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Over the last two decades, atmospheric sulfur dioxide (SO2) concentrations have decreased in air-polluted regions. However, this decrease was accompanied by a rise in cloud water acidity (pH), which remains below 5. With this change, gas-phase hydrogen peroxide (H2O2) exceeded SO2 in most of these regions. These conditions where SO2 < H2O2 occurred at Mt. Norikura (2770 m.a.s.l.) during the 1900s. Therefore, to reveal the aqueous-phase oxidation of SO2 by H2O2, the present study investigated the inorganic and organic major ions and Se concentrations in cloud water in addition to aerosols and concentrations of gas species including O3, NOx, and SO2 collected in cloud events at Mt. Norikura during the summer of 1999. Backward air trajectory analyses indicated that the (NH4)2SO4 and trace (NH4)HSO4 aerosols originated from industrial and metropolitan areas in southwest Japan. The cloud water pH was between 3.6 and 4.4. The aqueous-phase SO42−/NO3− ratio (1.2 ± 0.6) was lower than that of the early 1990s (2.2) and 1960s (> 10) in our observation site, which was due to power plant restrictions in Japan since the 1970s. The ion species concentrations in cloud water indicated that cloud acidification resulted from dissolution of gaseous HNO3 and SO2, whereas gaseous hydrochloric acid and organic acid had a minor contribution to the acidification. Significant losses of Cl− and Mg2+ were observed in some of the cloud water. The excess value of non-sea-salt sulfate (nss-SO42−) over NH4+ in cloud water implies the in-cloud oxidation of gaseous SO2 to aqueous SO42−. A Se tracer technique was used to conduct in-situ measurements of in-cloud SO42− production. The results showed that the in-cloud production varied in a range between 7 ± 2 and 41 ± 14%. This temporal variation might be due to ambient SO2 concentrations based on Henry’s law.

Organic fertilizers as partial substitutes for chemical fertilizers improve soil nitrogen (N) retention capacity. However, the relative importance of biotic and abiotic N immobilization at different levels of organic N substitution and the subsequent effects on N utilization in paddy soils are not well elucidated. To address these, a combination of 15N incubation experiments and pot experiments were conducted to investigate biotic and abiotic N immobilization features and their effects on N fertilizer fate under long-term different fertilization regimes in paddy soils in China. Test soils that had received chemical fertilization (NPK), chemical N was substituted with 30%, 50%, and 70% organic N (70 F + 30 M, 50 F + 50 M, and 30 F + 70 M, respectively), and no fertilization (control) for 36 years. The results revealed that both abiotic and biotic NH4+-N immobilization were enhanced under organic N substitution soils. The highest NH4+-N abiotic and biotic N immobilization was observed under 50 F + 50 M soil, significantly increasing by 195.5% and 51.4%, respectively, compared to the NPK soil. In contrast, only abiotic NO3−-N immobilization increased with rising organic substitution N proportions. N fertilizer utilization efficiency was significantly enhanced in 50 F + 50 M soil (36.7%) compared to the NPK soil (30.3%), which was primarily attributed to the enhanced N pool activity and N immobilization capacity. However, the N fertilizer residue rate was significantly higher in the 30 F + 70 M soil (23.6%) compared to the NPK soil (21.6%), largely attributed to the soil properties improvement. Our results suggest that N immobilization capacity and N fertilizer utilization can be optimized with a 50% organic substitution ratio in our studied soil–crop system.

Karstification forms tremendous karst carbon sinks in the Earth. Whether terrestrial higher plants can absorb and utilize bicarbonate, there is a key testimony that karst carbon sinks can be transformed into carbon sequestrations by terrestrial higher plants. The uptake and use of root-derived bicarbonate, photosynthesis, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase contents of Broussonetia papyrifera (Bp) and Morus alba L. (Ma) were measured. This study provides the most direct and primary evidence for the transformation using the bidirectional isotope tracer technique. The transformation may result from the synergism in the absorption and utilization of photosynthetic and nonphotosynthetic pathway, and simultaneously strengthen karst carbon sink and carbon sequestrations of plants, while it had no effect on photosynthetic CO 2 assimilation in leaves. Differences in the transformation result in the discrepancies of Bp and Ma in the adaptation to karst environments. Karst-adaptable plants can more regulate the entire carbon cycle.

