Bioavailability In Soil Research Articles

Reducing cadmium bioaccumulation in Theobroma cacao using biochar: basis for scaling-up to field

The intake of Cd-enriched food is the main Cd pathway for the nonsmoking population. In some cases, Cd bioaccumulates in edible plant parts which comprise risk to consumers, because of Cd is a harmful heavy metal that can cause potent environmental and health hazards. For instance, Cd enrichment of cacao seeds have led to Cd enrichment of cacao-based products. In Latin America and the Caribbean, Cd bioaccumulation in cacao seeds occurs in different regions with diverse edaphoclimatic conditions, which makes it difficult to select soil remediation alternatives. Limited resources require that potential amendments must be carefully investigated through laboratory and/or greenhouse conditions before scaling up to field experiments. In this study, we evaluated the effectiveness of four biochars: coffee-, quinoa-, and inoculated- and palm-biochar, derived from three feedstocks: coffee husk, quinoa straw, and oil palm residues, respectively. Biochars were applied in two rates (1 and 2% w/w) in two soils, one moderately acidic and one slightly alkaline (Cd-spiked and non-spiked). CCN-51 cacao plants were used for the greenhouse experiment. After 130 days, biometric parameters, the bioavailability of Cd in the soil, and the concentration of Cd and mineral nutrients in the plants were measured. Quinoa biochar at the 2% significantly decreased (P < 0.01), by ∼71%, bioavailable Cd in moderately acidic and slightly alkaline soils, and leaf-Cd by ∼48%. Soil pH, electrical conductivity, and effective cation exchange capacity were significantly (P < 0.01) correlated with bioavailable soil and leaf-Cd. Biochar characteristics, such as ash contents, basic cations content, and surface functional groups could be used as indicators for the selection of biochars to reduce Cd uptake by cacao. Additionally, application of quinoa derived biochar provided P and K, which could increase productivity to offset mitigation costs. Overall, incorporation of quinoa biochar at 2% rate is effective for lowering bioavailable Cd in different soil types which reduces leaf-Cd in cacao plants.

Double-edged effects of elevating temperature on the aging of exogenous arsenic in flooded paddy soils

Temperature variation can have a significant impact on arsenic (As) bioavailability in paddy soils. However, details regarding the transformation of exogenous As during the aging process in paddy soils at various temperatures remain unclear. This work investigated the effects of temperature on the As extractability and As species transformation of three paddy soils spiked with exogenous arsenate at 60 mg kg−1 under flooded aging and explored the related chemical and microbial mechanisms. The results showed that 0.05 M NH4H2PO4-extractable As decreased over time during flooded aging for 192 days, and it decreased by approximately one-third at 35 °C compared with 15 °C and 25 °C at the same aging time, indicating that higher temperatures facilitated the decrease in As extractability. As(V) reduction mainly occurred at 35 °C because the abundance and As(V)-reducing capacity of the predominant indigenous bacteria, the Bacillus sp strains, and the abundance of the arrA gene were significantly higher than those at 15 °C and 25 °C. The reduction of As(V) to As(III) and aging occurred simultaneously. The kinetic models were established, and the rate constants of the reduction and aging processes were obtained. Soil properties significantly affected the aging and reduction processes of extractable As(V). Our study indicated that elevating temperature had dual effects on the environmental risk of As in the flooded aging process. The previous definition of “aging” based on cationic metals needs to be updated according to the transformation characteristics of As species in flooded conditions. Our results addressed the necessity of impeding the reduction of As(V) in paddy soils under global warming.

