Improving liming mode for remediation of Cd-contaminated acidic paddy soils: Identifying the optimal soil pH, model and efficacies.

Liming has been widely taken to remediate Cd-contaminated acidic paddy soils, whereas liming mode involving in the relevant optimal soil pH, model and efficacies remain unclear. Both soil and field liming experiments were conducted to improve liming mode for precise remediation of Cd-contaminated acidic paddy soils. Soil batch liming experiments indicated soil DTPA-Cd and CaCl2-Cd were piecewise linearly correlated to soil pH with nodes of 6.8-8.0, and decreased respectively by 15.3%37.7% and 80.7%93.8% (P < 0.05) when soil pH raised over the nodes, indicating an appropriate target soil pH 7.0 for liming. Stepwise linear regression revealed that liming ratio (LR, kg ha-1) could be estimated from soil basal pH (pH0) and the interval to the target soil pH (ΔpH), as [LR=exp(1.10 ×ΔpH+0.61 ×pH0-4.98), R2 = 0.97, n = 42, P < 0.01]. The model exhibited high prediction accuracy (95.2%), low mean estimation error (-0.02) and root mean square error (0.20). Field liming experiment indicated liming to target pH decreased respectively soil CaCl2-Cd by 95.2-98.0% and rice grain Cd by 59.8-80.6% (P < 0.01), whereas uninfluenced rice grain yield. Correlation analysis and structural equation models (SEM) demonstrated that great reduction in Cd phytoavailability was mainly attributed to the transformation of soil water-soluble and exchangeable Cd to carbonate-bound Cd and Fe/Mn oxides-bound Cd and reduced Cd in iron plaque as increasing soil pH. However, rice grain Cd of 50% samples met national food safety standards limit of China (0.2 mg kg-1) due to the high soil Cd level (0.8 mg kg-1). In conclusion, liming to target soil pH 7.0 could be considered as a precise and effective remediation mode for Cd-contaminated acidic paddy soils and complementary practices should be implemented for severe pollution. Our results could provide novel insights on precise liming remediation of Cd-contaminated acidic paddy soils.

Phytoavailability of cadmium in rice amended with organic materials and lime: Effects of rhizosphere chemical changes and cadmium sequestration in iron plaque.

Excessive Cd in rice grains produced with acidic paddy soil is receiving increasingly widespread attention because it endangers human health. Applying organic materials (OM) and lime (L) is a common technique used to reduce Cd concentration in grains (CdG). Nevertheless, the mechanism by which their simultaneous application affects the Cd phytoavailability in soilrice systems remains ambiguous. In the current study, we adopted a rhizobag pot culture test to explore the influences of single application of OM [rice straw (RS), milk vetch (MV)], L, and their co-utilization on Cd phytoavailability and the associated mechanisms. The results showed that the application of RS, MV, L, L + RS (LRS), and L + MV (LMV) significantly decreased CdG by 26.9%, 38.2%, 48.6%, 50.0%, and 53.0%, respectively. Fe plaque (IP) formation was not affected by these treatments; however, Cd sequestration in IP (CdIP) was significantly reduced. CdIP was significantly reduced by 18.3%, 23.6%, 43.8%, 33.1%, and 41.4%, after RS, MV, L, LRS, and LMV treatments, respectively. Additionally, available Cd concentrations in rhizospheric soil (RHS) were significantly reduced by 11.5%, 14.8%, 15.1%, and 18.4%, after MV, L, LRS, and LMV treatments, respectively. Cd availability in RHS was significantly influenced by pH, dissolved organic carbon concentration, and Zn, Fe, and Mn availability. The results of the structure equation mode showed that CdG was mainly affected by CdIP, followed by Cd availability and the pH of RHS. In conclusion, the reduction of CdG by OM, L, and their co-utilization was the results of their combined effects of reducing Cd availability in RHS, CdIP, and Cd uptake by the roots. This study emphasizes that the reduction of CdG is a result of the dual effects of reducing Cd availability in RHS and CdIP after amendments application. L application alone or in conjunction with OM is an efficient practice to reduce CdG in acidic Cd-contaminated paddy fields.