This study aims to quantify enteric methane (CH4) emission and dry matter intake (DMI) in beef steers under two rotational grazing systems: (i) a mixture of cover crops (vetch + ryegrass + forage radish) (CC) and (ii) alfalfa and fescue pasture (AFP). Eighteen Hereford steers were divided into two groups (nine steers per group), assigned to either the CC or AFP. Methane emissions were measured using the SF6 tracer technique. The results showed that steers grazing CC produced 29% less CH4 in g/d compared to those on the AFP (119.1 vs. 167.1 g/d for CC and AFP, p < 0.05) and 36% less CH4 yield (4.3 vs. 6.7% of gross energy intake). However, average daily gain (ADG), DMI, and CH4 intensity (gCH4/kg ADG) did not significantly differ between treatments. The integration of CC in a cattle grazing system has the potential to reduce CH4 emissions by improving forage quality.

Cadmium (Cd) pollution poses a serious threat to freshwater ecosystems. The freshwater mussel Anodonta woodiana is increasingly used as a bioindicator for monitoring Cd pollution in aquatic environments. However, the primary routes of Cd accumulation in A. woodiana remain unclear, and the molecular regulatory mechanisms underlying Cd accumulation are poorly understood. To address these gaps, this study employed a novel stable isotope dual-tracer technique to trace Cd from water (waterborne 112Cd) and the green alga Chlorella vulgaris (dietary 113Cd) during the simultaneous exposure experiment. Comparative transcriptomic analysis was then conducted to characterize molecular responses in A. woodiana following Cd exposure. The results showed that although newly accumulated 112Cd and 113Cd increased with exposure concentration and duration, the relative importance of 112Cd (91.6 ± 2.8%) was significantly higher than that of 113Cd (8.4 ± 2.8%) (p < 0.05). Cd exposure induced differentially expressed genes primarily enriched in the metabolic processes, cellular processes, and/or the ubiquitin-mediated proteolysis pathway. Within the ubiquitin-mediated proteolysis pathway, TRIP12 (E3 ubiquitin-protein ligase TRIP12) and Cul5 (cullin-5) were significantly upregulated. The findings will provide critical insights for interpreting Cd biomonitoring data in freshwater environments using mussels as bioindicators.

This study aimed to clarify the scientific quantification of fertilizer nitrogen (N) uptake and utilization, its destination, and its residual distribution in the soil at a depth of 0–30 cm after biochar application using 15N tracer technology. The purpose was to provide a theoretical basis for developing a scientific application strategy for N fertilizer and biochar in irrigated farmland areas. Two levels of N fertilizer application were set up using the 15N labeling method in microareas of large fields: the regular amount of N fertilizer (N1: 300 kg·ha−1) and a reduction of N fertilizer by 15% (N2: 255 kg·ha−1). Further, three levels of biochar application were set up: no biochar (B0: 0 kg·ha−1), a low amount of biochar (B1: 10 × 103 kg·ha−1), and a medium amount of biochar (B2: 20 × 103 kg·ha−1). The tested biochar was derived from corn stover (maize straw). The natural abundance of 15N-labeled fertilizer N, the total N content of each aboveground organ, and the total N content of soil at a depth of 0–30 cm in a spring wheat field at maturity were determined, and the yield was measured in the corresponding plots. The proportion of 15N-labeled fertilizer N uptake by each organ of spring wheat and the soil N uptake was 20.60–35.32% and more than 64.68%, respectively. Moreover, the proportion of soil N uptake showed a decreasing trend with an increase in biochar application. The spring wheat N uptake and utilization rate, the residue rate in the soil at a depth of 0–30 cm, the total utilization rate, and the rate of loss of 15N-labeled fertilizer N ranged from 15.21% to 29.61%, 23.33% to 28.93%, 38.54% to 58.54%, and 41.46% to 61.46%, respectively. The spring wheat N fertilizer utilization rate, fertilizer N residue rate in soil, and total fertilizer N utilization rate all increased gradually with an increase in biochar application, except for the N loss rate, which decreased gradually. When N fertilizer reduction was combined with medium biochar (B2N2), the yield of spring wheat significantly improved, mainly due to an increase in the number of grains in spikes. Under this treatment, the number of grains in spikes of spring wheat was 41.9, and the yield reached 7075.54 kg·ha−1, which was an increase of 9.69–28.25% and 10.91–25.35%, respectively, compared with other treatments. Yield increased by up to 25.35%, and nitrogen loss decreased by 48.24% under the B2N2 treatment. Biochar application could promote the amount and proportion of fertilizer N uptake in various organs of spring wheat as well as in the soil at a depth of 0–30 cm. In this study, a 15% reduction in N fertilizer (255 kg·ha−1) combined with 20 × 103 kg·ha−1 biochar application initially helped achieve the goal of increasing spring wheat yield and N fertilizer uptake, as well as improving fertilizer N utilization, providing an optimal scientific application strategy for N fertilizer and biochar in the farmland of the irrigation area. These results substantiate the hypothesis that biochar application enhances spring wheat (Triticum aestivum L.) assimilation of fertilizer-derived nitrogen (15N) while concomitantly improving fertilizer nitrogen retention in the soil matrix, which could provide a sustainable framework for nitrogen management in irrigated farmlands.