Effect of wetting-drying cycles on the Cu bioavailability in the paddy soil amended with CuO nanoparticles

The extensive application of metal-based nanoparticles can pose environmental risks, but how the alternation of wet and dry caused by natural precipitation and artificial irrigation affects the environmental fate of nanoparticles is still unclear. Here, we investigated the underlying mechanisms of wetting-drying cycles (WDCs) on the Cu bioavailability in paddy soil treated with CuO nanoparticles (100 and 500 mg/kg) during 140 days by comparing with drought and flooding conditions. The results show that soil moisture content greatly affected the soil pH and redox potential. The bioavailable Cu contents in the WDCs exposed to CuO nanoparticles were positively correlated to moisture content and WDCs number. The fit result of the pseudo-second-order equation indicates that WDCs greatly prevented the aging process of Cu in soil. Furthermore, WDCs transformed oxidizable Cu to water-soluble, acid extractable and reducible Cu. WDCs markedly promoted the degradation of dissolved organic matter and the transformation of acid-soluble sulfate to water-soluble inorganic sulfate, meanwhile, significantly enhanced the contents of crystalline iron oxides by 22–57% and 82–326% with respect to drought and flooding, but reduced the level of ferrous iron by 37–67% compared to the flooding. µ-XRF analysis shows that the fate of CuO nanoparticles might be mainly determined by Fe under WDCs condition but by S in flooded soil. This study can provide a comprehensive assessment on the impact of natural precipitation and artificial irrigation on the environmental risks of MNPs.

Soil mineralogy-controlled phosphorus availability in soils mixed with phosphate fertilizer and biochar

The biochar amendment to soil proved to be beneficial to improve soil quality and provide nutrients. However, the effect of biochar on the availability of P are still controversial. We aim to study the effect of adding phosphate fertilizer and biochar on the P bioavailability in soils of different mineralogies. Eight biochars derived from biomass (rice husk and coffee husk), soil (sandy and clayey), and phosphate fertilizer (triple superphosphate) were produced. The biochar enrichment process with superphosphate was carried out before and after pyrolysis. Thus, we tested two biochar groups: 1) enriched biochars prior to pyrolysis; 2) enriched biochars after pyrolysis. These biochars were tested as P sources in soils of three mineralogies (kaolinite/oxide, kaolinite, and smectite). Batch sorption-desorption experiments were conducted. The sorbed P was fractionated to examine the factors controlling the retention of applied P. In the three soil mineralogies the use of enriched biochars prior to pyrolysis results in lower availability of P. In contrast, the enriched biochars after pyrolysis increase the bioavailability of P. The coffee husk biochar is more suitable than rice husk biochar to protect P from soil retention reactions. The use of sandy soil rather than clayey soil in enriched biochars compositions results in higher P content availability when applied to soils. The factor that controls the retention of P is the reaction between P, organic compounds, and Fe and Al compounds. The greater the relationship between biochar and soluble P in the fertilizer, the higher the increase of P retention.

Mechanisms of straw biochar’s improvement of phosphorus bioavailability in soda saline-alkali soil

Mechanisms of straw biochar’s improvement of phosphorus bioavailability in soda saline-alkali soil

Impact of Low Molecular Weight Organic Acids on Soil Phosphorus Release and Availability to Wheat

ABSTRACT Phosphorus (P) use efficiency (FPUE) is very low due to fixation of P with the hydrous oxides of iron and aluminum in acid soils and calcium in neutral to calcareous soil. The roots of wheat (Triticum aestivum) excrete low molecular weight organic acids (LMWOAs) to increase P bioavailability in P-deficient soil through acidification, chelation, and exchange mechanisms. However, the amount of LMWOAs excreted in the rhizosphere is small, and they undergo rapid microbial degradation. The present study was undertaken by applying different levels of LMWOAs and phosphorus to the soil followed by sowing of wheat seeds to learn the impact of applying LMWOAs, especially oxalic (OA) and citric acid (CA), on the yield and FPUE of wheat. The results showed that application of P fertilizer along with OA and CA significantly increased the Olsen P concentration in soil and in turn increased P uptake, FPUE, and yields of wheat. Application of OA @ 15 mg kg−1 recorded 20% (±0.22%) and 30% (±0.55%) higher grain and straw yield, respectively, over control and was more effective than CA. Among LMWOAs, application of OA @ 15 mg kg−1 was more effective than CA. Therefore, the application of OA has the potential to reduce the excess application of phosphorus and its buildup in soils and cause eutrophication of water bodies.

