30). Secondary outcomes include evaluation of treatment effectiveness, assessment of quality of life (QoL), and exploration of immune indicators and gut microbiota relationships. Following enrollment, visits are scheduled biweekly until week 12. TRIAL REGISTRATION: China Clinical Trial Registry ChiCTR2300072786. Registrated on June 25, 2023.

Nitrate leaching characteristics of red soils from different parent materials in subtropical China.

Globally, nitrate (NO3-) leaching from agroecosystems has been of major concern. There is evidence that NO3- leaching exhibits intense seasonal variation in subtropical regions. However, influencing factors to the seasonal dynamics remain unclear. In this study, a two-year field lysimeters experiment was conducted with three red soils derived from different parent materials (Quaternary red clay (QR), red sandstone (RS), and basalt (BA)). An N fertilizer (15N-enriched urea, 10 atom% excess) of 200 kg N ha-1 yr-1 was applied for maize. The effect of parent material on NO3- leaching characteristics was examined in surface (0-20 cm) and subsoil (20-100 cm) layers. The results showed due to the weakening of abundant drainage, there was no significant effect of parent materials on NO3- leaching characteristics in surface layers. Environmental factors (precipitation and temperature) and fertilization together led to obvious seasonal characteristics, i.e. abundant NO3- leaching during both crop growth and fallow periods. In subsoil layers, NO3- leaching characteristics were completely different among three soils. The concentrations and δ15N of NO3- in QR and RS soils showed a continuous increase after first year's fertilization, while those in BA soil remained relatively stable after reaching peak levels around harvest in first year. Meanwhile, the NO3- leaching amount in BA soil was significantly lower than in the other two soils. These might be explained by different NO3- adsorption capacities caused by the differences in mineral composition and free iron and aluminium contents. These elucidated in subsoil layers, NO3- leaching characteristics highly depended on parent materials. Meanwhile, adsorption capacity was limited and cannot slow NO3- leaching in the long run. Our results suggest that seasonal variation of NO3- leaching in surface layers and temporary retardant effect from NO3- adsorption capacity in subsoil layers should receive much attention when calculating and predicting NO3- leaching in subtropical regions.

Size, distribution, and vulnerability of the global soil inorganic carbon.

Global estimates of the size, distribution, and vulnerability of soil inorganic carbon (SIC) remain largely unquantified. By compiling 223,593 field-based measurements and developing machine-learning models, we report that global soils store 2305 ± 636 (±1 SD) billion tonnes of carbon as SIC over the top 2-meter depth. Under future scenarios, soil acidification associated with nitrogen additions to terrestrial ecosystems will reduce global SIC (0.3 meters) up to 23 billion tonnes of carbon over the next 30 years, with India and China being the most affected. Our synthesis of present-day land-water carbon inventories and inland-water carbonate chemistry reveals that at least 1.13 ± 0.33 billion tonnes of inorganic carbon is lost to inland-waters through soils annually, resulting in large but overlooked impacts on atmospheric and hydrospheric carbon dynamics.

A comparison of skin expansion and contraction between one expander and two expanders: a preliminary study.

BACKGROUND: This study aimed to compare the difference between the skin expansion and contraction rates for an expanded flap with one versus two expanders. METHODS: The study cohort comprised 24 cases of two overlapping expanders and 15 cases of a single implanted expander involving 22 patients. The method of "wet-cloth sampling" was applied to measure the expanded flap area and the initial unexpanded area and to calculate the skin expansion rate. Two points 5 cm apart in the center of the expanded flap were selected before the second surgical stage. After removal of the expander, the distance between the two fixed points was measured and recorded. The contraction rate of the expanded flap then was calculated. RESULTS: During the same period of expansion in the two groups (p = 0.06, >0.01), the skin expansion rate was 3.5 ± 0.9 % in the group with two overlapping expanders and 2.6 ± 0.6 % in the control group. The difference between the two groups was statistically significant (p = 0.002, <0.05). The instantly expanded flap contraction rates were 30.3 ± 0.8 and 32.3 ± 0.9 %, respectively for the two groups, and the difference was not statistically significant (p = 0.47, >0.05). We fitted a linear regression model that was Y = 0.533 − 0.003X, where Y was the contraction rate of the expanded flap and X was the period of expansion. The contraction rate of the expanded flap was negatively correlated with the period of expansion. CONCLUSIONS: Compared with the traditional method of implanting a single expander, the new method of overlapping two expanders in a single cavity increased the skin expansion rate. The instantly expanded flap contraction rate did not differ significantly between the two groups, so the amount of expanded skin area absolutely increased. The clinical application of the new method is worth promoting. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Soil acidification in a tailing area of ionic rare earth in Southeast China.