Fe fortification limits rice Cd accumulation by promoting root cell wall chelation and reducing the mobility of Cd in xylem.

Fe biofortification and Cd mitigation in rice is essential for human health, thus the effects of fertilization with Fe on Cd uptake and distribution in rice need to be comprehensively studied. In this study, we investigated the roles of root iron (Fe)/manganese (Mn) plaques, root cell wall, organic acid, and expressions of Cd-transport related genes in restricting Cd uptake and translocation. The rice plants were exposed to 1 µM CdCl2 with or without the addition of three doses of Fe at 5, 50, and 500 µM EDTA-Na2Fe. The results showed that increasing supply of Fe remarkably reduced Cd accumulation in the shoots, mainly because of inhibited translocation of Cd from roots to shoots. As compared to 5 µM Fe treatment, 500 µM Fe significantly increased the ionic soluble pectin (ISP) content and decreased citric acid (CA) in the roots, thereby providing more Cd-binding sites in the cell wall of roots and reducing the mobility of Cd in xylem. Plant Fe status-mediated CA act as the main chelator for Cd mobilization, rather than through decreasing the pH. However, the plants supplied with low Fe or excess Fe facilitated the uptake of Cd in rice roots, as low Fe up-regulated the expression of Cd-transport related genes and excess Fe enhanced Cd enrichment on the root by iron plaque. Importantly, soil fertilization with Fe strongly reduced Cd accumulation in rice grain. Thus, optimizing the soil environmental Fe could effectively reduce Cd accumulation in the shoots by immobilizing Cd in the roots.

Influences of different source microplastics with different particle sizes and application rates on soil properties and growth of Chinese cabbage (Brassica chinensis L.).

The potentially negative effects of microplastics (MP) on agroecosystems have raised worldwide concerns. However, little is known about the negative effects of MP exposure on the soil-plant system. To fill up this knowledge gap, a pot experiment was set up, and two different MP types [high density polyethylene (HDPE) and general purpose polystyrene (GPPS)] were used, which had four particle sizes (<25, 25-48, 48-150, and 150-850 µm) at four application rates (2.5, 5, 10, and 20 g MP kg-1 soil). Some soil properties and the growth of Chinese cabbage (Brassica chinensis L.) were monitored. The results showed that (1) MP application with high application rates and relatively small particle sizes significantly enhanced the soil urease activity, which accompanied with enhanced soil pH and decreased soil available concentrations of phosphorus and potassium in some cases. (2) The exposure of MP did not significantly affect the activity of soil catalase regardless of their application rates and sizes. MP with different application rates and small sizes significantly reduced the soil sucrase activity, but the largest size of MP enhanced the activity of soil sucrase. (3) GPPS at 10-20 g kg-1 or with the sizes of <25 and 48-150 µm significantly reduced the fresh weight of Chinese cabbage, but the addition of HDPE had no remarkable effects on the fresh weight regarding of its application rates or sizes. (4) MP with high application rates and large sizes enhanced but small sizes of MP reduced the leaf soluble sugar concentration. The increasing application rates of MP and small size HDPE significantly reduced the starch concentration in the leaves of Chinese cabbage, however, the different sizes of GPPS showed limited effects on the leaf starch. The addition of MP with increasing application rates and different sizes always reduced the concentration of leaf chlorophyll. These parameters regarding to plant and soil could be used to assess the risks of MP pollution in the soil-plant systems. We found that the risks resulting from MP pollution were MP type-dependent and particle size-dependent. These findings indicate that overaccumulation of MP in the agriculture may possess an ecology risk and will negatively affect the agricultural sustainability and the food safety.

Meta-analysis of the effects of liming on soil pH and cadmium accumulation in crops.