Effects of long-term mineral fertilization on silage maize monoculture yield, phosphorus uptake and its dynamic in soil

A long-term continuous silage maize ( Zea mays L . ) monoculture experiment (1993–2019) was conducted at Červený Újezd in the Czech Republic to assess the effects of different mineral fertilizers on phosphorus transformations and balance. An unfertilized control (C) was compared with i) ammonium sulfate (AS), ii) urea ammonium nitrate (UAN), iii) UAN + triple superphosphate and potassium chloride (UAN+PK), and iv) UAN + triple superphosphate and magnesium sulfate (UAN+PMg), respectively. The dry aboveground biomass yield (BY), P uptake by plants, bioavailable and stable soil P forms, soil P-sorption characteristics, as well as simple P-balance, sustainability yield index (SYI), and agronomic efficiency (AE) were evaluated. Maize P uptake, content, BY, AE, SYI, and P utilization over the 27 years increased in the order of UAN+PK > UAN+PMg > UAN > AS > C treatments. P uptake was positively correlated with bioavailable soil P and BY. AS and UAN only fertilizing caused a more negative P balance (on average −621 kg P ha –1 27 yrs –1 ) as compared to the control (–483 kg P ha –1 27 yrs –1 ). The bioavailable Al and Fe forms strongly influenced the soil P sorption parameters. As example, phosphorus sorption index increased to 137% for C, averagely to 183% for AS and UAN fertilizing treatments, and 124% for P fertilizing treatments in the year 2019 as compared to 1997 (=100%). Generally, almost all indices show that N only fertilizing (AS and UAN) significantly decreases the bioavailable and even the stable inorganic P forms and has a negative influence on P sorption parameters and thus, overall P-sustainability. The effect of this fertilizing system was even more negative than in the unfertilized control, due to the higher yield and P uptake in AS and UAN treatments. Although soil P was not a limiting nutrient for plant growth, it is possible to expect its direct influence on BY in AS and UAN treatments in the near future. • Although phosphorus was not limiting nutrient, P-sorption characteristics show low risk of P losses. • Unbalanced fertilizing with N, but without P, led to depletion of soil phosphorus, which was worse (–621 kg P ha –1 27 years –1 !) than at unfertilized control (–483 kg P ha –1 27 years –1 ). • Maize plants used even the stable inorganic P forms to maintain the biomass yield and phosphorus uptake. • Nitrogen appeared to be limiting nutrient in the experiment, which was one of the main reasons for yield decrease after 15 years after its establishment. • NPK fertilizing resulted in better sustainability index, P utilization as well as agronomic efficiency.

Enriching organic carbon bioavailability can mitigate soil acidification induced by nitrogen fertilization in croplands through microbial nitrogen immobilization

AbstractExcessive application of ammonium‐based N fertilizers promote nitrification, which is mainly responsible for intensive acidification in cropland soils. Thus, there is an urgent need for the development of control measures to manage soil acidification induced by N fertilization. In this study, we investigated the potential of enriching organic C bioavailability to mitigate acidification induced by N fertilization through microbial N immobilization using an indoor incubation experiment. Results showed that the sole application of ammonium sulfate [(NH4)2SO4] or urea to a cropland soil promoted nitrification of fertilizer N, and subsequently soil pH decreased by 0.48–1.00 units after 45‐d incubation. The combined application of glucose with N fertilizers induced microbial immobilization of almost all fertilizer N within 1 d and gradually induced mineralization of soil organic N after 1 wk of incubation. More than 65% of immobilized total extractable N was returned to soil solution and mainly existed as NH4+–N and extractable organic N, with the pH decrement being &lt;0.10 units after 45‐d incubation. These results indicated that (a) enriching organic C bioavailability in cropland soils intensified microbial N immobilization, (b) intensification of microbial N immobilization induced a buffering effect to regulate soil inorganic N supply, and (c) microbial N immobilization had great potential to inhibit soil acidification and retard aluminum mobilization. The results obtained in this study provide a theoretical strategy to control soil acidification and increase N use efficiency in croplands.

