Soil Iron Research Articles

Evaluation of inorganic phosphate solubilizing efficiency and multiple plant growth promoting properties of endophytic bacteria isolated from root nodules Erythrina brucei

BackgroundIn soils, phosphorous (P) mostly exists in fixed/insoluble form and unavailable for plants use in soil solution, hence it is in scarcity. P is fixed in the form of aluminium, iron and manganese phosphates in acidic soils and calcium phosphate in alkaline soils. Phosphate solubilizing bacteria, the ecological engineers play a pivotal role in the mobilization of fixed forms of P by using different mechanisms. The objectives of this study were to evaluate inorganic phosphate solubilizing efficiency and other multiple plant growth promoting traits of Erythrina brucei root nodule endophytic bacteria and to investigate effects of the selected endophytic bacteria on the growth of wheat plant under phosphorous deficient sand culture at greenhouse conditions.ResultsAmong a total of 304 passenger endophytic bacteria, 119 (39%) exhibited tricalcium phosphate (TCP) solubilization; however, none of them were formed clear halos on solid medium supplemented with aluminum phosphate (Al-P) or iron phosphate (Fe–P). Among 119 isolates, 40% exhibited IAA production. The selected nine potential isolates also exhibited potentials of IAA, HCN, NH3 and/or hydrolytic enzymes production. All the selected isolates were potential solubilizers of the three inorganic phosphates (Al-P, Fe–P and TCP) included in liquid medium. The highest values of solubilized TCP were recorded by isolates AU4 and RG6 (A. soli), 108.96 mg L−1 and 107.48 mg L−1, respectively at sampling day3 and 120.36 mg L−1 and 112.82 mg L−1, respectively at day 6. The highest values of solubilized Al-P and Fe–P were recorded by isolate RG6, 102.14 mg L−1 and 96.07 mg L−1, respectively at sampling days 3 and 6, respectively. The highest IAA, 313.61 µg mL−1 was recorded by isolate DM17 (Bacillus thuringiensis). Inoculation of wheat with AU4, RG6 and RG5 (Acinetobacter soli) increased shoot length by 11, 17.4 and 14.6%, respectively compared to the negative control. Similarly, 76.9, 69.2 and 53.8% increment in shoot dry weight is recorded by inoculation with RG6, AU4 and RG5, respectively. These nine potential endophytic isolates are identified to Gluconobacter cerinus (4), Acinetobacter soli (3), Achromobacter xylosoxidans (1) and Bacillus thuringiensis (1).ConclusionAU4, RG6 and RG5 can be potential bio-inoculants candidates as low cost agricultural inputs in acidic and/or alkaline soils for sustainable crop production.

Evaluation of the Iron-coating Technology for Direct-seeded Rice in the Philippines

Field and screenhouse experiments were conducted to evaluate the performance of iron-coated (Fe-coated) seeds in wet direct-seeded rice (DSR). Effects of iron-coating on seed germination and seedling establishment, yield performance, and the fate of added iron in rice and lowland soil were measured. The germination test disclosed that the mean maximum germination rates were almost similar between the coated and uncoated seeds across varieties, whereas the iron- coated seeds took a longer time to achieve the rates. Results confirmed that Fe-coated seeds produced more established seedlings at low seeding rates during the field experiment. Moreover, the effect of Fe-coating on yield was statistically similar to the transplanted rice and other wet direct seeding techniques, such as the use of dry and pre-germinated seeds regardless of the seeding rates and season. This implies that the seeding rate for wet DSR can be reduced using Fe-coated seeds without diminishing the yield. On the other hand, the screenhouse experiment disclosed a better seedling emergence response in the high flow rate with or without iron-coating. Though yields were not influenced by the treatments, the Fe-coated seeds at a static flow rate achieved the highest yield among the treatments using the NSIC Rc222 variety. Furthermore, Fe-coating in rice seeds did not increase the level of Fe in the soil and in the aboveground plant biomass under wet direct seeding practice. Therefore, the use of Fe-coated seeds is highly regarded both in the wet direct seeding and water seeding practices to reduce the seeding rate while sustaining or improving the yields that are normally achieved under the conventional wet direct seeding practice in the country.

