The contributions of socioeconomic and natural factors to the acid deposition over China

Highly efficient molecular film for inhibiting volatilization of hazardous nitric acid

Nitric acid, an important basic chemical raw material, plays an important role in promoting the development of national economy. However, such liquid hazardous chemicals are easy to cause accidental leakage during production, transportation, storage and use. The high concentration and corrosive toxic gas generated from decomposition shows tremendous harm to the surrounding environment and human life safety. Therefore, how to inhibit the volatilization of nitric acid and effectively control and block the generation of the toxic gas in the first time are the key to deal with the nitric acid leakage accident. Herein, a new method of molecular film obstruction is proposed to inhibit the nitric acid volatilization. The molecular film inhibitor spontaneously spread and form an insoluble molecular film on the gas-liquid interface, changing the state of nitric acid liquid surface and inhibiting the volatilization on the molecular scale. The inhibition rate up to 96% can be achieved below 45 °C within 400 min. Cluster structure simulation and energy barrier calculation is performed to elucidate the inhibition mechanism. Theoretical analysis of energy barrier shows that the specific resistance of the inhibitor significantly increased to 460 s·cm-1 at 45 °C, and the generated energy barrier is about 17,000 kJ·mol-1, which is much higher than the maximum energy required for nitric acid volatilization of 107.97 kJ·mol-1. The molecular film obstruction strategy can effectively inhibit the volatilization of nitric acid. This strategy paves the way for preventing the volatilization of liquid hazardous chemicals in accidental leakage treatment.

Unregulated GmAGL82 due to Phosphorus Deficiency Positively Regulates Root Nodule Growth in Soybean

Nitrogen fixation, occurring through the symbiotic relationship between legumes and rhizobia in root nodules, is crucial in sustainable agriculture. Nodulation and soybean production are influenced by low levels of phosphorus stress. In this study, we discovered a MADS transcription factor, GmAGL82, which is preferentially expressed in nodules and displays significantly increased expression under conditions of phosphate (Pi) deficiency. The overexpression of GmAGL82 in composite transgenic plants resulted in an increased number of nodules, higher fresh weight, and enhanced soluble Pi concentration, which subsequently increased the nitrogen content, phosphorus content, and overall growth of soybean plants. Additionally, transcriptome analysis revealed that the overexpression of GmAGL82 significantly upregulated the expression of genes associated with nodule growth, such as GmENOD100, GmHSP17.1, GmHSP17.9, GmSPX5, and GmPIN9d. Based on these findings, we concluded that GmAGL82 likely participates in the phosphorus signaling pathway and positively regulates nodulation in soybeans. The findings of this research may lay the theoretical groundwork for further studies and candidate gene resources for the genetic improvement of nutrient-efficient soybean varieties in acidic soils.

Soil acidification and salinity: the importance of biochar application to agricultural soils

Soil acidity is a serious problem in agricultural lands as it directly affects the soil, crop production, and human health. Soil acidification in agricultural lands occurs due to the release of protons (H+) from the transforming reactions of various carbon, nitrogen, and sulfur-containing compounds. The use of biochar (BC) has emerged as an excellent tool to manage soil acidity owing to its alkaline nature and its appreciable ability to improve the soil's physical, chemical, and biological properties. The application of BC to acidic soils improves soil pH, soil organic matter (SOM), cation exchange capacity (CEC), nutrient uptake, microbial activity and diversity, and enzyme activities which mitigate the adverse impacts of acidity on plants. Further, BC application also reduce the concentration of H+ and Al3+ ions and other toxic metals which mitigate the soil acidity and supports plant growth. Similarly, soil salinity (SS) is also a serious concern across the globe and it has a direct impact on global production and food security. Due to its appreciable liming potential BC is also an important amendment to mitigate the adverse impacts of SS. The addition of BC to saline soils improves nutrient homeostasis, nutrient uptake, SOM, CEC, soil microbial activity, enzymatic activity, and water uptake and reduces the accumulation of toxic ions sodium (Na+ and chloride (Cl-). All these BC-mediated changes support plant growth by improving antioxidant activity, photosynthesis efficiency, stomata working, and decrease oxidative damage in plants. Thus, in the present review, we discussed the various mechanisms through which BC improves the soil properties and microbial and enzymatic activities to counter acidity and salinity problems. The present review will increase the existing knowledge about the role of BC to mitigate soil acidity and salinity problems. This will also provide new suggestions to readers on how this knowledge can be used to ameliorate acidic and saline soils.

