The adsorption-diffusion model and biomimetic simulation reveal the switchable roles of silicon in regulating toxic metal uptake in rice roots.

Soil contamination by heavy metals has become a serious threat to global food security. The application of silicon (Si)-based materials is a simple and economical method for producing safe crops in contaminated soil. However, the impact of silicon on the heavy-metal concentration in plant roots, which are the first line in the chain of heavy-metal entering plants and causing stress and the main site of heavy-metal deposition in plants, remains puzzling. We proposed a process-based model (adsorption-diffusion model) to explain the results of a collection of 28 experiments on alleviating toxic metal stress in plants by Si. Then we evaluated the applicability of the model in Si-mitigated trivalent chromium (Cr[III]) stress in rice, taking into account variations in experimental conditions such as Cr(III) concentration, stress duration, and Si concentration. It was found that the adsorption-diffusion model fitted the experimental data well (R2 > 0.9). We also verified the binding interaction between Si and Cr in the cell wall using SEM-EDS and XPS. In addition, we designed a simplified biomimetic device that simulated the Si in cell wall to analyze the dual-action switch of Si from increasing Cr(III) adsorption to blocking Cr(III) diffusion. We found that the adsorption of Cr(III) by Si decreased from 58% to 7% as the total amount of Cr(III) increased, and finally the diffusion blocking effect of Si dominated. This study deepens our understanding of the role of Si in mitigating toxic metal stress in plants and is instructive for the research and use of Si-based materials to improve food security.

Spatial variation in stability of wheat (Triticum aestivum L.) straw phytolith-occluded carbon in China.

Global climate warming, driven by human activities emitting greenhouse gases like CO2, results in adverse effects, posing significant challenges to human health and food security. In response to this challenge, it is imperative to enhance long-term carbon sequestration, including phytolith-occluded carbon (PhytOC). Currently, there is a dearth of research on the assessment and distribution of the stability of PhytOC. Additionally, the intricate relationships and effects between the stability and environmental factors such as climate and soil remain insufficiently elucidated. Our study provided a composite assessment index for PhytOC stability based on a rapid solubility assay and principal component analysis. The machine learning models that we developed in this study, utilize experimentally and publicly accessible environmental data on large spatial scales, facilitating the prediction and spatial distribution mapping of the PhytOC stability using simple kriging interpolation in wheat ecosystems across China. We compared and evaluated 10 common classification machine learning models at 10-fold cross-validation. Based on the overall performance, the Stochastic Gradient Boosting model (GBM) was selected as predictive model. The stability is influenced by dynamic and complex environments with climate having a more significant impact. It was evident that light and temperature had a significant positive direct relationship with the stability, while the other factors showed indirect effects on the stability. PhytOC stability exhibited obvious zonal difference and spatial heterogeneity, with the distribution trend gradually decreasing from the southeast to the northwest in China. Overall, our research contributed to reducing greenhouse gas emissions and achieving global climate targets, working towards a more sustainable and climate-resilient future.

Remobilization of Cd caused by iron oxide phase transformation and Mn2+ competition after stabilization by nano zero valent iron.

Stabilization techniques are vital in controlling Cd soil pollution. Nano zero valent iron (nZVI) has been extensively utilized for Cd remediation owing to its robust adsorption and reactivity. However, the environmental stress-induced stability of Cd after nZVI addition remains unclear. A pot experiment was conducted to evaluate the Cd bioavailability in continuously flooded (130 d) soil after stabilization with nZVI. The findings indicated that nZVI application did not result in a decline in Cd concentration in rice, as compared to the no-nZVI control. Additionally, nZVI simultaneously increased the available Cd concentration, iron-manganese oxide-bound (OX) Mn fraction, and relative abundance of Fe(III)-reducing bacteria, but it decreased OX-Cd and Mn availability in soil. Cadmium in rice tissues was positively correlated with the available Cd in soil. The results of subsequent adsorption tests demonstrated that CdO was the product of Cd adsorption by the nZVI aging products. Conversely, Mn2+ decreased the adsorption capacity of Cd-containing solutions. These results underscore the crucial role of both biotic and abiotic factors in undermining the stabilization of nZVI under continuous flooding conditions. This study offers novel insights into the regulation of nZVI-mediated Cd stabilization efficiency in conjunction with biological inhibitors and functional modification techniques.