Biofortification of iron in rice (Oryza sativa) grown in acid soil of Assam, India

A pot experiment was conducted during 2019 under rain protected condition at Assam Agricultural University, Jorhat to know the effect of two different levels of soil iron (Fe) content on Fe content of rice tissues including grain (brown rice). Soils of initial DTPA extractable Fe content of 159.40±0.51 mg/kg was applied with 50 ppm Ferrous sulfate solution to increase the soil Fe content to 182.35±0.57 mg/kg. Two popular rice varieties, Ranjit and Mahsuri, and one traditional variety Kajoli Chakua were cultivated as winter rice under submerged condition in pots. There was no Fe toxicity symptom in the leaves for the plants grown at two different soil Fe content. At harvesting stage, the concentration of Fe in different tissues of rice were detected in the order: leaves>husk>grain. The Fe content of brown rice was significantly higher (>100% than that of control) in plants grown in soils of higher Fe content. Significant variation in the Fe content of brown rice was observed according to its position on the rachis, being the highest at the top and the lowest at the bottom. Considering initial soil Fe status, application of Fe fertilizer of suitable concentration to the soil was found to be successful in biofortification of Fe in brown rice, leading to increase of Fe content depending on varieties.

Soil CO2 and CH4 fluxes from different forest types in tropical peat swamp forest

Information on temporal and spatial variations in soil greenhouse gas (GHG) fluxes from tropical peat forests is essential to predict the influence of climate change and estimate the effects of land use on global warming and the carbon (C) cycle. To obtain such basic information, soil carbon dioxide (CO2) and methane (CH4) fluxes, together with soil physicochemical properties and environmental variables, were measured at three major forest types in the Maludam National Park, Sarawak, Malaysia, for eight years, and their relationships were analyzed. Annual soil CO2 fluxes ranged from 860 to 1450 g C m⁻2 yr⁻1 without overall significant differences between the three forest sites, while soil CH4 fluxes, 1.2–10.8 g C m⁻2 yr⁻1, differed. Differences in GHG fluxes between dry and rainy seasons were not necessarily significant, corresponding to the extent of seasonal variation in groundwater level (GWL). The lack of significant differences in soil CO2 fluxes between the three sites could be attributed to set-off between the negative and positive effects of the decomposability of soil organic matter as estimated by pyrophosphate solubility index (PSI) and GWL. The impact of El-Niño on annual CO2 flux also varied between the sites. The variation in soil CH4 fluxes from the three sites was enhanced by variations in temperature, GWL, PSI, and soil iron (Fe) content. A positive correlation was observed between the annual CH4 flux and GWL at only one site, and the influence of soil properties was more pronounced at the site with the lowest GWL and the highest PSI. Variation in annual CH4 fluxes was controlled more strongly by temperature where GWL was the highest and GWL and plant growth fluctuations were the least. Inter-annual variations in soil CO2 and CH4 fluxes confirmed the importance of long-term monitoring of these at multiple sites supporting different forest types.

Differential metal sensing and metal-dependent degradation of the broad spectrum root metal transporter IRT1.

Iron is an essential micronutrient for plant growth and development. Under low iron conditions, Arabidopsis plants take up soil iron using the root iron transporter IRT1. In addition to iron, IRT1 also transports others divalent metals, including cadmium, which consequently accumulates into plant tissues and enters the food chain. IRT1 expression was shown to be regulated at the transcriptional and post-translational levels by its essential metal substrates to maximize iron uptake while limiting the accumulation of zinc, manganese, or cobalt. Here, we characterized the regulation of IRT1 by cadmium. A short-term exposure to cadmium decreased the cell surface levels of IRT1 through endocytosis and degradation, but with a lower efficiency than observed for other IRT1 metal substrates. We demonstrated that IRT1 endocytosis in response to cadmium is mediated through the direct binding of cadmium to histidine residues within the regulatory loop of IRT1. However, we revealed that the affinity of the metal sensing motif is much lower for cadmium compared to other metal substrates of IRT1. Finally, we proved that cadmium-induced IRT1 degradation takes place through ubiquitin-mediated endocytosis driven by the UBC35/36 E2 ubiquitin-conjugating enzymes and the IDF1 E3 ubiquitin ligase. Altogether, this work sheds light on the mechanisms of cadmium-mediated downregulation of IRT1 and provides an additional molecular basis for cadmium accumulation and toxicity in plants.