Organic anions facilitate the mobilization of soil organic phosphorus and its subsequent lability to phosphatases

PurposeOrganic anions commonly released from plant roots and microorganisms are widely reported to mobilize soil phosphorus (P). We characterized soil organic P that was mobilized by organic anions and assessed its amenability to hydrolysis by phosphatase enzymes.MethodsSix soils differing in organic P concentration were extracted with citrate, malate or oxalate solutions and incubated with preparations of phosphomonoesterase, phosphodiesterase, or phytase. Organic P compounds present in these extracts were putatively identified and quantified with solution 31P-NMR spectroscopy and the enzyme-labile P fractions were assessed by changes in molybdate-reactive P (MRP) concentration.ResultsOrganic P mobilization varied markedly among the organic anions. Extraction with 10 mM citrate was most effective and extracted 7.8-fold more total P than the water controls across all soils. Approximately 95% of the extracted P was non-MRP. The organic anions increased both the amount of P extracted and the proportion of the total extracted P that was phosphatase-labile. Phytase was generally the most effective enzyme with up to 60% of the total non-MRP being amenable to hydrolysis by phytase across all extracts. The presence of inositol hexakisphosphates in the extracts, as well as other forms of organic P including nucleic acids and phospholipids, was verified by 31P-NMR with concentrations dependent on both organic anions and soil type.ConclusionThe combination of organic anions and phosphatases represents a key mechanism by which plants and microorganisms can enhance the bioavailability of soil P. This has important implications for understanding P dynamics in natural and managed ecosystems and for ongoing efforts to improve the P-acquisition efficiency of agricultural plants.

Mobility, bioaccessibility, pollution assessment and risk characterization of potentially toxic metals in the urban soil of Lahore, Pakistan.

The present study is based on the measurement of potentially toxic metal contents employing various extraction methodologies aimed at the evaluation of their mobility, bioaccessibility and bioavailability in the urban soil (n = 56) of Lahore, Pakistan. Selected metal levels in the soil were quantified using flame atomic absorption spectrometry. On the average basis, aqua regia and glycine extracts revealed comparatively higher contents for most of the metals; average concentrations of Fe, Mn, Zn, Pb, Cu, Cr, Co and Cd were found at 1566, 451.1, 114.8, 52.84, 39.15, 24.82, 12.59 and 3.953mg/kg in aqua regia extract, while in glycine extract the metal levels were found at 579.6, 174.2, 74.72, 49.74, 19.28, 7.103, 4.692 and 3.357mg/kg, respectively. However, Cd, Pb, Cu and Zn showed significantly higher mobility and bioavailability in the soil, while Co, Fe and Mn were least mobile/bioavailable. The pollution index was assessed in terms of enrichment factor and modified degree of contamination which revealed severe to significant contamination and anthropogenic enrichment of Cd, Pb, Cu and Zn. Multivariate analysis showed mostly anthropogenic contributions for Zn-Cu-Cr-Pb-Cd. Health risk assessment revealed relatively higher exposure of the metals through ingestion, while only minor contributions were noted for inhalation and dermal contact. Hazard quotient index was within the safe limit (< 1.0) in all soil extractions, thereby indicating no significant non-carcinogenic health risks. The incremental lifetime cancer risk for Cr (4.1E-06) through ingestion was comparatively higher than the safe limit which showed significant lifetime cancer risk to the local population.

Cadmium and lead transfer factors to kale plants (Brassica oleracea var. acephala) grown in mountain agroecosystem and its risk to human health.