Patterns and abiotic drivers of soil organic carbon in perennial tea (Camellia sinensis L.) plantation system of China.

Understanding soil organic carbon (SOC), the largest carbon (C) pool of a terrestrial ecosystem, is essential for mitigating climate change. Currently, the spatial patterns and drivers of SOC in the plantations of tea, a perennial leaf crop, remain unclear. Therefore, the present study surveyed SOC across the main tea-producing areas of China, which is the largest tea producer in the world. We analyzed the soil samples from tea plantations under different scenarios, such as provinces, regions [southwest China (SW), south China (SC), south Yangtze (SY), and north Yangtze (NY)], climatic zones (temperate, subtropical, and tropical), and cultivars [large-leaf (LL) and middle or small-leaf (ML) cultivars]. Preliminary analysis revealed that most tea-producing areas (45%) had SOC content ranging from 10 to 20 g kg-1. The highest SOC was recorded for Yunnan among the various provinces, the SW tea-producing area among the four regions, the tropical region among the different climatic zones, and the areas with LL cultivars compared to those with ML cultivars. Further Pearson correlation analysis demonstrated significant associations between SOC and soil variables and random forest modeling (RF) identified that total nitrogen (TN) and available aluminum [Ava(Al)] of soil explained the maximum differences in SOC. Besides, a large indirect effect of geography (latitude and altitude) on SOC was detected through partial least squares path modeling (PLS-PM) analysis. Thus, the study revealed a high spatial heterogeneity in SOC across the major tea-producing areas of China. The findings also serve as a basis for planning fertilization strategies and C sequestration policies for tea plantations.

Nitrogen addition increased soil particulate organic carbon via plant carbon input whereas reduced mineral-associated organic carbon through attenuating mineral protection in agroecosystem.

Nitrogen (N) addition can have substantial impacts on both aboveground and belowground processes such as plant productivity, microbial activity, and soil properties, which in turn alters the fate of soil organic carbon (SOC). However, how N addition affects various SOC fractions such as particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), particularly in agroecosystem, and the underlying mechanisms remain unclear. In this study, plant biomass (grain yield, straw biomass, and root biomass), soil chemical properties (pH, N availability, exchangeable cations and amorphous Al/Fe - (hydr) oxides) and microbial characteristics (biomass and functional genes) in response to a N addition experiment (0, 150, 225, 300, and 375 kg ha-1) in paddy soil were investigated to explore the predominant controls of POC and MAOC. Our results showed that POC significantly increased, while MAOC decreased under N addition (p < 0.05). Correlation analysis and PLSPM results suggested that increased C input, as indicated by root biomass, predominated the increase in POC. The declined MAOC was not mainly dominated by microbial control, but was strongly associated with the attenuated mineral protection (especially Ca2+) induced by soil acidification under N addition. Collectively, our results emphasized the importance of combining C input and soil chemistry in predicting soil C dynamics and thereby determining soil organic C storage in response to N addition in rice agroecosystem.

Nitrogen addition reduces phosphorus availability and induces a shift in soil phosphorus cycling microbial community in a tea (Camellia sinensis L.) plantation.

Nitrogen (N) and phosphorus (P) are two important nutrient elements that limit the growth of plants and microorganisms. The effect of the N supply on soil P cycling and its mechanism remain poorly known. Here, we characterized the effects of different N application rates on soil P availability, the abundances of P-cycling functional genes, and microbial communities involved in P-cycling following the application of N for 13 years in a tea plantation. Soil available P (AP) decreased significantly under N application. The opposite pattern was observed for the activity of soil phosphatases including alkaline (ALP) and acid phosphatase (ACP). Furthermore, N addition increased the abundance of ppa but decreased the abundance of phoD in soil. Both ppa- and phoD-harboring communities varied with N application levels. Redundancy analysis (RDA) showed that soil pH was a key variable modulating ppa-harboring and phoD-harboring microbial communities. Partial least squares path modeling (PLS-PM) revealed that long-term N application indirectly reduced soil P availability by altering the abundances of phoD-harboring biomarker taxa. Overall, our findings indicated that N-induced reductions in AP increased microbial competition for P by selecting microbes with P uptake and starvation response genes or those with phosphatases in tea plantation system. This suggests that tea plantations should be periodically supplemented with P under N application, especially under high N application levels.