Flow measurements in pipelines using slug tracer have proved highly accurate for turbulent flow. This study experimentally investigates the effectiveness of using a passive rotor on the accuracy of discharge measurements in sewer pipes based on a saline slug tracer technique. For this purpose, a saline injector stack was developed to help inject saline at selected injection points. A passive axial flow rotor was also proposed and encased in the injector stack to enhance the mixing of injected tracer with the transmitted downstream flow and to decrease the required minimum mixing length. It was found that adding the passive rotor significantly increased the accuracy of the flow measurements. Two tracer flow formulas were developed: one based on the dimensional analysis approach and the other based on a semi-empirical formula obtained from the mass conservation approach. The resultant formulas compared favourably with flow metering, especially when utilizing the passive fan unit.

Background Iron nutrition is important for the health of women of reproductive age, and defining the physiologic requirement for iron can help them accurately plan the iron intake. However, research on the physiologic requirement for iron in women is insufficient worldwide. This study aimed to further improve the methodology and get more precise data for the physiological requirements for iron in women of reproductive age on the basis of our previous study. Method Sixty-one women of reproductive age who had not been pregnant before and during the whole study were included from Hebei province, China in 2015. Each subject participated in a 2-week metabolic trial with consuming 50 mg of the stable isotope 58 Fe, and were then followed for ~ 800 days. The abundance of 58 Fe and the total iron concentration in the circulation were measured using multi-collector inductively-coupled plasma mass spectrometry and atomic absorption spectroscopy. The physiologic requirement for iron in women of reproductive age was then calculated. Results The average iron circulation rate was 80.4%, and the steady period started from about 1 year. The average physiological requirement for iron of 21 subjects obtained by formula calculation was 1.55 mg/d and 23.63 μg.kg − 1 .d − 1 after adjustment for body mass, and that of 33 subjects obtained by linear regression was 1.29 mg/d, 20.98 μg.kg − 1 .d − 1 after adjustment for body mass. The results by two methods showed no significant difference. The EAR and RNI calculated from this results was 11–13 mg/d and 15–18 mg/d, respectively, both of which were slightly lower than the recommended value in Chinese Dietary Reference Intake (2013). Conclusion The physiological requirements for iron in women of reproductive age were in accordance with other studies, while the EAR and RNI calculated from which were slightly lower than Chinese present recommended value. Trial registration ChiCTR, ChiCTR-OCH-14004302 . Registered 14 February 2014, http://www.chictr.org.cn/enindex.aspx

During the process of circulating aquaculture, high concentrations of nitrate will accumulate. A simultaneous denitrification and fermentation process is described to remove nitrate from a recirculating aquaculture system using endogenous carbon on a biofilm. 15N isotope technology was used to assess the nitrate removal, mainly through heterotrophic denitrification. The nitrate removal rate could be as high as 98.97%, with a final concentration of nitrate below 1 mg/L. The denitrification process obeys a Michaelis–Menten-type enzyme kinetic model, with a half saturation constant of 99.91 mg/L and a maximum nitrate removal rate of 0.39 mg L−1 h−1 at 28 °C. The functional genes narG and narH for nitrate removal were obtained from Nitrospirae spp. at proportions of 39.13% and 26.16%, respectively. The acetate, propionate and iso-valerate produced by anaerobic fermentation provided the principal electron donors for denitrification.

Enteric methane (CH4) emissions from young ruminants contribute to a substantial proportion of atmospheric CH4 accumulation. Development of emission inventory and mitigation approaches needs accurate estimation of individual emission from animals under various physiological conditions and production systems. This research investigated the effect of different dietary concentrate contents on feed intake, growth performance, nutrient digestibility and CH4 emissions of heifers at various stages, and also developed linear or non-linear prediction equations using data measured by sulphur hexafluoride tracer technique. Increasing dietary concentrate contents increased feed intake and growth rate, enhanced nutrient digestibility, and reduced enteric CH4 emissions. Heifers at the age of 9, 12, and 15 months with an average weight of 267.7, 342.1, and 418.6 kg produced 105.2, 137.4, and 209.4 g/day of CH4, and have an average value of CH4 energy per gross energy intake (Ym) 0.054, 0.064, 0.0667, respectively. Equations relating CH4 emission values with animal and feed characteristics were developed with high determination coefficients for heifers at different growth stages. Dietary concentrate contents had significant influence on overall performance of heifers. These data can be used to develop regional or national emission inventories and mitigation approaches for heifers under various production regimes in China.