Increasing cadmium (Cd) contamination in agricultural fields has resulted in a higher risk of Cd accumulation in the food chain. Lime addition can mitigate soil acidification and reduce Cd accumulation in crops cultured in Cd-contaminated soil. To determine key factors controlling the outcomes of liming in reducing Cd accumulation and enhancing soil pH, we performed a meta-analysis using previously published data from field and pot experiments. The results indicated that the liming showed positive effect sizes on the soil pH but negative effect sizes on Cd accumulation in crops, indicating the addition of different lime materials could enhance soil pH and reduce Cd accumulation in crops. The effect sizes of liming on soil pH under pot experimental conditions were higher than that under field experimental conditions, however, the effect sizes of application types and amount of limes on soil pH did not significantly differ between their individual different levels. Under a low background value of soil pH, SOM, CEC and clay, the addition of limes showed a significantly higher effect size on soil pH when compared to their individual higher soil background value, suggesting that the lower background values of soil pH, SOM, CEC and clay might facilitate the outcomes of liming to enhance soil pH. The experiment patterns, crop types and lime application amounts showed a limit effect on the outcomes of liming to reduce the shoot and grain Cd concentrations in crops. The lime types only showed a significant effect size on the shoot Cd accumulation but not on the grain Cd accumulation, in which the CaCO3 had the highest effect size (absolute value, the same below) followed by Ca(OH)2 and CaO. The low soil background values of total Cd concentration and CEC content, but a high soil SOM background content might facilitate the outcomes of liming to reduce the shoot Cd concentration in crops. However, only the background value of soil clay content showed a significantly negative effect size on the grain Cd accumulation, where a high soil clay content had a higher effect size than a low soil clay content. These findings provide useful knowledge about the effects of experiment patterns, crop types, soil conditions, lime types and lime addition amounts on the efficiency of liming in enhancing soil pH and decrease crop Cd concentration.

Cadmium and arsenic availability in soil under submerged incubation: The influence of humic substances on iron speciation.

Humic substances (HSs), as electron shuttles, are associated with iron oxide transformation, yet the manner by which HSs affect Cd/As availabilities during this process under anaerobic conditions remains unclear. Two HSs (humic sodium, HA-Na, and biochemical fulvic acid, BFA) were applied at 0, 1, 2, and 4 gCkg-1 in a submerged incubation experiment. The dissolved, extractable and fractions of Cd/As and different iron oxides in soils were monitored. The addition of both HA-Na and BFA decreased the CaCl2-extractable Cd by 12.66-93.13%, and increased the KH2PO4-extractable As by 18.81-71.38% on the 60th day of incubation. The soil Eh and crystalline iron oxides (Fed) decreased, while amorphous iron oxides (Feo) and dissolved As increased after addition of both HSs. However, the two HSs had opposite effects on soil pH and dissolved Cd at the end of the incubation. HA-Na immobilized 19.47-85.99% more available Cd than did BFA over the incubation, although the extent of immobilization was similar with the maximum application rate on the 60th day. BFA mobilized 5.22-26.12% more available As than did HA-Na. XPS data showed that FeOOH decreased while the FeO component increased over the incubation. Correlation analysis and SEM showed that the reduction in the soil Eh and Fed and relative increase in Feo increased the available Cd, while decreased the available As. Consequently, the addition of HA-Na and BFA, particularly combined with flooding irrigation management, could effectively reduce the available Cd in Cd-contaminated soil. However, this method should be used with caution in As-contaminated soil.

Agronomic traits and ionomics influence on Cd accumulation in various sorghum (Sorghum bicolor (L.) Moench) genotypes.