Ameliorative effect of calcium poly(aspartic acid) (PASP-Ca) and calcium poly-γ-glutamic acid (γ-PGA-Ca) on soil acidity in different horizons

Soil acidification is a worldwide eco-environmental problem detrimental to plant growth and threatening food security. In this study, calcium poly(aspartic acid) (PASP-Ca) and calcium poly-γ-glutamic acid (γ-PGA-Ca) were obtained through cation exchange and used to mitigate soil acidity owing to high solubility and complexing capability. Three rates at 6.7, 13.4, and 20.1 g kg^-1, denoted as PASP-Ca1, PASP-Ca2, and PASP-Ca3, and γ-PGA-Ca (7.4 g kg^-1) were surface-applied and compared with conventional lime (CaCO₃, 2.5 g kg^-1) along with control in two soil layers (top soil 0-10 cm, subsoil 10-20 cm). After leaching, various soil properties and aluminum fractions were measured to assess their ameliorative performance and mechanisms. Although lime achieved the highest soil pH (6.91) in the topsoil followed by PASP-Ca and γ-PGA-Ca (pH: 5.57-6.33), it had less effect on subsoil increase (5.3) vs. PASP-Ca and γ-PGA-Ca (pH: 5.44-5.74). Surface-applied PASP-Ca demonstrated efficiency in elevating soil pH and reducing exchangeable acidity, mainly as exchangeable Al³⁺, whereas γ-PGA-Ca addition superiorly improved soil pH buffering capacity (pHBC). Moreover, PASP-Ca and γ-PGA-Ca addition improved organic carbon by 34.4-44.9%, available P by 4.80-20.71%, and cation exchange capacity (CEC) by 6.19-29.2%, thus greatly enhanced soil fertility. Ca²⁺ from polyAA-Ca promoted the displacement of exchangeable Al³⁺ or H⁺ from soil colloid, which were subsequently complexed or protonated and facilitated leaching. Additionally, the transformation into stable organo-aluminum fractions via complexation inhibited further hydrolysis. Under PASP-Ca or γ-PGA-Ca addition, the saturation of aluminum in cation exchange complex was reduced 2.91-7.81% compared to the control without addition amendments. Thus, PASP-Ca and γ-PGA-Ca can serve as potent ameliorants to alleviate soil acidity and aluminum toxicity for sustainable agricultural development.

Characteristics of dissolved N2O and indirect N2O emission factor in the groundwater of high nitrate leaching areas in northwest China

Numerous studies have demonstrated high concentrations of dissolved N₂O and indirect N₂O emission factors in groundwater affected by agriculture. However, the characteristics of seasonal and vertical dimensional difference in groundwater in high nitrate leaching areas are relatively lacking. We monitored the concentrations of dissolved and wellhead N₂O of 23 groundwater wells over a one year period to understand the seasonal characteristics of dissolved and wellhead N₂O concentrations and indirect N₂O emission factors (EF₅) of the shallow and deep groundwater in a high nitrogen leaching area and analyze the reasons for their differences. The mean dissolved N₂O concentration in groundwater was 9.71 (9.03) μg/L, which was 1.5-fold higher during the wet season relative to the dry season. Furthermore, the leaching of soil N₂O caused by rainfall and irrigation could be a pivotal factor affecting seasonal variation in the dissolved N₂O. Shallow wells were found to have higher dissolved and wellhead N₂O concentrations compared with deep wells in all seasons. The low wellhead N₂O concentrations during the dry season were attributed to the seasonal decrease of the groundwater table and dissolved N₂O concentrations. We concluded that indirect N₂O emission factors did not vary in the vertical dimension but were higher during the wet season than that during the dry season. In addition, the mean indirect N₂O emission factor in the groundwater was 0.025 %, which was one order of magnitude below the current IPCC value (0.25 %). Thus, we proposed that such a low indirect N₂O emissions factor could imply a low indirect N₂O emission potential in groundwater with high dissolved oxygen and nitrogen loads. Our study further indicated that seasonal differences in dissolved N₂O concentrations and indirect N₂O emission factors should be considered when estimating the potential emissions of dissolved N₂O in groundwater.