The aim of the present study is to assess soil Cd and Pb contamination in kale (Brassica oleracea var. acephala) production sites in mountain agroecosystem, as well as its potential risk to human health. The study was carried out within 24 kale-production sites located in mountainous region of Rio de Janeiro (Brazil). Soil, plant, and fertilizer samples were collected in all assessed properties. Pseudo-total and bioavailable soil Cd and Pb content and their concentration and amount accumulated in plants were analyzed. The recorded results were used to calculate the pollution index. Risks to human health associated with kale consumption were assessed by comparing the limits set by the Brazilian regulating agency and by calculating estimated daily intake (EDI), noncarcinogenic target hazard quotient (THQ), and carcinogenic risk factor (CRF). Soil Cd and Pb enrichment was observed. Inappropriate management adopted in the assessed sites and terrain slope and the intensive use of mineral (phosphate and potassium) and organic (poultry litter) fertilizers were the main factors contributing to increase soil Cd and Pb pseudo-total and bioavailability contents. Most Cd and Pb contents in leaves, in natura, exceed the maximum values set by the Brazilian regulating agency. The present EDI, THQ, and CRF results recorded for these metals were within the tolerable ranges.

Influence of Dietary Lipid Type on the Bioavailability of DDT and Its Metabolites in Soil: Mechanisms and Health Implications

The impact of dietary lipid type on DDTr (DDT and its metabolites) relative bioavailability (RBA) in soil was investigated using an in vivo mouse model and in vitro assays. Three different lipids were long chain triglycerides (LCT), medium chain triglycerides (MCT), and short chain triglycerides (SCT). DDTr-RBA markedly (p < 0.05) increased from 51.3 ± 10.8% (control) to 94.6 ± 15.9% (10% w/w LCT) and 112 ± 20.8% (20% LCT) in LCT amended treatments. A significant increase in DDTr-RBA (92.2 ± 9.84%, p < 0.05) was also observed when mice were administered diets containing 20% MCT; however, no influence on DDTr-RBA was observed for SCT amended diets. Mechanism exploration showed that LCT and MCT enhanced DDTr solubilization by a factor of 7.31-9.59 compared to controls as a consequence of micelle formation which promoted DDTr mobilization from soil. LCT significantly enhanced DDTr intestinal absorption via increasing synthesis and secretion of apolipoprotein B 48 (32.2 ± 2.08 mg/L), compared to MCT (22.1 ± 1.32 mg/L) and SCT (15.5 ± 2.03 mg/L) treated Caco-2 cells. Mouse gut microflora analysis highlighted that LCT and MCT may increase intestinal permeability by regulating abundance of Lactobacillus, which may influence the absorption of DDTr.

Determination of elemental bioavailability in soils and sediments by microwave induced plasma optical emission spectrometry (MIP-OES): Matrix effects and calibration strategies.

In the past few years, microwave induced plasma optical emission spectrometry (MIP-OES) has generated great interest as an alternative technique to inductively coupled plasma-based techniques due to its lower operational cost. Since MIP-OES suffers from severe matrix effects due to easily ionizable elements (EIEs) (Na, Ca, etc.), it is unclear whether this technique could be employed for elemental bioavailability studies in soils and sediments since the main extractant solutions employed in such works may contain high levels of these elements. Thus, the aim of this work was to evaluate the feasibility of MIP-OES as a detector for such applications. To this end, the influence of different extractant solutions (0.25molL-1 MgCl2, 0.25molL-1 CaCl2, 0.10molL-1 acetic acid, 0.05molL-1 Na2EDTA, 0.25molL-1 NaNO3, 0.25molL-1 NaOAc/HOAc and 0.10molL-1NH2OH·HCl) on the analyte emission of several elements (As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Rh, Se, Sr and Zn) was investigated. Results were compared to those obtained using a reference solution made of 5% w w-1 HNO3 solution. For saline extractant solutions, both the optimum nebulizer gas flow rate (Qg) and analyte emission were modified with regard to the reference solution. In general, the optimum Qg was reduced by between 0.1 and 0.2Lmin-1 for both ionic and atomic lines. Under optimum Qg conditions, analyte emission was supressed by saline solutions except for atomic lines with an upper electronic state below 4eV, which were enhanced. The magnitude of matrix effects was strongly dependent on EIE ionization energy. The lower the ionization energy, the greater the matrix effects were registered. No measurable matrix effects were registered on both Qg and analyte emission within experimental uncertainties for NH2OH·HCl and acetic acid extractant solutions. Experimental data suggest that matrix effects were related to changes in plasma characteristics and the analyte excitation/ionization mechanism. To mitigate matrix effects and improve long-term MIP-OES performance, internal standardization using either Rh (343.489nm and 369.236nm) or OH molecular emission band (308.958nm) was required. This calibration methodology was successfully applied to the study of the elemental bioavailability in soil samples from a vineyard affected by copper-based fungicides and sediment samples from an area affected by mining waste.