Cd is a common pollutant that contaminates the ecological environment of soil-crop systems and threatens food security and human health. Sorghum (Sorghum bicolor (L.) Moench) has a great potential for use as energy feedstock and Cd phytoremediation. Therefore, the identification of sorghum genotypes with high Cd accumulation is of great significance to Cd pollution remediation and production of bioenergy. A total of 126 biomass sorghum genotypes grown in a Cd-polluted field were investigated, and their agronomic traits were analyzed, including plant height, leaf number, shoot dry weight (SDW), soil and plant analyzer development (SPAD) value, and concentration of metal ions at seedling stage. Plant height was an important factor for screening potential biomass sorghum species because it presented a significant correlation with the Cd concentration in shoots and SDW (P < 0.01). The highest and lowest Cd concentration in sorghum shoots were 7.88 and 0.99 mg kg-1, respectively. The Cd concentration presented a negative and significant correlation with Mn in sorghum shoots (r = -0.303, P < 0.01), which was in agreement with the results that sorghum species with high Cd concentrations have lower Mn concentrations. In the mature stage, sorghum 12530 presented higher Cd concentration and dry weight in shoots compared with other genotypes. In summary, plant height, SDW, and concentration of Mn in sorghum shoots are critical parameters that synthetically influence the accumulation of Cd in sorghum shoots.

Increasing soil moisture faciliates the outcomes of exogenous sulfate rather than element sulfur in reducing cadmium accumulation in rice (Oryza sativa L.).

Cadmium (Cd) contamination in paddy soils and the related pollution risk of rice grain have received increasing attention. Agronomic measures, such as the application of sulfur and changes in water regimes, were reported to mitigate the accumulation of Cd in rice. However, there is limited information on the combined effects of sulfur application and water regimes. Therefore, a pot experiment was conducted to investigate the effects of two sulfur forms, three water regimes and multiple sulfur application rates on Cd accumulation in rice. The sulfur was applied as SO42- (SVI, replacing the traditional fertilizers by SO42--containing fertilizers), and element S (S0) was applied at 0, 10, 20, 30 and 40 mg S kg-1 soil. The water regimes were continuous flooding (F), flooding-moist alternation (FM), and moist irrigation (M), for a total of 30 treatments. The results indicated that application of SVI exceeding 30 mg S kg-1 significantly reduced the Cd concentrations in brown rice by 31.1-56.3%, and the Cd concentrations decreased with increasing amount of irrigation water. Similar reductions in Cd concentrations in rice shoots and rice straw collected at tillering and maturity stages were observed after application of SVI. However, the effect of S0 application on Cd accumulation in grain was not significant under different water regimes. Furthermore, this study found that application of both SVI and S0 inhibited the transfer of Cd from rice roots to shoots in most cases. These findings indicate that replacing traditional fertilizers with SO42--containing fertilizers, especially combined with increased irrigation, could be a potential approach to mitigate Cd accumulation in rice growing in Cd-contaminated acidic paddy soils.

A Novel Method with Stacking Learning of Data-Driven Soft Sensors for Mud Concentration in a Cutter Suction Dredger.

The dredger construction environment is harsh, and the mud concentration meter can be damaged from time to time. To ensure that the dredger can continue construction operations when the mud concentration meter is damaged, the development of a dredger with advantages of low price and simple operation that can be used in emergency situations is essential. The characteristic spare mud concentration meter is particularly critical. In this study, a data-driven soft sensor method is proposed that can predict the mud concentration in real time and can mitigate current marine mud concentration meter malfunctions, which affects continuous construction. This sensor can also replace the mud concentration meter when the construction is stable, thereby extending its service life. The method is applied to two actual construction cases, and the results show that the stacking generalization (SG) model has a good prediction effect in the two cases, and its goodness of fit R2 values are as high as 0.9774 and 0.9919, indicating that this method can successfully detect the mud concentration.

Foliar Application of Zn-EDTA at Early Filling Stage to Increase Grain Zn and Fe, and Reduce Grain Cd, Pb and Grain Yield in Rice (Oryza sativa L.).

The accumulation of Cd and Pb in rice grains poses a potential threat to human health, which is a subject of increasing concern across the globe. We examined the effect that foliar spraying of Zn-ethylenediaminetetraacetate (Zn-EDTA) (0.3% and 0.5% w/v) during the early-grain filling stage has on rice grain yield and Cd, Pb, Zn and Fe contents in rice tissues via a field experiment. The grain yield significantly decreased with the foliar application of 0.5% Zn-EDTA. In rice grain, foliar spraying of 0.5% Zn-EDTA significantly decreased the Cd and Pb contents, but increased the Zn and Fe contents. The main reasons for the decrease in the Cd and Pb content in grain were the inhibition of Cd and Pb by roots and the increased Fe content in grain via Zn-EDTA application. The foliar spraying of Zn-EDTA decreased the grain yield and Cd and Pb contents, while increased the Zn and Fe contents in grains.