Ionic rare earth ores are now commonly mined using the ammonium sulfate in situ leaching method, causing soil acidification in tailings. To evaluate the degree of soil acidification in tailings and the influence of mining activities on acidification, we selected an ionic rare earth tailing and a nearby unmined area in Southeast China. This tailing had been closed for 12 years. We sampled the soil from the surface to the bedrock in layers and determined soil properties related to soil acidification. The results showed that the average soil pH was 5.0 in the unmined area and 4.5 in the mined area (tailing area). Rare earth mining led to a decrease in soil pH of 0.47 units per 10 years, which was 2-5 times higher than that of other land uses. The shallow soil acidification in the mined area is not affected by mining. Deep soils were significantly acidified and the H+ concentration in the soil solution was approximately nine times that of the unmined area soil. Deep soil acidification is influenced very little by natural factors. The average soil ammonium­nitrogen (NH4+-N) and nitrate­nitrogen contents in the mined area were 58.34 mg kg-1 and 8.19 mg kg-1, respectively, 84 times and 21 times that of the unmined area. There were large amounts of NH4+, NO3-, and H+ in the soil of the mined area, indicating that soil acidification is closely related to exogenous NH4+-N input and nitrogen transformation. Nitrification is the most important driver of soil acidification in mining areas. Continued nitrification of excess NH4+-N will continue to produce H+ and migrate with water, which will cause long-term harm to the soil and surrounding environment in the mining area. Therefore, it is necessary to remove the enriched NH4+-N in tailings soil to avoid further soil acidification.

Deep accumulation of soluble organic nitrogen after land-use conversion from woodlands to orchards in a subtropical hilly region.

Accumulation of soluble organic nitrogen (SON) in soil poses a significant threat to groundwater quality and plays an important role in regulating the global nitrogen cycle; however, most related studies have focused only on the upper 100-cm soil layers. Surface land-use management and soil properties may affect the vertical distribution of SON; however, their influence is poorly understood in deep soil layers. Therefore, this study assessed the response of SON concentration, pattern, and storage in deep regoliths to land-use conversion from woodlands to orchards in a subtropical hilly region. Our results showed that the SON stocks of the entire soil profile (up to 19.5 m) ranged from 254.5 kg N ha-1 to 664.1 kg N ha-1. Land-use conversion not only reshaped the distribution pattern of SON, but also resulted in substantial accumulation of SON at the 0-200 cm soil profile in the orchards compared to that in the woodlands (124.1 vs 190.5 kg N ha-1). Land-use conversion also altered the SON/total dissolved nitrogen ratio throughout the regolith profile, resulting in a relatively low (<50 %) ratio in orchard soils below 200 cm. Overall, 76.8 % of SON (338.4 ± 162.0 kg N ha-1) was stored in the layers from 100 cm below the surface to the bedrock. Regolith depth (r = -0.52 and p < 0.05) was found to be significantly correlated with SON concentration, explaining 17.8 % of the variation in SON, followed by total nitrogen (14.4 %), total organic carbon/total nitrogen ratio (10.1 %), and bulk density (9.3 %). This study provides insights into the estimation of terrestrial nitrogen and guidance for mitigation of groundwater contamination risk due to deep accumulation of SON.

Soil organic carbon content increase in the east and south of China is accompanied by soil acidification.

Increased soil organic carbon (OC) in China has been reported in the past two decades, suggesting the sequestration of atmospheric carbon dioxide into soil, mitigating climate change and improving soil health. On the other hand, soil pH decrease had also been reported nationwide. If the two are related, the strategy of increasing soil OC could negatively affect soil quality for food production and the environment. We investigate this thread based on large-scale soil survey data from two provinces with typical soil and cropping patterns in the east and south of China, Jiangsu (102,600 km2) and Guangdong (177,900 km2). The data include >5000 observations from soil surveys conducted over the past four decades, i.e., the 1980s, 2006-2007, and 2010-2011. Using spatiotemporal modelling, we show that across Jiangsu province, the topsoil OC on average has increased from 8.5 g kg-1 to 9.9 g kg-1 from 1980 to 2000 and a further increase to 12.6 g kg-1 in 2010. This increase was accompanied by a decrease in average pH from 7.63 to 6.90. In Guangdong, there was an overall increase in average topsoil OC content from 14.2 g kg-1, 16.5 g kg-1, and 20.2 g kg-1 with a decrease in average pH from 5.58, 4.90, and 4.98. Based on the spatiotemporal modelling results, the structural equation modelling analysis shows that OC and pH changes were significantly correlated and linked by increased soil N content. On croplands, soil N content was mainly attributed to N fertiliser application. The pH decrease was particularly significant in the east of China where the soils were neutral in pH. We recommend that more revolutionary means be taken to sequestrate atmospheric carbon into soil as the current OC increase due to increasing crop productivity via a high rate of nitrogen application may have a potential acidification effect.