Spatial Distribution and Estimation Model of Soil pH in Coastal Eastern China

Soil pH is an essential indicator for assessing soil quality and soil health. In this study, based on the Chinese farmland soil survey dataset and meteorological dataset, the spatial distribution characteristics of soil pH in coastal eastern China were analyzed using kriging interpolation. The relationships between hydrothermal conditions and soil pH were explored using regression analysis with mean annual precipitation (MAP), mean annual temperature (MAT), the ratio of precipitation to temperature (P/T), and the product of precipitation and temperature (P*T) as the main explanatory variables. Based on this, a model that can rapidly estimate soil pH was established. The results showed that: (a) The spatial heterogeneity of soil pH in coastal eastern China was obvious, with the values gradually decreasing from north to south, ranging from 4.5 to 8.5; (b) soil pH was significantly correlated with all explanatory variables at the 0.01 level. In general, MAP was the main factor affecting soil pH (r = -0.7244), followed by P/T (r = -0.6007). In the regions with MAP < 800 mm, soil pH was negatively correlated with MAP (r = -0.4631) and P/T (r = -0.7041), respectively, and positively correlated with MAT (r = 0.6093) and P*T (r = 0.3951), respectively. In the regions with MAP > 800 mm, soil pH was negatively correlated with MAP (r = -0.6651), MAT (r = -0.5047), P/T (r = -0.3268), and P*T (r = -0.5808), respectively. (c) The estimation model of soil pH was: y = 23.4572 - 6.3930 × lgMAP + 0.1312 × MAT. It has been verified to have a high accuracy (r = 0.7743, p < 0.01). The mean error, the mean absolute error, and the root mean square error were 0.0450, 0.5300, and 0.7193, respectively. It provides a new path for rapid estimation of the regional soil pH, which is important for improving the management of agricultural production and slowing down soil degradation.

A brand new two-phase wet oxidation absorption system for the simultaneous removal of SO2 and NOX from simulated marine exhaust gas

Marine engine exhaust emissions are increasingly harmful to the natural environment and human health and must be controlled. A self-synthesized amide (BAD, C₁₂H₂₅NO) in the laboratory shows a strong absorption capacity of nitric acid and nitrous acid, which may solve the problem that only using chlorine-based oxidant as an absorbent cannot completely absorb or retain NO₂ produced by NO oxidation in previous studies. Based on Multiwfn and VMD (Visual Molecular Dynamics) program calculation, the formation mechanism of hydrogen bonds between BAD with nitric acid and nitrous acid was revealed by electrostatic potential (ESP) analysis and further confirmed by FT-IR (Fourier transform infrared spectroscopy) spectra research. Subsequently, simultaneous removal of SO₂ and NO_X from simulated flue gas was carried out by using NaClO/BAD as a two-phase composite absorbent, and the maximum removal efficiencies of SO₂ and NO_X were 98.9% and 86.6%, respectively. The recycling experiments and the engineering experiments showing that NaClO/BAD can solve the problem of absorption of NO₂, and it can be a promising composite absorbent in wet desulfurization and denitrification of marine engine exhaust gas in practical applications.

Organic-inorganic calcium lignosulfonate compounds for soil acidity amelioration

Soil acidification is a problem widely occurring worldwide, which severely threaten food security and agricultural sustainability. Calcium lignosulfonate (CaLS), a cheap and ecofriendly compound, is used for the first time to amend acid soil by utilizing its unique organic and inorganic functional moieties simultaneously. Both column leaching and incubation experiments were conducted to investigate the comparative effects of CaLS (four rates at 5, 10, 15, 20 g kg^-1) and compared with conventional amendments, including gypsum (5 g kg^-1), lignin (5 g kg^-1), L + G (each at 5 g kg^-1), and control. The soil pH, exchangeable acidity and base cations, organic carbon, and different Al fractions were determined to unravel the ameliorative performance and mechanism of the treatments. Regardless of application modes and dosages, the results demonstrated that CaLS incorporation significantly increased soil pH, exchangeable Ca²⁺, cation exchange capacity, and organic carbon and decreased the contents of exchangeable acidity, especially exchangeable Al³⁺. The ameliorative mechanism was that amendment material led to the displacement of H⁺ and Al³⁺ off soil colloids by Ca²⁺. These released H⁺ and Al³⁺ which complexed with lignosulfonate anions into soluble organo-Al were all quickly leached from the soil column. The CaLS addition enhanced the transformation of exchangeable Al³⁺ and low-to-medium organo-Al complexes into highly stable organically bound fractions and immobilized into the soil. The complexing of CaLS functional groups with Al³⁺ impeded Al³⁺ from undergoing hydrolysis to produce more H⁺. As an environmental-friendly material, CaLS can be a promising amendment for soil acidity and Al toxicity amelioration.