Vertical distribution and transformation of phosphorus and iron in paddy soils during the whole growth stage of rice

Paddy fields have alternating wet and dry hydrological cycles at different growth stages of rice, driving changes in soil environment and phosphorus (P) transformation and transport. In-situ measurements of dissolved oxygen (DO), iron (Fe), and P concentrations were conducted to determine the vertical distribution of these concentrations together with the hydrological and meteorological data during the whole growth stage. The results demonstrate that soil vertical DO concentrations at different growth stages were greatly influenced by the water level and temperature of the paddy field at the soil-water interface. A strong negative correlation between soil DO and DGT-labile Fe has been observed, whereas a strong positive correlation has been observed between soil Fe concentration and vertical P. In the paddy field, soil DO concentrations were lower during tillering, booting, and heading to flowering than during the other stages. Thus, soluble P fluxes from soil water interfaces (SWIs) to overlying waters were most significant during these three stages. Furthermore, soils in these three stages are capable of sustained release of P and are highly able to buffer P. Consequently, water management in paddy fields should take into account the hydrological environment during these three stages in order to minimize soil P release. The results of our study provide a valuable reference point for controlling soil P and Fe during rice growth.

Impact of Fortified Nano Zinc and Iron Composite Capsules on Growth, Yields and Nutrients Accumulation in Cabbage (Brassica oleracea var. capitata L.) and Cauliflower (Brassica oleracea var. botrytis L.)

Synthesized composites were characterized through UV-spectrophotometer, XRD, SEM, EDX and FTIR analysis. SEM and EDX images confirmed surface morphology of ordinary mesoporous nano silica (mNs) and Fe & Zn embedded mNs. In XRD pattern of mNs peaks absence indicate that nano silica synthesized by sol-gel method was amorphous whereas reduced graphene oxide (rGO) synthesized in crystalline form. FTIR spectra of Zn and Fe loaded mNs and rGO showed that encapsulation of zinc and iron by mNS and rGO was successful. Results of experiment indicate, twice foliar application of 60 ppm Zn+ 30 ppm Fe through mNs (T6) and 40 ppm Zn+20 ppm Fe through rGO (T8) exhibited significantly higher economic and biological yields of both crops over conventional and Control. With increasing doses of nano zinc and iron through mNs composite capsules, significant increase in nutrients content and uptake by cabbage and cauliflower was observed in comparison to control. Whereas, increasing doses of nano zinc and iron application through rGO lead to a considerable reduction in nutrient content and thus hamper their uptake. Thus, T6 and T8 treatments were best pronounced in terms of yields, nutrients uptake and enriching biomass by iron and zinc content in cabbage and cauliflower, respectively. Compared to control, quality of cabbage head and cauliflower curd biomass in terms of Fe and Zn content, protein and phenol content were significantly more with 40 ppm Zn+20 ppm Fe (T8) and 60 ppm Zn+30 ppm Fe (T6) through rGO and mNs , respectively. Available zinc and iron in soil was unaffected by application of zinc and Fe through mNs and rGO in crops.

Rice Tolerance to Iron-Deficient and Iron-Toxic Soil Conditions elucidate Mechanisms and Implications

Iron deficiency and iron toxicity are two contrasting soil conditions that significantly impact plant growth and development. Understanding the mechanisms underlying plant tolerance to these conditions is crucial for crop improvement and sustainable agriculture. This review discusses the physiological, biochemical, and molecular mechanisms employed by plants to tolerate iron-deficient and iron-toxic soil conditions. Key factors such as root morphological adaptations, iron uptake and transport systems, antioxidant defense mechanisms, and signaling pathways are explored in detail. Furthermore, the implications of elucidating these mechanisms for crop breeding and management strategies are discussed, emphasizing the importance of developing cultivars with enhanced tolerance to both iron-deficient and iron-toxic soils. Overall, this review provides insights into the complex interplay between plants and soil iron availability, highlighting avenues for future research and application in agricultural systems.

Coupled abiotic-biotic cycling of nitrous oxide in tropical peatlands.

Atmospheric nitrous oxide (N2O) is a potent greenhouse gas thought to be mainly derived from microbial metabolism as part of the denitrification pathway. Here we report that in unexplored peat soils of Central and South America, N2O production can be driven by abiotic reactions (≤98%) highly competitive to their enzymatic counterparts. Extracted soil iron positively correlated with in situ abiotic N2O production determined by isotopic tracers. Moreover, we found that microbial N2O reduction accompanied abiotic production, essentially closing a coupled abiotic-biotic N2O cycle. Anaerobic N2O consumption occurred ubiquitously (pH 6.4-3.7), with proportions of diverse clade II N2O reducers increasing with consumption rates. Our findings show that denitrification in tropical peat soils is not a purely biological process but rather a 'mosaic' of abiotic and biotic reduction reactions. We predict that hydrological and temperature fluctuations differentially affect abiotic and biotic drivers and further contribute to the high N2O flux variation in the region.