Planting and mowing cover crops as livestock feed to synergistically optimize soil properties, economic profit, and environmental burden on pear orchards in the Yangtze River Basin.

BACKGROUND: Pears, as an important cash crop, are currently facing great issues due to unsustainable management practices. Cover cropping is a sustainable management strategy that can improve soil fertility and increase fruit yield, while it may also stimulate greenhouse gas emissions. Therefore, synergizing multiple indicators to achieve sustainable development is critical. This study introduces a new management system, namely the planting and mowing of ryegrass as a livestock feed system (PRSS), and analyzes its impact on soil quality, economic benefits, and environmental burdens. RESULTS: Our results indicated that PRSS could increase soil pH from 5.08 to 5.48 and decrease the content of soil alkali-hydrolyzable nitrogen, total phosphate, and available phosphate (26.96-59.89%) while also enhancing yield (+38.51%) compared with the traditional natural grass management system (TMS). The average soil methane fluxes in PRSS were 72.67 µg m-2 day-1 , higher than those of TMS (61.28 µg m-2 day-1 ). However, the gross primary production was lower than TMS (-37.24%), and no significant difference was observed in soil nitrous oxide fluxes. In different scenarios, the total profit of PRSS mode 1 (mowing ryegrass and selling to a livestock company) and PRSS mode 2 (mowing ryegrass and feeding own sheep) were 10 706.21 $ ha-1 and 26 592.87 $ ha-1 respectively. These values are respectively2.36 times and 5.85 times higher than that of TMS. The total global warming potential of TMS (18.19 t CO2 -eq ha-1 ) was 1.29 t CO2 -eq ha-1 higher and 2.89 t CO2 -eq ha-1 lower than that of PRSS mode 1 and mode 2 respectively. CONCLUSION: Compared with traditional natural grass, planting and mowing ryegrass in pear orchards can optimize soil properties, increase fruit yield, and reduce global warming potential. Different modes can greatly increase revenue but have varying impacts on environmental burdens. These findings can help rebuild the links between farmland and specialized livestock production, contributing to sustainable development in the pear industries. © 2023 Society of Chemical Industry.

Production of potassium-enriched biochar from Canna indica: Transformation and release of potassium.

Potassium (K) is one of the essential macronutrients for plant growth, while most agricultural soils are suffering from K deficiency worldwide. Therefore, it is a promising strategy to prepare K-enriched biochar from biomass waste. In this study, various K-enriched biochars were prepared from Canna indica at 300-700 °C by pyrolysis, co-pyrolysis with bentonite, and pelletizing-co-pyrolysis. The chemical speciation and release behaviors of K were investigated. The derived biochars showed high yields, pH values, and mineral contents, which were affected by the pyrolysis temperatures and techniques. The derived biochars contained a significant amount of K (161.3-235.7 mg/g), which was much higher than the biochars derived from agricultural residues and wood. Water-soluble K was the dominant K species in biochars with a proportion of 92.7-96.0%, and co-pyrolysis and pelletizing promoted the transformation of K to the exchangeable K and K silicates. In comparison with the C. indica derived biochars (83.3-98.0%), the bentonite-modified biochar showed a lower cumulative release proportion of K (72.5% and 72.6%) in a 28-day release test, meeting the Chinese National Standard for slow-release fertilizers. In addition, the pseudo-first order, pseudo-second order, and Elovich models well described the K release data of the powdery biochars, and the pseudo-second order model was the best fit for the biochar pellets. The modeling results indicated that the K release rate decreased after the addition of bentonite and pelletizing. These results indicated that the biochars derived from C. indica could be used as potential slow-release K fertilizers for agricultural application.