Selenium uptake and accumulation in winter wheat as affected by level of phosphate application and arbuscular mycorrhizal fungi

Selenium (Se) is an advantageous element to crops. However, the influence of arbuscular mycorrhizal fungi (AMF), phosphate (P) and selenite in soil on Se uptake by winter wheat remain elusive. Pot trials were carried out including seven levels of P (0, 12.5, 25, 50, 100, 200 or 400 mg kg−1) and non-mycorrhizal inoculation (NM), inoculation of Funneliformis mosseae (F.m) or Glomus versiforme (G.v). The present results found that grain phosphorus concentration increased with increase of P level from 0 to 100 mg kg−1 and then tended to plateau, while grain Se concentration decreased with the level of P from 0 to 400 mg kg−1. Based on mathematical modeling, inoculation of F.m or G.v dramatically improved grain Se concentration by 16.90% or 12.53% under the lower level of P (48.76 mg kg−1). Furthermore, partial least squares path modeling (PLS-PM) identified that both up-regulated of the expression of AMF-inducible phosphate transporter and improved Se bioavailability in rhizosphere soil contributed to enhancing plant Se concentration under P levels ≤ 100 mg kg−1. The present study demonstrated that AMF combined with 48.76 mg kg−1 P applied in soil can not only achieve high grain yield, but also fully exploit the biological potential of Se uptake in wheat.

Assessment of the Bioavailability of Mercury Sulfides in Paddy Soils Using Sodium Thiosulfate Extraction - Results from Microcosm Experiments

Mercury sulfides (HgS), one of the largest Hg sinks in the lithosphere, has long been considered to be highly inert. Recently, several HgS speciation (e.g., nano- or micro-sized HgS particles) in paddy soils have been found to be reactive and bioavailable, increasing the possibility of methylation and bioaccumulation and posing a potential risk to humans. However, a simple and uniform method for investigating HgS bioavailability is still lacking. To address this issue, we extracted dissolved Hg from HgS particles by sodium thiosulfate (Na2S2O3) in paddy soils and analyzed the correlation between extracted Hg and soil methylmercury (MeHg). Results showed that the amounts of Hg extracted by Na2S2O3 had a strong positive correlation with the levels of soil MeHg (R 2 adj = 0.893, p < 0.05). It is suggested that Na2S2O3 extraction may be a good method of predicting Hg bioavailability in paddy soils. Our results would help to give clues in better predicting Hg risk in natural environments.