Bioresponses of earthworm-microbiota symbionts to polychlorinated biphenyls in the presence of nano zero valent iron in soil

Both earthworms and nano zero-valent iron (nZVI) have been recently regarded as important approaches for in-situ remediation of polychlorinated biphenyls (PCBs) in soil. However, the combined action of earthworms and nZVI toward PCBs, and the biological responses of earthworm-microbiota symbionts to nZVI-PCBs co-exposure in soil remediation systems remain unclear. In this study, a 28-d exposure with different levels of polychlorinated biphenyls (PCBs) and nZVI was applied to earthworm Eisenia fetida in an agricultural soil. Both physiological responses of earthworms and their surrounding microbiota in gut and soil were examined. Kinetic modelling parameters showed a doubled PCB accumulation in earthworms with the presence of nZVI. Meanwhile, nZVI-PCBs coexposure synergistically stimulated the activities of superoxide dismutase (SOD) and catalase (CAT), along with the elevated levels of reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione (GSH) in earthworms. Based on integrated metabolomic and 16S rRNA analysis, it was found that earthworms provided certain metabolites, e.g., S-(2-hydroxyethyl)glutathione, 16-hydroxypalmitic acid, and formamide, beneficial to PCB-degrading microbiota (Novosphingobium and Achromobacter) in the intestine. Our findings of nZVI-enhanced PCB bioaccumulation and the defense mechanism afforded by the earthworm-microbiota symbionts toward PCB-nZVI exposure show the promise of combining earthworms with nZVI for the remediation of PCBs-contaminated soil.

Exogenous iron alters uptake and translocation of CuO nanoparticles in soil-rice system: A life cycle study.

The abundant iron in farmland soil may affect the environmental fate of metal-based nanoparticles (MNPs). In this study, the effect of FeSO4 and nano-zero-valent iron (nZVI) as exogenous iron on the uptake and translocation of CuO nanoparticles (NPs) in soil-rice system was performed in a life cycle study. The results show that exogenous iron basically elevated the soil pH and electrical conductivity but lowered the redox potential. Moreover, the Cu bioavailability in soil was significantly increased by 86-269% with exogenous iron at the tillering stage, while was reduced by 15-45% with medium and high concentrations of Fe(II) at the maturation stage. Meanwhile, the addition of exogenous iron resolved the unfilling of grains caused by CuO NPs. Notably, except for highest Fe(II) treatment, both Fe(II) and nZVI reduced Cu accumulation from 31% to 84% in roots and leaves due to more iron plaque. Especially, medium Fe(II) level markedly decreased the Cu content in the brown rice. μ-XRF analysis suggests that high intensity of Cu was primarily located in the rice hull and embryo under Fe(II) treatment. The reduction of CuO NPs to Cu2O caused by Fe(II) can explain the positive effect of exogenous iron on controlling the environmental risk of MNPs.

Levels of Zinc (Zn), Copper (Cu), Iron (Fe), and Cadmium (Cd) in Soil, Rice Stalk, and Oryza Sativa Grain in Ishiagu Rice Field, Ebonyi State, Nigeria; Human Health Risk

Levels of heavy metals (Zn, Cu, Fe, Cd) were determined in soil, rice grain, and rice stalk from Federal College of Agriculture Ishiagu rice field, Ebonyi state, Nigeria. The dried samples were digested with a 1: 3 (HNO3: HCl) mixture and analyzed with atomic absorption spectrophotometer (AAS). The mean concentration of the metals in the soil before planting, soil after harvest, and rice grain were as follows: Zn (7.28, 11.33 and 24.90); Cu (3.40,4.64 and 4.14); Fe (803.04, 735.47 and 107.78); Cd (1.14, ND and ND) and were all within FEPA and FAO/WHO limits. The daily intake values for a 60 kg adult were Zn (0.04), Cu (0.01), and Fe (0.18) and were all below the recommended limits by Codex Alimentarius standards. The Target Hazard Quotient (THQ) for Zn, Cu, and Fe was less than one (1<), and the total hazard index was less than 1, indicating that the population will not be exposed to the potential health risk from these metals. However, the metal levels should be monitored to ensure they stay at harmless levels.