Pim1 Overexpression Prevents Apoptosis in Cardiomyocytes After Exposure to Hypoxia and Oxidative Stress via Upregulating Cell Autophagy.

BACKGROUND/AIMS: Microvascular obstruction (MVO), an undesirable complication of percutaneous coronary intervention, is independently associated with adverse left ventricle remodeling and poor prognosis after acute myocardial infarction. Hypoxia and oxidative stress major roles in the pathophysiology of MVO. Pim1 serves an important protective role in the ischemic myocardium, but the underlying mechanisms remain poorly defined. Autophagy in early hypoxia or during moderate oxidative stress has been demonstrated to protect the myocardium. In this study, we investigated the association between the protective effect of Pim1 and autophagy after hypoxia and oxidative stress. METHODS: Ventricular myocytes from neonatal rat heart (NRVMs) were isolated. NRVMs were exposed to hypoxia and H2O2. Rapamycin and 3-methyladenine (3-MA) were used as an activator and inhibitor of autophagy, respectively. pHBAd-Pim1 was transfected into NRVMs. We assessed cardiomyocyte apoptosis by Annexin V-FITC/PI flow cytometry. Autophagy was evaluated by mRFP-GFP-LC3 adenovirus infection by confocal microscopy. Western blotting was used to quantify apoptosis or autophagy protein (caspase-3, LC3, P62, AMPK, mTOR, ATG5) concentrations. RESULTS: Autophagy and apoptosis in NRVMs significantly increased and peaked at 3 h and 6 h, respectively, after exposure to hypoxia and H2O2. The mTOR inhibitor rapamycin induced autophagy and decreased cardiomyocyte apoptosis, but the autophagy inhibitor 3-MA decreased autophagy and increased apoptosis at 3 h after exposure to hypoxia and H2O2. Pim1 levels in NRVMs increased at 3 h and decreased gradually after exposure to hypoxia and H2O2. Pim1 overexpression enhanced autophagy and decreased apoptosis. Pim1-induced promotion of autophagy is partly the result of activation of the AMPK/mTOR/ATG5 pathway after exposure to hypoxia and H2O2. CONCLUSION: Our results revealed that Pim1 overexpression prevented NRVMs from apoptosis via upregulating autophagy after exposure to hypoxia and oxidative stress, partly through activation of the AMPK/mTOR/ATG5 autophagy pathway.

Effectiveness of simultaneous applications of lime and zinc/iron foliar sprays to minimize cadmium accumulation in rice.

Due to the large area of Cd-contaminated paddy soils worldwide, low-cost measures to reduce the accumulation of Cd in rice plant are necessary. A field experiment was therefore conducted to investigate the reducing effect of lime combined with foliar applications of Zn (ZnSO4) or Fe (EDTA·Na2Fe) on Cd concentrations in brown rice on a Cd-contaminated paddy soil. The results indicated that liming alone or in combination with foliar sprays of Zn or Fe increased the soil pH by 0.27-0.63 units. However, limited effects of lime or lime combined with foliar applications of Zn/Fe on soil DTPA-extractable Cd, rice grain and rice straw biomass were observed. Liming alone significantly reduced the Cd concentration in brown rice and rice straw by 31.8% and 42.3%, respectively. The Cd concentrations in brown rice decreased by 25.5% and 65.4% and in rice straw by 53.0% and 68.1% after liming combined with foliar applications of Fe and Zn, respectively. In contrast, liming combined with foliar spraying of Fe significantly increased the transfer ratio of Cd from the rice straw to the grain. As a low-cost technique, lime application combined with foliar application of ZnSO4 could be recommended for the remediation of Cd-contaminated paddy soils.