The performance and mechanism of cadmium availability mitigation by biochars differ among soils with different pH: Hints for the reasonable choice of passivators

The performances of passivation materials mitigating Cadmium (Cd) bioavailability considerably vary with the pH condition of Cd-contaminated soils. However, less information was available for the method of improving Cd passivation efficiency taking into account the pH of the targeted soil. Furthermore, the underlying mechanism of Cd availability mitigation in soils with different pH has not been clearly explored. In this study, cotton straw biochar (CSB) and its modified products using NaOH (CSB–NaOH) were prepared and applied in two kinds of Cd-contaminated soils with different pH. It was found that CSB-NaOH was more effective than CSB in regulating the Cd bioavailability in the acid soil, while the opposite tendency was observed in alkaline soil. The difference of the Cd passivation efficiency is correlated with contributions of various Cd-biochar binding mechanisms, which cation exchange mechanism is largely eliminated for CSB-NaOH. The interaction of Cd with CSB/CSB-NaOH was further evidenced through characterization results of Scan Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and X-ray Photoelectron spectroscopy (XPS). Characterization results proved that carboxyl, hydroxyl and ethyl groups were the key functional groups involved in Cd passivation. XPS results showed that Cd binding methods varied between CSB and CSB-NaOH, which Cd2+ and Cd–O were the main form of Cd binding to CSB while Cd–O was the main form on CSB-NaOH. In this work, it was demonstrated that in acid soil, pH change caused by biochar plays a more significant role in controlling the Cd bioavailability, while in alkaline soil, the strength of the Cd-biochar interaction is more decisive for the Cd passivation efficiency. This work provides information on how to select the suitable passivator to decrease the Cd bioavailability in terms of different soil pH and property.

Effects of spatial expansion between Phragmites australis and Cyperus malaccensis on temporal variations and bioaccumulation of vanadium in coastal marshes of the Min River estuary, Southeast China

Vanadium (V) plays an important role in physio-ecological processes of marsh plants. The effects of spatial expansion between invasive species (Phragmites australis, PA) and native species (Cyperus malaccensis, CM) on temporal variations and bioaccumulation of V in coastal marshes of the Min River estuary were investigated by space-for-time substitution method. In situ filed sampling was conducted in PA marsh (PAM, before expansion), CM marsh (CMM, before expansion) and ecotonal marsh (EM, during expansion, marsh plants were denoted by PA' and CM') in different seasons. Results showed that, over all sampling seasons, the mean V contents in marsh soils ranged from 99.71 to 108.41 mg·kg−1 which exceeded its background value in soils of Fujian province (78.3 mg·kg−1). The V levels in soils differed among seasons or marshes and higher values in PAM, EM and CMM soils were generally observed in spring and winter. The temporal variation of V levels in EM soil rested with the alterations of pH, SOM and plant ecological traits during spatial expansion. The V contents in PA, PA', CM' and CM differed among tissues and higher bioaccumulation occurred in roots. The V levels in tissues differed among species or seasons, which could be ascribed to the differences in ecological traits among plants and the competitive absorption for V by plants during spatial expansion. This paper confirmed that the V in marsh soils of the Min River estuary existed enrichment process and the spatial expansion between PA and CM promoted its enrichment in soils and its bioaccumulation by plants. The findings of this study were favorable for understanding the biogeochemical behaviors of V in marsh ecosystem and strengthening the marsh conservation by regulating its bioavailability in soils.

Toward a Global Model for Soil Inorganic Phosphorus Dynamics: Dependence of Exchange Kinetics and Soil Bioavailability on Soil Physicochemical Properties.

The representation of phosphorus (P) cycling in global land models remains quite simplistic, particularly on soil inorganic phosphorus. For example, sorption and desorption remain unresolved and their dependence on soil physical and chemical properties is ignored. Empirical parameter values are usually based on expert knowledge or data from few sites with debatable global representativeness in most global land models. To overcome these issues, we compiled from data of inorganic soil P fractions and calculated the fraction of added P remaining in soil solution over time of 147 soil samples to optimize three parameters in a model of soil inorganic P dynamics. The calibrated model performed well (r 2 > 0.7 for 122 soil samples). Model parameters vary by several orders of magnitude, and correlate with soil P fractions of different inorganic pools, soil organic carbon and oxalate extractable metal oxide concentrations among the soil samples. The modeled bioavailability of soil P depends on, not only, the desorption rates of labile and sorbed pool, inorganic phosphorus fractions, the slope of P sorbed against solution P concentration, but also on the ability of biological uptake to deplete solution P concentration and the time scale. The model together with the empirical relationships of model parameters on soil properties can be used to quantify bioavailability of soil inorganic P on various timescale especially when coupled within global land models.