The Coffee Processing Method Had a More Pronounced Effect than Location and Production Systems on the Overall Quality of Kaffa Biosphere Reserve Coffees

A comprehensive examination of the physical and cup quality of Kafa Biosphere Reserve coffees was essential to identify the inherent qualities of the coffees in connection with the area’s soil physical and chemical characteristics. As a result, preliminary coffee quality data was acquired from bean physical and cup quality examination of coffees derived through a three-stage nested design combining districts (Gimbo, Gawata, and Decha), coffee production systems (forest, semiforest, and garden), and coffee processing methods (wet, semiwet, and dry). Representative soil samples were collected according to the sampling structure and analyzed following the standard procedures. Multiple factor analysis and Pearson’s correlation coefficient analysis were applied to the collected data. According to the results of multiple factor analysis, the Gimbo and Decha districts are not significantly different from each other in terms of coffee quality. However, they are substantially different from the Gawata district in terms of coffee quality. Similarly, within each district, there are no clear differences in coffee production systems. However, the production systems of districts varied significantly. The coffee processing method had a pronounced effect on the overall quality and preliminary grade, physical and raw quality variables of coffee. Screen retention (14) was correlated with soil iron, but it was related negatively to boron and sodium contents. A significant and positive relationship was observed between green coffee bean moisture content and soil potassium, calcium, magnesium, boron, sodium, organic carbon, silicon content, and soil pH. A positive and significant relationship between soil molybdenum and the coffee quality variable was observed across the studied districts whereas most soil micronutrients, specifically, zinc, sulfur, and manganese, were significantly and negatively related to the organoleptic qualities of the coffees. Further investigation that includes the effects of elevation is recommended in future studies.

Bioaccessibility of iron in pearl millet flour contaminated with different soil types

A controlled in-vitro experiment was conducted to determine the bioaccessibility of extrinsic soil iron in pearl millet contaminated with typical Malawian soils. Pearl millet was contaminated with soils at ratios typically encountered in real life. Iron concentrations of soil-contaminated flour increased such that soil-derived iron contributed 56, 83 and 91% of the total iron when the proportions of soil were 0.1, 0.5 and 1% (soil: grain w/w), respectively. When soils were digested alone, the concentration of bioaccessible iron differed depending on the type of soil. However, the concentration of bioaccessible iron in soil-contaminated flours did not exceed that of uncontaminated flour and there was no effect of soil type. This suggests that knowledge of the proportion of extrinsic soil iron in soil-contaminated grains would be useful for iron bioavailability estimations. Vanadium is a reliable indicator of the presence of extrinsic soil iron in grains and has potential applications in this regard.

Enhancement of Rose Scented Geranium Plant Growth, Secondary Metabolites, and Essential Oil Components through Foliar Applications of Iron (Nano, Sulfur and Chelate) in Alkaline Soils

Iron (Fe) deficiency exists as a widespread nutritional disorder in alkaline and calcareous soils; therefore, Fe-enriching strategies may be used to overcome this issue. Field experiments were conducted with a randomized complete design with three replicates for evaluating the effectiveness of iron oxide nanoparticles (Fe-NPs) against traditional Fe compounds (sulfate or chelate), which have various shortcomings on Rose-scented geranium (RSG) herb in terms of plant growth, phytopharmaceuticales, essential oil (EO), and its constituents. Supplementation of Fe-sources considerably improved RSG plant growth and EO yield in the 1st and 2nd cut throughout the two seasons over non-treated control plants. A total of 11 compounds of RSG-EO were identified; the main constituents were citronellol, geraniol, and eugenol. The results indicate that EO composition was significantly affected by Fe-sources. Amendments of Fe-sources considerably augmented photosynthetic pigments, total carbohydrates, nitrogen, phosphorous, potassium, iron, manganese, zinc, phenols, flavonoids, and anthocyanin. Commonly, Fe-NPs with humic acid (Fe-NPs-HA) supplementation was superior to that of traditional sources. The highest values were recorded with spraying Fe-NPs-HA at 10 mg L−1 followed by 5 mg L−1, meanwhile, the lowest values were recorded in untreated control plants. Current findings support the effectiveness of nanoparticle treatment over Fe-sources for improving growth and yield while also being environmentally preferred in alkaline soil. These modifications possibly will be applicable to EO quality and its utilization in definite food and in medical applications.