Potential Involvement of MiR-30e-3p in Myocardial Injury Induced by Coronary Microembolization via Autophagy Activation.

BACKGROUND/AIMS: Coronary microembolization (CME) can lead to no-reflow or slow reflow, which is one of the important reasons for loss of clinical benefit from myocardial reperfusion therapy. MicroRNAs and autophagy are heavily implicated in the occurrence and development of almost all cardiovascular diseases. Therefore, the present study was designed to investigate the role of miR-30e-3p and autophagy in CME-induced myocardial injury rat model. METHODS: Sixty rats were randomly divided into six groups: sham, CME 1h,3h,6h,9h, and 12h (n = 10 per group). Our CME rat model was created by injecting polyethylene microspheres (42mm) into the left ventricle of the heart; the sham group was injected with same volume of normal saline. The cardiac function and serum cardiac troponin I (cTnI) level of each group was measured. HE staining and HBFP staining were used to evaluate the myocardial micro-infarction area of myocardium tissue samples. Then RT-qPCR and western blot were used to detect the expression of miR-30e-3p and, autophagy related protein LC3-II and p62, respectively. Transmission electron microscope (TEM) was used to identify autophagic vacuoles in tissue samples. RESULTS: The cardiac function of the CME 6h,9h, and 12h groups were significantly decreased compared to the sham group (P < 0.05) and the cTnI level in each group were also significantly increased (P < 0.05). The expression of miR-30e-3p in the CME 6h, 9h and 12h group were decreased significantly compared with the sham group (P < 0.05). Meanwhile, the expression of autophagy related protein LC3-II decreased significantly and p62 increased significantly in the CME 9h and 12h group (P < 0.05). TEM images showed typical autophagic vacuoles for each of the CME groups. CONCLUSIONS: Myocardial miR-30e-3p is down regulated after CME and is accompanied by inhibited autophagy and decreased cardiac function. Therefore, miR-30e-3p may be involved in CME-induced cardiac dysfunction by regulating myocardial autophagy.

Effects of Peanut Shell Biochar on the Adsorption of Cd(II) by Paddy Soil.

Soil from an experimental paddy field in southern China was incubated with peanut shell biochar to investigate effects of this additive on the adsorption and desorption characteristics of Cd(II) using batch methods. Incorporation of biochar increased adsorption of Cd(II) by the paddy soil at 20, 25, and 30°C; this trend was apparent both with increasing quantities of biochar and rising temperature. Incorporation of biochar primarily enhanced the non-electrostatic adsorption of Cd(II). In addition, supplementation with biochar decreased the adsorption rate of Cd(II), which decreased with increasing quantities of biochar. The Langmuir constant b and Freundlich constant kf both increased with greater quantities of biochar at different temperatures. Adsorption of Cd(II) was an endothermic process and occurred spontaneously. Incorporation of biochar decreased availability and mobility of Cd(II) to plants primarily through increased non-electrostatic adsorption of Cd(II) by paddy soil.

Phytoavailability of Cd and Pb in crop straw biochar-amended soil is related to the heavy metal content of both biochar and soil.

Crop straw biochar incorporation may be a sustainable method of amending soil, but feedstock-related Cd and Pb content is a major concern. We investigated the effects of heavy metal-rich (RC) and -free biochar (FC) on the phytoavailability of Cd and Pb in two acidic metalliferous soils. Biochar significantly increased soil pH and improved plant growth. Pb in soil and plant tissues significantly decreased after biochar application, and a similar pattern was observed for Cd after FC application. RC significantly increased NH4NO3-extractable Cd in both lightly contaminated (YBS) and heavily contaminated soils (RS). The Cd content of plants grown on YBS increased, whereas it decreased on RS. The Cd and Pb input-output balance suggested that RC application to YBS might induce a soil Cd accumulation risk. Therefore, identifying heavy metal contamination in biochar is crucial before it is used as a soil amendment.

Effect of coated urea on cadmium accumulation in Oryza sativa L. grown in contaminated soil.