Clinical implications and mechanism of histopathological growth pattern in colorectal cancer liver metastases.

Liver is the most common site of metastases of colorectal cancer, and liver metastases present with distinct histopathological growth patterns (HGPs), including desmoplastic, pushing and replacement HGPs and two rare HGPs. HGP is a miniature of tumor-host reaction and reflects tumor biology and pathological features as well as host immune dynamics. Many studies have revealed the association of HGPs with carcinogenesis, angiogenesis, and clinical outcomes and indicates HGP functions as bond between microscopic characteristics and clinical implications. These findings make HGP a candidate marker in risk stratification and guiding treatment decision-making, and a target of imaging observation for patient screening. Of note, it is crucial to determine the underlying mechanism shaping HGP, for instance, immune infiltration and extracellular matrix remodeling in desmoplastic HGP, and aggressive characteristics and special vascularization in replacement HGP (rHGP). We highlight the importance of aggressive features, vascularization, host immune and organ structure in formation of HGP, hence propose a novel "advance under camouflage" hypothesis to explain the formation of rHGP.

Soil acidification and loss of base cations in a subtropical agricultural watershed.

Soil acidification along with base cations loss degrades soil quality and is a major environmental problem, especially in agroecosystems with extensive nitrogen (N) fertilization. So far, the rates of proton (H+) production and real soil acidification (loss of base cations) remain unclear in subtropical agricultural watersheds. To assess the current status and future risk of soil acidification in subtropical red soil region of China, a two-year monitoring was conducted in a typical agricultural watershed with upland, paddy fields, and orchards where high N fertilizers are applied (320 kg N ha-1 yr-1). H+ production, neutralization and base cations losses were quantified based on the inputs (rainwater, inflow of water, and fertilizer) and outputs (outflow of water, groundwater drainage, and plant uptake) of major elements (K+, Ca2+, Na+, Mg2+, Al3+, NH4+, NO3-, SO42-, Cl-, and H+). The result showed that total H+ production in the watershed was 5152 molc ha-1 yr-1. N transformation was the most important H+ source (68%), followed by excess plant uptake of cations (25%) and H+ deposition (7%). Base cations exchange and weathering of minerals (3842 molc ha-1 yr-1) dominated H+ neutralization, followed by SO42- adsorption (1081 molc ha-1 yr-1), while H+ and Al3+ leaching amounted to 431 molc ha-1 yr-1, only. These results state clearly that despite significant soil acidification, the acidification of surface waters is minor, implying that soils have buffered substantially the net H+ addition. As a result of soil buffering, there was abundant loss of base cations, whose rate is significantly higher than the previously reported weathering rate of minerals in red soils (3842 vs 230-1080 molc ha-1 yr-1). This suggests that the pool of exchangeable base cations is being depleted in the watershed, increasing the vulnerability of the watershed, and posing a serious threat to future recovery of soils from acidification.

Nitrate runoff loss and source apportionment in a typical subtropical agricultural watershed.