Simulation of Spatial Distribution Model of Some Micronutrients in Soil and Orange Tree Leaves Using Gaussian Model and GIS

ABSTRACT In the present study, spatial distribution model of iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) in soil and leaves of Dezful orange trees was simulated using Gaussian model and geographic information system (GIS) in 2019. Totally, 130 points were determined using global positioning system (GPS) and soil and leaf sampling was performed. Concentration of elements was measured by dry digestion and read by atomic absorption spectrophotometer. After initial statistical analysis of the data, level of correlation between variables measured in soil and leaves was calculated using Pearson's correlation coefficient test. Location of sampling points in Gaussian model was simulated by R software (Ricker’s Model). Data interpolation was performed using simple Kriging and Kernel methods, and interpolation accuracy was evaluated using baseline analysis of variance. Results of the study showed that mean squared error was equal to 0.153, 0.203, 0.145, and 0.161, respectively, for Fe, Zn, Cu, and Mn in soil using simple Kriging; and it was equal to 0.166, 0.153, 0.129, and 0.16, respectively, using Kernel method; and also mean squared error was obtained as 0.131, 0.158, 0.167, and 0.129, respectively, for leaf samples of orange trees using simple Kriging; and it was obtained as 0.229, 0.160, 0.14, and 0.17, respectively, using Kernel method. Finally, the values simulated by the model were implemented by GIS software. Results of semi-variogram obtained using Gaussian model showed that Gaussian statistics were suitable for modeling these elements in soil and leaf samples of orange trees. Our findings revealed that the model has good accuracy in predicting spatial distribution of these elements, and the current research has practical implications since, the model enables identification of areas with deficiencies and can be used in recommending fertilizer for the study area and similar areas.

Roles of soil active constituents in the degradation of sulfamethoxazole by biochar/persulfate: Contrasting effects of iron minerals and organic matter

The biochar/persulfate (BC/PS) has been extensively applied in the degradation of organic contaminants in the aqueous solutions. However, much less work has been done on the degradation of organic contaminants in soil by BC/PS, especially on the unclear roles of soil active constituents in the degradation. This study was conducted to investigate the degradation of sulfamethoxazole (SMX) in two soils through PS oxidation activated by biochar. Biochar was produced via the pyrolysis of peanut shell at 400 °C and 700 °C, which was denoted as BC400 and BC700, respectively. Two soils used were red soil and paddy soil, mainly differing in iron minerals and organic matter. Both biochar promoted SMX degradation (42.6 %–90.7 %) in two soils, compared to PS alone (20.9 %–41.7 %). In BC400/PS system, the free radicals were the dominant reactive species for SMX degradation, while the electron transfer pathway played a vital role in the SMX degradation by BC700/PS. Higher SMX degradation was observed in red soil (41.7 %–97.8 %) than that in paddy soil (20.3 %–94.8 %), which was ascribed to the promotion of iron minerals in red soil yet the inhibition of organic matter in paddy soil. Specifically, the reaction between ≡Fe(III)/≡Fe(II) and PS on the surface of iron minerals in red soil generated more SO4•− and •OH, resulting in the enhanced SMX degradation. However, the consumption of free radicals and suppression of electron transfer pathway by organic matter in paddy soil inhibited SMX degradation. As the comparative carbonaceous materials to biochar, graphite exerted no obvious degradation effect, whereas activated carbon exhibited the comparable promoting efficacy to BC700. Both biochar, especially BC700, significantly (p < 0.05) alleviated the adverse effects of PS treatment on wheat (Triticum aestivum L.) growth. Overall, this study demonstrates that biochar/persulfate was effective in SMX degradation in soil and the degradation was affected by soil iron minerals and organic matter, which should be paid more attention in the persulfate remediation of organic contaminated soils at a specific site.