Gypsum application lowers cadmium uptake in cacao in soils with high cation exchange capacity only: A soil chemical analysis

AbstractSoil liming to lower cadmium (Cd) bioavailability is challenged in perennial cacao orchards by the low penetration of lime in soils, not reaching deeper roots. Some studies suggest that gypsum (CaSO4) could reduce Cd uptake by enhanced Ca2+:Cd2+ competition at the root surface. A pot experiment was conducted to identify soil conditions affecting gypsum efficacy in cacao plantlets (5‐month‐old CCN‐51). Plants grew for 115 days in soils sampled from six locations with variable cation exchange capacity (CEC, 6–50 cmolc.kg−1) and soil solution Ca2+ (1.3–17 mM). Soils were either mixed or not mixed with a dose equivalent to 4.0 Mg gypsum ha−1. Leaf Cd concentration in plants grown on gypsum applied soils was statistically lower compared to unamended soils in only one of the six soils. The reduction factor of leaf Cd concentrations due to gypsum (RF = control/amended Cd concentration ratio) ranged from 2.32 (high effect) to 0.76 (no effect), and it was positively correlated with the Ca2+ in the solution of the unamended soil (R2 = 0.58) and with increasing CEC (R2 = 0.52), that is, gypsum only reduced Cd bioavailability in high CEC soils, confirming a trend found in earlier publications. Soil solution analyses showed that gypsum application enhanced total dissolved Cd by forming CdSO40 complexes with, in some cases, even enhanced Cd2+ ion activities, likely related to Ca2+‐induced Cd2+ mobilisation. Data suggest that Ca2+ derived from gypsum has counteracting effects on Cd mobilisation and ion competition at the root surface. The former reactions are less pronounced in high CEC soils. More research is needed to unravel gypsum effects on high Ca2+ soils to corroborate our findings.Highlights The effect of soil properties on the efficacy of gypsum to reduce Cd uptake in cacao was studied. Gypsum only reduced Cd uptake in cacao in the soil sample with highest CEC and highest Ca in solution. This finding implies a possible competition between Ca2+ and Cd2+ for root uptake in cacao.

Arsenic fractionation and mobilization in agricultural soils of NE Punjab, India

Bioavailability of arsenic (As) is strongly controlled by its partitioning in different soil constituents which alternatively determines its toxicity extent even though total As contents of soils might be comparable. Five soil samples with contrasting crop practices and physico-chemical nature were examined for As contents in different constituents by sequential extraction process and its mobility under oxic and anoxic conditions in presence of competing anions. Soils are of alkaline nature (pH 8.2–8.7) with high carbon content (C/N = 10.3–11.9). Mobilization of As increases with time and enhanced by presence of competitive anions (NO3− + PO43-) with a greater mobility under anoxic condition compared to that in oxic condition reaching up to ∼19% of soil As. Overall decrease in pH was observed that was better pronounced under oxic conditions and drop in pH was relatively more in NO3− + PO43- containing reactors. Fluoride, Cl− and SO42- release were negligible within 21 days where lesser SO42- was measured in anoxic condition contrary to F− and Cl−. Almost complete NO3− and PO43- retention under anoxic reactors together with greater As release imply an ion exchange mechanism of As mobilization. Poor bioavailability of soil As was envisaged because of negligible water exchangeable As contents. However, a ligand exchange mechanism is proposed between PO43- and HAsO42- resulting greatest As extraction through phosphate extraction process where significant As contents remained intact onto the crystalline phases.