Experiments were conducted to determine the effects of three types of coated urea on the accumulation of cadmium (Cd) in rice (Oryza sativa L.) grown in contaminated soil. Pot-culture experiments were conducted in a greenhouse from July to November 2012 on the rice cultivar "Hua Hang Si Miao" in Guangzhou (China). The experimental design was completely randomized with four treatments and three replications. The treatments were control (CK) (N 0 mg/kg), prilled urea (PU) (N 200 mg/kg), polymer-coated urea (PCU) (N 200 mg/kg), and sulfur-coated urea (SCU) (N 200 mg/kg). Our results indicated that applications of PCU and SCU slightly increased the dry weight of rice grains. The application of SCU significantly decreased the CaCl2 and toxicity characteristic leaching procedure (TCLP)-extractable Cd concentrations by 15.4 and 56.1%, respectively. Sequential extractions showed that PCU and SCU applications led to a significant decrease in Cd in the exchangeable fraction and an increase in the bound iron (Fe) and manganese (Mn) oxides fractions. Cd concentrations in grains treated with PCU were reduced by 11.7%, whereas SCU significantly reduced Cd concentrations by 29.1%. SCU reduced Cd transfer from the straws to the grain. Our results demonstrated that PCU and SCU may be effective in mitigating Cd accumulation in rice grown in acidic Cd-contaminated soil, especially in plants receiving SCU.

Changes in bacterial CO2 fixation with depth in agricultural soils.

Soils were incubated continuously in an atmosphere of (14)CO2 and the distribution of labeled C into soil organic carbon ((14)C-SOC) was determined at 0-1, 1-5, and 5-17 cm down the profile. Significant amounts of (14)C-SOC were measured in paddy soils with a mean of 1,180.6 ± 105.2 mg kg(-1) at 0-1 cm and 135.3 ± 47.1 mg kg(-1) at 1-5 cm. This accounted for 5.9 ± 0.7% and 0.7 ± 0.2%, respectively, of the total soil organic carbon at these depths. In the upland soils, the mean (14)C-SOC concentrations were 43 times (0-1 cm) and 11 times (1-5 cm) lower, respectively, than those in the paddy soils. The amounts of (14)C incorporated into the microbial biomass (MBC) were also much lower in upland soils (5.0 ± 3.6% and 2.9 ± 1.9% at 0-1 and 1-5 cm, respectively) than in paddy soils (34.1 ± 12.4% and 10.2 ± 2.1% at 0-1 and 1-5 cm, respectively). Similarly, the amount of (14)C incorporated into the dissolved organic carbon (DOC) was considerably higher in paddy soils (26.1 ± 6.9% and 6.9 ± 1.3% at 0-1 and 1-5 cm, respectively) than in upland soils (6.0 ± 2.7% and 4.3 ± 2.2%, respectively). The observation that the majority of the fixed (14)C-SOC, RubisCO activity and cbbL gene abundance were concentrated at 0-1 cm depth and the fact that light is restricted to the top few millimeters of the soil profiles highlighted the importance of phototrophs in CO2 fixation in surface soils. Phylogenetic analysis of the cbbL genes showed that the potential for CO2 fixation was evident throughout the profile and distributed between both photoautotrophic and chemoautotrophic bacteria such as Rhodopseudomonas palustris, Bradyrhizobium japonicum, Rubrivivax gelatinosus and Ralstonia eutropha.

Degradation kinetics and transformation pathway of methyl parathion by δ-MnO2/oxalic acid reaction system.

Methyl parathion (MP) is a typical organophosphorus pesticide that is widely used worldwide, and hydrolysis, oxidation and reduction are the main abiotic degradation processes. Manganese dioxide (MnO2) and organic acid can participate in various geochemical processes of pollutants, a reaction system was constructed to degrade MP using δ-MnO2 and oxalic acid. The δ-MnO2/oxalic acid reaction system could efficiently degrade MP, and the removal rate of MP (20 µM) reached 67.83% within 30 h under the optimized conditions (pH 5, [δ-MnO2] = 2 mM, [oxalic acid] = 100 mM). MP was hydrolyzed by substitution reactions of SN@P and SN@C, and reduced by conversion of the nitro groups (-NO2) in MP and its hydrolysates to amino groups (-NH2). The primary active substance produced in the reaction system was the complexes dominated by Mn(III)-oxalic acid. This study provides a scientific basis for the degradation of organophosphorus pesticides using MnO2 and an organic acid. The results have important theoretical significance and application value for pollution control and remediation of organophosphorus pesticides.