Effects of Iron Rates on Growth and Development of Young Huanglongbing-affected Citrus Trees in Florida

Essential nutrients for citrus [‘Bingo’ (Citrus reticulata, Blanco)] production are important for different functions, including photosynthesis, resistance to disease, and productivity. During the past 15 to 20 years, citrus production in Florida has significantly declined as a result of the devastating citrus greening disease also called huanglongbing (HLB). Therefore, a greenhouse study was conducted for 2 years, starting in 2018, at the University of Florida/Institute of Food and Agricultural Sciences Citrus Research and Education Center in Florida to evaluate the effect of varying rates of iron on the growth and development of 2-year-old HLB-affected ‘Bingo’ (Citrus reticulata, Blanco) trees on Kuharske citrange rootstock. Four treatments were used in a randomized complete block (HLB status) design with seven single tree replicates for each treatment. The treatments applied were 0.0 (control), 5.6 (standard fertilization, lx), 11.2 (2x), and 22.4 (4x) kg⋅ha−1 iron on HLB-affected and healthy (non-HLB) citrus trees. Data including trunk diameter, tree height, and leaf samples were collected, processed, and analyzed at 3-month intervals for 2 years. At the end of the second year, trees were destructively sampled and processed as above-ground and below-ground biomass. Tree heights were different among iron rates of HLB-affected trees (P &lt; 0.001); however, they were similar for non-HLB trees for both years. Higher average trunk diameters (P &lt; 0.001) were observed for HLB-affected trees that received the 2x rate compared with the 1x rate and the control. In 2019, non-HLB trees showed 13% to 40% higher iron concentrations in leaves than HLB-affected trees. However, leaf iron concentrations were comparable for HLB-affected and non-HLB trees in 2020. Above-ground biomass for HLB-affected trees had between 33% and 44% more biomass (P &lt; 0.01) than below-ground biomass for the corresponding iron fertilization. Iron accumulation correlated positively with all studied nutrients in the above-ground parts for both HLB-affected and non-HLB trees. A 95% confidence interval at which total biomass was nearly maximum corresponded to an iron rate of 9.6 to 11.8 kg⋅ha−1, which was close to the 2x rate. Therefore, soil iron application using the aforementioned rates may be appropriate for better growth and development of young HLB-affected trees.

Structure characterization of Imidazolinone–Fe(II) complex by using multiple analytical and spectroscopic methods

Imazamox, one of imidazolinone herbicides, was found can chelate with Fe(II) in surface water enviroment to form imazamox-Fe(II) complex. By using EDS elemental analysis, HR-ESI-MS and JOB's curves, the complex was characterized as two molecule imazamox coordinated with one ferrous iron, besides, multiple analytical and spectroscopic methods, such as UV-vis, FT-IR, Raman and control experiments were conducted, the function group involved in coordination was determined, and the structure detail of imazamox-Fe(II) complex was proposed as four N atoms from two different imazamox ions (two N atoms from two pyridyl rings and the other two N atoms from two oxo-imidazole rings) and two O atoms from two different carboxylate groups to complete a 6-coordinate mode of Fe(II). Based on the finding, the influence of imidazolinone herbicides on available ferrous iron in soil was also discussed.

Spatial distribution of soil iron across different plant communities along a hydrological gradient in the Yellow River Estuary wetland

Iron is an important element and its biogeochemical processes are vital to the matter and energy cycles of wetland ecosystems. Hydrology greatly controls characteristics of soil property and plant community in wetlands, which can regulate the behavior of iron and its oxides. However, it remains unclear how the spatial distribution of iron and its forms in estuarine wetlands responses to hydrological conditions. Five typical plant communities along a naturally hydrological gradient in the Yellow River Estuary wetland, including Phragmites australis in freshwater marsh (FPA), Phragmites australis in salt marsh (SPA), Tamarix chinensis in salt marsh (TC), Suaeda salsa in salt marsh (SS) and Spartina alterniflora in salt marsh (SA), as sites to collect soil samples. The total iron (FeT) and three iron oxides (complexed iron, Fep; amorphous iron, Feo; free iron, Fed) in samples were determined to clarify the spatial distribution of iron and explore its impact factors. The mean contents of FeT, Fep, Feo and Fed were 28079.4, 152.0, 617.2 and 8285.3 mg⋅kg–1 of soil at 0–40 cm depth in the different sites, respectively. The means were significantly different across communities along the hydrological gradient, with the higher values for SA on the upper intertidal zone and for SPA on the lower intertidal zone, respectively. Iron and its forms were positively correlated with the total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen (TN) and clay, and negatively correlated with electrical conductivity (EC). The indexes of iron oxides (Fep/Fed, Feo/Fed and Fed/FeT) were also different across communities, with a higher value for SA, which were positively correlated with soil water content (WC) and TOC. The results indicate that a variety of plant community and soil property derived from the difference of hydrology might result in a spatial heterogeneity of iron in estuarine wetlands.