Sustainable strategies related to soil fertility, economic benefit, and environmental impact on pear orchards at the farmer scale in the Yangtze River Basin, China.

Pears are an important income source in China, and unreasonable management practices have had a negative impact on the sustainability of pear orchards. However, multi-objective synergistic strategies are unclear on a farmer scale. In this study, we quantified indicators of soil fertility (soil organic matter (SOM)), environmental impact (global warming potentials (GWP)), and economic benefit (ratio of benefit and cost (BCR)) and analysed the synergetic strategies based on survey data from 230 smallholders in the Yangtze River Basin (Shanghai City, Chongqing City, Zhejiang province, and Jiangxi province). The average SOM, GWP, and BCR were 28.9 g kg-1, 17.3 t CO2-eq ha-1, and 3.63, respectively. Furthermore, optimised solutions using the Pareto multiple-objective optimisation model can reduce the GWP by 44.6% and improve the SOM and BCR by 34.4% and 43.9%, respectively, when fertiliser N rate and density are both decreased and the ratio of organic fertiliser application is increased compared to farmer management practices. The structural equation model indicated that planting density and fertiliser N rate can directly influence GWP and indirectly increase SOM and BCR; organic fertiliser application directly affects the GWP, SOM, and BCR. Our research provides a bottom-up approach based on the farmer scale, which can improve the sustainability of pear systems, and these findings can be used as guidelines for policymakers and pear orchard managers.

Metagenomics reveals N-induced changes in carbon-degrading genes and microbial communities of tea (Camellia sinensis L.) plantation soil under long-term fertilization.

Soil organic carbon (SOC) is an important C pool of the global ecosystem and is affected by various agricultural practices including fertilization. Excessive nitrogen (N) application is an important field management measure in tea plantation systems. However, the mechanism underlying the impact of N fertilization on SOC, especially the microscopic mechanism remain unclear. The present study explored the effects of N fertilization on C-cycling genes, SOC-degrading enzymes and microbes expressing these enzymes by using a metagenomic approach in a tea plantation under long-term fertilization with different N rates. Results showed that N application significantly changed the abundance of C-cycling genes, SOC-degrading enzymes, especially those associated with labile and recalcitrant C degradation. In addition, the beta-glucosidase and chitinase-expressing microbial communities showed a significant difference under different N rates. At the phylum level, microbial taxa involved in C degradation were highly similar and abundant, while at the genus level, only specific taxa performed labile and recalcitrant C degradation; these SOC-degrading microbes were significantly enriched under N application. Redundancy analysis (RDA) revealed that the soil and pruned litter properties greatly influenced the SOC-degrading communities; pH and DOC of the soil and biomass and total polyphenol (TP) of the pruned litter exerted significant effects. Additionally, the random forest (RF) algorithm revealed that soil pH and dominant taxa efficiently predicted the beta-glucosidase abundance, while soil pH and DOC, pruned litter TP, and the highly abundant microbial taxa efficiently predicted chitinase abundance. Our study indicated that long-term N fertilization exerted a significant positive effect on SOC-degrading enzymes and microbes expressing these enzymes, resulting in potential impact on soil C storage in a perennial tea plantation ecosystem.

Long-term nitrogen addition increases denitrification potential and functional gene abundance and changes denitrifying communities in acidic tea plantation soil.

The response of soil denitrification to nitrogen (N) addition in the acidic and perennial agriculture systems and its underlying mechanisms remain poorly understood. Therefore, a long-term (12 years) field trial was conducted to explore the effects of different N application rates on the soil denitrification potential (DP), functional genes, and denitrifying microbial communities of a tea plantation. The study found that N application to the soil significantly increased the DP and the absolute abundance of denitrifying genes, such as narG, nirK, norB, and nosZ. The diversity of denitrifying communities (genus level) significantly decreased with increasing N rates. Moreover, the denitrifying communities composition significantly differed among the soils with different rates of N fertilization. Further variance partitioning analysis (VPA) revealed that the soil (39.04%) and pruned litter (32.53%) properties largely contributed to the variation in the denitrifying communities. Dissolved organic carbon (DOC) and soil pH, pruned litter's total crude fiber (TCF) content and total polyphenols to total N ratio (TP/TN), and narG and nirK abundance significantly (VIP >1.0) influenced the DP. Finally, partial least squares path modeling (PLS-PM) revealed that N addition indirectly affected the DP by changing specific soil and pruned litter properties and functional gene abundance. Thus, the findings suggest that tea plantation is a major source of N2O emissions that significantly enhance under N application and provide theoretical support for N fertilizer management in an acidic tea plantation system.