Foliar zinc reduced Cd accumulation in grains by inhibiting Cd mobility in the xylem and increasing Cd retention ability in roots1.

Cadmium (Cd) pollution endangers the safe utilization of paddy soils, and foliar zinc (Zn) can reduce the toxic effects of Cd. However, little is known about the effects of foliar Zn application on the transport and immobilization of Cd in key rice tissues and the physiological state of rice plants. A pot experiment was conducted to explore the effects of spraying 0.2% and 0.4% Zn (ZnSO4) during the early grain-filling stage on Cd transport in rice, photosynthesis, glutathione (GSH) levels, Cd concentrations in xylem sap, and the expression of Zn transporter genes. The results showed that grain Cd concentrations in the 0.2% Zn and 0.4% Zn treatments were 24% and 31% lower, respectively, than those of the control treatments at maturity. Compared with the control treatments, the 0.4% Zn treatment increased Cd by 60%, 69%, 23%, and 22% in husks, rachises, first internodes, and roots, respectively. Application of Zn reduced xylem Cd content by up to 26% and downregulated transporter genes (OSZIP12, OSZIP4, and OSZIP7a) in flag leaves. Foliar Zn increased Cd bioaccumulation in roots while decreasing Cd bioaccumulation in grains. Zn reduced GSH concentration in flag leaves and stems, inhibiting photosynthesis (intercellular CO2 concentration, transpiration rate). Taken together, foliar Zn can reduce the expression of Zn transporter genes and the mobility of Cd in the xylem, promoting the fixation of Cd in husks, rachises, first internodes, and roots, ultimately reducing Cd concentration in rice grains.

Key process for reducing grains arsenic by applying sulfate varies with irrigation mode: Dual effects of microbe-mediated arsenic transformation and iron plaque.

Sulfate affects the transformation of arsenic (As) in soil and its absorption by plant roots. However, the influence of sulfate and irrigation interactions on the mobility of As in the soil-rice system remains poorly understood. To address this gap, we conducted a pot experiment with varying sulfate levels and irrigation modes to examine their effects on rice As translocation, soil As forms, iron plaque formation, and microorganisms involved in As transformation. The addition of exogenous sulfate significantly reduced grain As levels by a maximum of 60.1%, 46.7%, and 70.5% under flooding (F), flooding-moist alternate (FM), moist (M) conditions, respectively. However, the changes in soil available As did not fully correspond to grains As content. Soil available As was only reduced by sulfate under the FM treatment, which limited grains As accumulation under this condition. The reduction in grains As content under F and M conditions was mainly attributed to sulfate-induced increases in soil pH, which in turn inhibited As translocation and promoted iron plaque formation. Additionally, both irrigation mode and sulfate fertilization independently or interactively influenced the abundance of Sulfuritalea, Koribacter, Geobacter, and Sulfuriferula, thereby affecting the As forms in soil through the Fe/S redox process. Specifically, under F and FM conditions, SO42--S inhibited Geobacter but stimulated Fe-oxidizing bacteria, possibly resulting in increased As bound to Fe/Mn oxides (As-F3). Under M condition, SO42--S levels regulated As adsorption and release through the participation of Fe/S cycle bacteria, specifically influencing the adsorbed As fraction (As-F2). Therefore, the addition of SO42--S hindered As translocation to grains by promoting As sequestration in the iron plaque and facilitating microbe-mediated As immobilization through the Fe/S cycle, which was dependent on soil moisture. These results can be used as a guide for sulfur fertilizer application under different soil moisture with the goal of minimizing rice grain As.