Nitrate (NO3-) loss and enrichment in water bodies caused by fertilization are a major environmental problem in agricultural areas. However, the quantitative contribution of different NO3- sources, especially chemical fertilizers (CF) and soil organic nitrogen (SON), to NO3- runoff loss remains unclear. In this study, a systematic investigation of NO3- runoff and its sources was conducted in a subtropical agricultural watershed located in Yujiang County, Jiangxi Province, China. A semi-monthly sampling was performed at the inlet and outlet from March 2018 to February 2019. Hydrochemical and dual NO3- isotope (15 N and 18O) approaches were combined to estimate the NO3- runoff loss and quantify the contribution of different sources with a Bayesian isotope mixing model. Source apportionment by Stable Isotope Analysis in R (SIAR) suggested that NO3- in runoff was mainly derived from nitrification of ammonium (NH4+) mineralized from SON (37-52%) and manure/sewage (M&S) (25-47%), while the contribution of CF was relatively small (14-25%). The contribution of various sources showed seasonal variations, with a greater contribution of CF in the wet growing season (March to August). Compared with the inlet which contributed 37-40% to runoff NO3-, SON contributed more at the outlet (49-52%). Denitrification in the runoff was small and appeared to be confined to the dry season (September to February), with an estimated NO3- loss of 2.73 kg N ha-1. The net NO3- runoff loss of the watershed was 34.5 kg N ha-1 yr-1, accounting for 15% of the annual fertilization rate (229 kg N ha-1 yr-1). Besides M&S (22%), fertilization and remineralization of SON (CF + SON) were the main sources for the NO3- runoff loss (78%), suggesting accelerated nitrification of NH4+ from CF (24%) and SON mineralization (54%). Our study indicates that NO3- runoff loss in subtropical agricultural watersheds is dominated by nonpoint source pollution from fertilization. SON played a more important role than CF. Besides, the contribution of sewage should not be neglected. Our data suggest that a combination of more rational fertilizer N application (CF), better management of SON, and better treatment of domestic sewage could alleviate NO3- pollution in subtropical China.

Seasonal dynamics of soil pH and N transformation as affected by N fertilization in subtropical China: An in situ 15N labeling study.

Nitrogen (N)-induced soil acidification has received much attention worldwide. Nitrification and soil N mineralization are two key N cycle processes that affect soil acidification. However, the seasonal dynamics of soil pH under their combined influence is unclear. We studied the effect of N fertilization on soil pH and N transformations using 15N tracing in field lysimeters with soils developed from different parent materials (Quaternary red clay, sandstone, and basalt). Maize was planted with 200 kg N ha-1 yr-115N-labeled urea addition. During 7-45 days after fertilization, proton (H+) production due to nitrification of fertilizer N, nitrate (NO3-) leaching, and plant uptake exceeded H+ consumption by base cations mobilization and leaching, resulting in a significant soil pH decline. When nitrification activity decreased (after 45 days), due to exhausted ammonium (NH4+) availability, soil pH rose again. During the fallow period, acid neutralization due to base cation mobilization, and ammonification of soil organic N (SON) offset H+ production caused by nitrification of mineralized SON, leading to a sustained rise in soil pH. After the one-year experiment, no significant soil pH decrease was observed in any of the soils. Parent material had little effect on the seasonal dynamics of soil acidification, which appeared to be controlled by fertilization, environmental factors (temperature and moisture), and plant uptake. In subtropical regions, monitoring of soil pH on an annual basis may mask the effect of N fertilization on soil acidification.

Copper migration and isotope fractionation in a typical paddy soil profile of the Yangtze Delta.

To decipher Cu migration in paddy soils, which is important for understanding Cu supply in rice cultivation, Cu concentrations and isotope compositions were measured in a paddy soil profile in Suzhou, Eastern China, in the central Yangtze Delta. The results show that the variations in δ65Cu values and Cu concentrations are not coupled along the profile. From top to bottom, the δ65Cu values show small variations (0.07 ± 0.03‰ to 0.25 ± 0.01‰) in the upper layers (Ap-Br1), with a decrease in the subsurface Br2 layer (from 0.16 ± 0.04‰ to -0.19 ± 0.02‰), are almost homogeneous in the transitional Br3-BCrg layers (-0.01 ± 0.01‰ to -0.10 ± 0.02‰), and further decrease to -0.33 ± 0.01‰ in the permanently submerged G1 and G2 layers. Copper concentrations in the Ap layer show some fluctuations (25.8 to 29.0 µg/g), increase in the Br2 and Br3 layers (23.9 µg/g to 31.9 µg/g), and then decrease to 15.1 µg/g in the lower layers. The lack of coupling between δ65Cu values and Cu concentrations may be ascribed to various physicochemical conditions in different layers. In the upper layers, Cu(I) enriched in light isotopes migrates downward with soil solutions under flooded conditions, leaving the soils of the Ap and Br1 layers enriched in heavy Cu isotopes. In the Br2 layer, the readsorption of light Cu isotopes on clay minerals results in decreased δ65Cu values and increased Cu concentrations. In the Br3-BCrg layers, Cu(I) can be oxidized to Cu(II). The homogeneous Cu isotopes in these layers may mainly result from equilibrium adsorption of Cu on clay minerals. The decreased δ65Cu values and Cu concentrations in the G layer are mainly attributed to groundwater transport in this layer. This study represents the Cu isotope variations in a paddy soil profile and the possible mechanism of Cu isotope fractionation.