Acetamiprid fate in a sandy loam with contrasting soil organic matter contents: A comparison of the degradation, sorption and leaching of commercial neonicotinoid formulations.

The impacts of neonicotinoids have generally focussed on the responses of the pure active ingredient. Using a selection of two commercial formulations and the active ingredient, we ran three laboratory studies using 14C-labelled acetamiprid to study the leaching, sorption and mineralisation behaviours of the commercially available neonicotinoid formulations compared to the pure active ingredient. We added 14C-spiked acetamiprid to a sandy loam soil that had received long-term additions of farmyard manure at two rates (10 t/ha/yr and 25 t/ha/yr) and mineral fertilisers, as a control. We found significant differences in acetamiprid mineralisation across both the SOM and chemical treatments. Sorption was primarily impacted by changes in SOM and any differences in leachate recovery were much less significant across both treatment types. The mineralisation of all pesticide formulations was comparatively slow, with <23 % of any given chemical/soil organic matter combination being mineralised over the experimental period. The highest mineralisation rates occurred in samples with the highest soil organic matter levels. The results also showed that 82.9 % ± 1.6 % of the acetamiprid applied was leached from the soil during repeated simulated rainfall events. This combined with the low sorption values, and the low rates of mineralisation, implies that acetamiprid is highly persistent and mobile within sandy soils. As a highly persistent neurotoxin with high invertebrate selectivity, the presence of neonicotinoids in soil presents a high toxicology risk to various beneficial soil organisms, including earthworms, as well as being at high risk of transfer to surrounding watercourses.

Crop rotation stage has a greater effect than fertilisation on soil microbiome assembly and enzymatic stoichiometry.

Agronomic practises, such as fertilisation and crop rotation, affect soil microbial communities and functions. However, limited information is available regarding the relative importance of fertilisation and crop rotation stages in determining the soil microbiome and assembly processes. In addition, insights into the connections between the soil microbiome and enzymatic stoichiometry are scarce. In this study, soil samples were collected from a wheat-rice rotation system that received mineral and organic fertiliser inputs for 6 years to investigate soil microbiome assembly, and the relationship between the soil microbiome and enzymatic stoichiometry. Our results revealed that the crop rotation stage strongly affected the soil microbial community structure, assembly, and enzymatic functions compared to that of the fertilisation regime. Enzymatic stoichiometry results and vector analysis implied that mineral and organic fertilisation could alleviate the microbial N limitation. However, no-manure fertilisation led to microbial P limitation during the wheat stage. The decreases in soil pH mainly drove microbial P limitation due to the acidification induced by the mineral fertilisers. Microbial N/P limitation correlated more strongly with the bacterial assembly than with fungal assembly. Moreover, co-occurrence network analysis showed that ecological relationships between microbial taxa and enzymes were more complex during the wheat stage than that during the rice stage. Microbial nodes linked to acid phosphomonoesterase correlated significantly with the soil pH. Our study highlights the distinct responses of the soil microbiome to fertilisation in different crop-rotation stages, and provides novel insights into connections between microbial assembly and enzymatic stoichiometry.

Effect of planting and mowing cover crops as livestock feed on soil quality and pear production.