Soil moisture determines nitrous oxide emission and uptake

Soils are major sources and sinks of nitrous oxide (N₂O). The main pathway of N₂O emission is performed through soil denitrification; however, the uptake phenomenon in denitrification is overlooked, leading to an underestimation of N₂O production. Soil moisture strongly influences denitrification rates, but exact quantifications coupled with nosZ, nirK, and nirS gene analysis remain inadequately unaccounted for. In this study, a ¹⁵N-N₂O pool dilution (¹⁵N₂OPD) method was used to measure N₂O production rates under different soil moisture levels. Therefore, 20%, 40%, 60%, 80% and 100% soil water holding capacity (WHC) were used. The results revealed that N₂O uptake rates increased proportionally with soil moisture content and peaked at 80% WHC with 4.17 ± 2.74 μg N kg^-1 soil h^-1. The N₂O production and net emission rates similarly peaked at 80% WHC, reading at 32.50 ± 4.86 and 27.63 ± 3.09 μg N kg^-1 soil h^-1 during the incubation period (18 days). Soil moisture content increased the gene copy number of the nosZ, NH₄⁺ content, and denitrification potential in soil. N₂O uptake at WHC 80-100% was significantly greater than that at WHC 20-60%. It was attributed to a decrease in O₂ and the high NO₃^- concentration inhibition (> 50 mg N kg^-1 of soil NO₃^--N content). Principal components analysis (PCA) indicated that the number of nosZ genes was the major driver of N₂O uptake, especially nosZ clade II. Thus, the results of this study deepen our understanding of the mechanisms underpinning N₂O sources and sinks in soils and provide a useful gene-based indicator to estimate N₂O uptake.

Pathways of soil N2O uptake, consumption, and its driving factors: a review

Nitrous oxide (N₂O) is an important greenhouse gas that plays a significant role in atmospheric photochemical reactions and contributes to stratospheric ozone depletion. Soils are the main sources of N₂O emissions. In recent years, it has been demonstrated that soil is not only a source but also a sink of N₂O uptake and consumption. N₂O emissions at the soil surface are the result of gross N₂O production, uptake, and consumption, which are co-occurring processes. Soil N₂O uptake and consumption are complex biological processes, and their mechanisms are still worth an in-depth systematic study. This paper aimed to systematically address the current research progress on soil N₂O uptake and consumption. Based on a bibliometric perspective, this study has highlighted the pathways of soil N₂O uptake and consumption and their driving factors and measurement techniques. This systematic review of N₂O uptake and consumption will help to further understand N transformations and soil N₂O emissions.

Increasing media pH contribute to the absorption of boron via roots to promote the growth of citrus

Low pH is an important limiting factor for plant development in the south of China due to problems of acid red soil and boron (B) deficiency. Whereas, there is very limited information on the relationship between media pH and B distribution in plant, the physiological process changed by the interaction of pH and B in citrus growth also unclear. This experiment was conducted on trifoliate rootstock by employing two different concentrations of B (0 or 10 μM B) under three pH levels: pH 4, pH 5, and pH 6. Our results illustrate that low pH inhibite plant growth and cause oxidative stress in the roots, resulting in cell membrane injury. The increase of pH and B addition reduce the accumulation of ROS (O₂^.- and H₂O₂) by regulating the activity of Class Ⅲ peroxidases (CIII Prxs). Moreover, increased pH improves the internal circulation of B in plants and decrease the content of lignin and cellulose in cell wall (CW). In summary, our investigation demonstrated that the increase of pH in nutrient solution can accelerate the re-distribution of B by roots to promote citrus growth. The accumulation of B in roots can protect plants from the damage of ROS by regulating the activity of CIII Prxs as well as decrease the content of lignin and cellulose are to promotes roots elongation.

Improved Tolerance of Mycorrhizal Torreya grandis Seedlings to Sulfuric Acid Rain Related to Phosphorus and Zinc Contents in Shoots

Acid rain (AR) is an increasingly serious environmental problem that frequently occurs in Southern China with sulfuric acid rain (SAR) as the main type. SAR can negatively affect the growth and physiological properties of trees, but mycorrhizal associations may mitigate such detrimental effects. However, the mechanisms by which arbuscular mycorrhizal fungi control SAR-induced impacts on Torreya grandis plants remain unclear. A pot experiment was conducted on T. grandis seedlings, an economically important tree species in Southern China, in which inoculated and non-inoculated T. grandis seedlings were subjected to three simulated SAR regimes (pH of 5.6, 4.0, and 2.5, respectively) to examine the effects on the growth, osmotic regulation, and nutrient absorption of these seedlings. The results show that, although SAR had no effect on the accumulation of biomass, it significantly decreased the concentrations of proline and soluble protein, shoot Zn²⁺, P, K⁺, and Ca²⁺ concentrations, and the Fe²⁺ and Mn²⁺ concentrations of shoots and roots. Mycorrhizal inoculation, especially with Rhizophagus irregularis, significantly increased total biomass, proline concentration, and the Zn²⁺, P, and K⁺ concentrations in the shoots of T. grandis under lower pH conditions. Moreover, our findings suggest that the combination of root colonization, acid tolerance, and the concentrations of shoot-P, shoot-Zn²⁺, and root-Fe²⁺ of T. grandis jointly conferred mycorrhizal benefits on the plants under SAR conditions. Given the enhancement of the nutritional quality of T. grandis owing to mycorrhizal associations, inoculation with R. irregularis may be preferable for the culturing and management of these plants under acidic conditions.