Introduction: The increasing demand for animal-products has led to an increasing demand for livestock feed. Using cover crop as green manure in orchards is an effective measure to improve fruit yield and quality. However, the effect of mowing cover forage crops as livestock feed on soil quality and crop production is unclear. Method: Therefore, a 4-year field experiment, which included two treatments, was conducted in pear orchards in Luniao County, China: natural grass (NG) and planting and mowing forage crop ryegrass as livestock feed (MF). Results: Under MF treatment, most soil nutrient content, especially alkalihydrolysable N (AN), total phosphate (TP), available phosphate (AP), and microbial biomass phosphate (MBP), had decreased significantly (P<0.05), while ß-D-glucosidase (BG, C-cycle enzyme) and soil C limitation at 10-20 cm depth and P limitation at subsoil (20-40 cm) was increased. In addition, the soil bacterial community component in topsoil (0-10 cm and 10-20 cm) and fungal community component in topsoil and subsoil were changed in the MF treatment. Network analysis showed that MF treatment had a lower edge number in topsoil but the community edge numbers increased from 12794 in NG to 13676 in MF in subsoil. The average weight degree of the three soil layers in MF treatment were reduced, but the modularity had increased than that in NG. For crop production, MF treatment was 1.39 times higher in pear yield and titratable acids (AC) reduced from 0.19% to 0.13% compared with NG. These changes were more associated with the indicators at the subsoil, especially for TP, AN, pH, and F-NMDS1 (non-metric multidimensional scaling (NMDS) axis 1 of fungi). Discussion: These results provide data support for the feasibility of planting and mowing forage crops as livestock feed on orchards as well as a new idea for the integration of crop and livestock.

Spraying high concentrations of chelated zinc enhances zinc biofortification in wheat grain.

BACKGROUND: Foliar application of highly concentrated ZnSO4 fertilizer improves Zn biofortification in wheat grains. However, excess ZnSO4 ·7H2 O concentration (≥5 g kg-1 , w v-1 ) has been associated with leaf burn and yield loss, necessitating Zn sources with a high threshold concentration. The aim of this study, based on a 2 year field experiment conducted on wheat cultivated in acidic and alkaline soil, was to identify a suitable Zn formulation with a high Zn concentration or efficient adjuvant to achieve optimal Zn biofortification levels without compromising agronomic performance. RESULTS: There was a continued increase in the Zn concentration in wheat grains and a decrease in grain yield with an increase in the concentration of the Zn foliar sprays in both soil types examined. Wheats treated with chelated Zn foliar sprays - Zn glycine chelate (ZnGly) and Zn-ethylenediaminetetraacetic acid (ZnEDTA) - had less foliar injury than those treated with unchelated Zn fertilizers. Furthermore, irrespective of wheat cultivars and soil types, ZnEDTA applied to wheat at a concentration of 10 g kg-1 achieved the highest grain Zn concentration without negatively affecting the wheat performance. Adjuvant type and concentration caused no significant variation in grain Zn concentration. CONCLUSION: Overall, without foliar burn, wheat treated with 10 g kg-1 ZnEDTA foliar spray had the best performance with regard to grain Zn concentration and grain yield, which could have considerable implications for Zn biofortification of wheat grain. © 2021 Society of Chemical Industry.

Glycine-chelated zinc rather than glycine-mixed zinc has lower foliar phytotoxicity than zinc sulfate and enhances zinc biofortification in waxy corn.

To determine whether high spraying concentrations of Zn sources increase the Zn concentration in waxy corn (Zea mays L. var. ceratina Kulesh) seeds without compromising agronomic performance, field experiments were conducted between 2018 and 2020. Excess ZnSO4 application caused foliar burn, barren ear tip, and grain yield loss. ZnEDTA and Glycine-chelated Zn (ZnGly) caused less foliar burn, but Glycine-mixed Zn caused more foliar burn than ZnSO4. The seed Zn concentration increased with spraying Zn concentration. ZnEDTA (≤0.8%) had a higher threshold concentration than ZnGly (≤0.4%). Nevertheless, Zn biofortification efficacy did not significantly differ between 0.4% ZnGly and 0.8% ZnEDTA, and the grain Zn recovery rate of 0.4% ZnGly was much higher than that of 0.8% ZnEDTA. Additionally, dual-isotope labelling tests confirmed that 15N-glycine and 68Zn in ZnGly interacted. In the future, chelating technology is essential for developing new Zn fertilizers to optimize Zn biofortification efficacy.

Nano zero-valent iron-induced changes in soil iron species and soil bacterial communities contribute to the fate of Cd.

Nano zero-valent iron (nZVI) is used for soil remediation; however, the impact of nZVI on soil solid iron phases and its interactions with soil microorganisms in relation to the fate of Cd in soil remains unclear. In the current study, we investigated the mechanisms underlying the change in mobility of Cd in exogenous Cd-contaminated soil with nZVI and γ radiation treatments. The results showed that nZVI treatment decreased Cd availability but also increased the soil pH and dissolved Mn and poorly crystalline Fe contents. However, the increased poorly crystalline Fe(II) levels contributed to a reduction in Cd availability in soils treated with nZVI by immobilizing Cd associated with Fe oxides, rather than by increasing pH or Mn oxide levels. Moreover, Cd stabilization efficiency was higher in γ-irradiated soils than in non-irradiated soils regardless of the Cd level, with noticeable differences in bacterial community composition between the non-irradiated and irradiated soils. The genera Bacillus, Pullulanibacillus, and Alicyclobacillus are important in the redox of poorly crystalline Fe(II)-containing minerals in non-irradiated soil. This research provides a new method for further improving the Cd stabilization efficiency of nZVI in combination with microbial iron oxidization inhibitors.

Poorly crystalline Fe(â ¡) mineral phases induced by nano zero-valent iron are responsible for Cd stabilization with different soil moisture conditions and soil types.

Nano zero-valent iron (nZVI) is a promising remediation material for Cd-contaminated soil, but questions remain regarding the effects of nZVI-induced Fe oxides on Cd availability with different soil types and moisture conditions. To identify the changes in Cd availability and Fe mineral phases resulting from the application of nZVI, three types of Cd-spiked soils with 0.1% nZVI amendment were incubated under different moisture conditions with water-holding capacities (WHCs) of 30%, 60%, and 180%. The availability of Cd was significantly decreased in yellow and black soils amended with nZVI, with fewer changes being observed in cinnamon soil. The limited effect of nZVI on Cd stabilization was due to the extremely low content of poorly crystalline Fe phases in cinnamon soil. The Cd stabilization efficiency of nZVI was higher in the flooding soils (180% WHC) than in the non-flooding yellow and black soils (30% and 60% WHC, respectively). Moreover, the addition of nZVI promoted the formation of less-available forms of Cd (Fe-oxide-bound Cd in yellow soil and Fe-oxide-bound and organic-material-bound Cd in black soil) under the flooding condition. The decrease in extractable Cd was strongly related to the increase in poorly crystalline Fe(Ⅱ) mineral phases among the three soils and various soil moisture contents. Although 0.1% nZVI amendment induced the dissolution of Mn oxides, it did not hinder the Cd stabilization in the three soils. Overall, this study indicates that increased amounts of poorly crystalline Fe(Ⅱ) compounds due to nZVI amendment play a critical role in the stabilization of Cd in soils.

Substrate control of sulphur utilisation and microbial stoichiometry in soil: Results of 13C, 15N, 14C, and 35S quad labelling.

Global plant sulphur (S) deficiency is increasing because of a reduction in sulphate-based fertiliser application combined with continuous S withdrawal during harvest. Here, we applied 13C, 15N, 14C, and 35S quad labelling of the S-containing amino acids cysteine (Cys) and methionine (Met) to understand S cycling and microbial S transformations in the soil. The soil microorganisms absorbed the applied Cys and Met within minutes and released SO42- within hours. The SO42- was reutilised by the MB within days. The initial microbial utilisation and SO42- release were determined by amino acid structure. Met released 2.5-fold less SO42- than Cys. The microbial biomass retained comparatively more C and S from Met than Cys. The microorganisms decomposed Cys to pyruvate and H2S whereas they converted Met to α-ketobutyrate and S-CH3. The microbial stoichiometries of C, N, and S derived from Cys and Met were balanced after 4 d by Cys-derived SO42- uptake and Met-derived CO2 release. The microbial C:N:S ratio dynamics showed rapid C utilisation and loss, stable N levels, and S accumulation. Thus, short-term organic S utilisation by soil microorganisms is determined by amino acid structure whilst long-term organic S utilisation by soil microorganisms is determined by microbially controlled stoichiometry.