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The oxidation of ammonia to nitrite, which constitutes the initial and rate-limiting step in the nitrification process, plays a pivotal role in the transformation of ammonia within soil ecosystems. Due to its susceptibility to a range of pollutants, such as heavy metals, pesticides, and pharmaceuticals, nitrification serves as a valuable indicator in the risk assessment of chemical contaminants in soil environments. Here, we analyzed the effects of cadmium (Cd) treatment on soil potential nitrification rate (PNR), and the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities. The results showed that, under 1 day incubation, the soil PNR with Cd 0.5 mg kg -1 was a little higher but not statistically significant than that with zero mg kg -1 . Then, the soil PNR increased with the increasing Cd concentration from 0.5 to one mg kg -1 , and continuously declined from 1 to 10 mg kg -1 . Moreover, we predicted the bacterial functions of samples with hormetic Cd dose (one mg kg -1 ) by PICURSt (Phylogenetic Investigation of Communities Reconstruction of Unobserved States), and found that the expression of protein disulfide isomerase (PDI) increased with the hormetic Cd dose. PDI is known to enhance the activity of compounds containing -SH or -S-S which can help prevent oxidative damage to membranes. The soil PNR was significantly correlated with AOA abundance rather than AOB, even the abundance of AOB was higher than that of AOA, indicating that AOA functionally predominated over AOB. Our study effectively evaluated the Cd toxicity on soil microbial community and clearly illustrated the ecological niches of AOA and AOB in the agricultural soil system studied, which will be instructive for the sustainable development of agriculture., Competing Interests: The authors declare there are no competing interests., (©2025 He et al.)

The phosphate-modified biochar (BC) immobilizes cadmium (Cd), yet little is known about how phosphate species affect Cd detoxification in contaminated soils. We developed phosphate-modified biochar through the pyrolysis of wheat straw impregnated with three types of phosphate: mono‑potassium phosphate (MKP), dipotassium hydrogen phosphate (DKP), and tripotassium phosphate (TKP). The Cd adsorption mechanism of modified biochar was investigated by biochar characterization, adsorption performance evaluation, and soil incubation tests. The results demonstrated that the efficiency of biochar in immobilizing Cd 2+ followed the order: TKP-BC > DKP-BC > MKP-BC. The TKP-BC had the highest orthophosphate content, the fastest adsorption rate, and the largest adsorption capacity (Langmuir) of 257.28 mg/g, which is 6.31 times higher than that of the unmodified BC (CK). In contrast, pyrophosphate was predominant in MKP-BC and DKP-BC. The primary adsorption mechanism for Cd 2+ was precipitation, followed by cation exchange, as evidenced by the formation of CdP minerals on the BC surface, and an increase of K + in solution (compared to water-soluble K + ) and a decrease of K + in the biochar during adsorption. Desorption of Cd from the TKP-BC after adsorption was 9.77 %-12.39 % at a pH of 5-9, much lower than that of CK. The soil incubation test showed the diethylenetriaminepentaacetic acid extracted Cd of TKP-BC, MKP-BC, and DKP-BC was reduced by 67.93 %, 18.41 % and 31.30 % over CK, respectively. Using the planar optodes technique, we also found that TKP-BC had the longest effect enhancing in situ soil pH. This study provides a theoretical basis for developing heavy metal pollution control technology using green remediation materials and offers insights into the remediation mechanisms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Microorganisms can modulate the contents of cadmium (Cd) and zinc (Zn) in wheat grains. Increasing the essential nutrient element Zn and decreasing the toxic element Cd in wheat grains can significantly improve human health. To characterize the specific bacterial communities associated with Cd and Zn accumulation in wheat, we conducted a field experiment by planting wheat cultivars differing in their capacity for Cd and Zn accumulation. The grain Cd contents in wheat cultivars YN23 (0.078 mg kg -1 ), JN17 (0.080 mg kg -1 ), YN836 (0.081 mg kg -1 ) and LM2 (0.091 mg kg -1 ) were significantly lower than those in ZM32 (0.16 mg kg -1 ). The Zn contents were significantly higher in the grains of JN17 (44.36 mg kg -1 ), LM2 (42.22 mg kg -1 ) and ZM32 (43.19 mg kg -1 ) than YN23 (27.05 mg kg -1 ) and YN836 (29.70 mg kg -1 ). On the basis of contents and bio-concentration factors of Cd and Zn in wheat grain, JN17 and LM2 were identified as low-Cd- and high-Zn-accumulating cultivars, YN23 and YN836 were low-Cd- and low-Zn-accumulating cultivars, and ZM23 was a high-Cd- and high-Zn-accumulating cultivar. The relative abundance values of Gemmatimonadaceae, Sphingomonadaceae and Beijerinckiaceae in the rhizospheres of low-Cd cultivars were significantly higher than those of high-Cd cultivars. High-Zn cultivars had higher abundance of Rhodanobacteraceae in the rhizosphere than did low-Zn cultivars. The low-Cd- and high-Zn-accumulating cultivars were enriched in Alphaproteobacteria and Gemmatimonadaceae, and strengthened nitrification function including aerobic_ammonia_oxidation and aerobic_nitrite_oxidation in the rhizosphere soil, thus contributing to the decreased Cd and increased Zn contents in wheat grains. Microbial technology is a promising method to control the contents of Cd and Zn in wheat grains., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Heavy metal-contaminated farmland, especially for cadmium (Cd), is being used for agricultural production in large scale due to the increasing food demand. Thus, minimizing the influx of Cd to the human food chain is urgently needed. Screening for stably low Cd and moderately high micronutrient wheat cultivars is one of the most feasible and effective approaches to ensure food safety and quality. Here, the Cd accumulation by 72 wheat cultivars was identified in field 1, and the stability of Cd accumulation in these cultivars was tested in fields 2 and 3. The effects of Cd on micronutrient (zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), and boron (B)) uptake in grains were also investigated. Nine of the 24 low-Cd wheat cultivars identified by screening showed stably low-Cd and moderately high micronutrient concentrations in grain. Nine cultivars exhibited unstable low-Cd accumulation characteristics, and another five cultivars contained significantly lower Zn concentrations in grain in at least two experimental fields. One low-Cd cultivar also had low Zn, Cu and Mn concentrations in grain. The accumulation of Cd in wheat grain had little effects on the uptake of Fe. Grain Cd concentration correlated positively with the dry weight of stem and root, and negatively with the spike length. There was no correlation between grain Cd concentration and wheat yield. The selected cultivars with stably low-Cd accumulation and moderately high micronutrient concentrations in grain are recommended for cultivation in slightly to moderately Cd-contaminated farmland to ensure food safety for the growing human population., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Low-cadmium (Cd) accumulating wheat cultivars (LAWC-Cds) can effectively reduce the total Cd content in wheat grains (Grain-Cd). Thirteen LAWC-Cds were planted in three fields to study the enrichment, transport, and accumulation patterns of Cd in LAWC-Cds. Compared with the soil properties before planting, the soil pH and the total Cd content in the soil decreased, while the Cd content in the diethylenetriaminepentaacetic acid extract, soil conductivity, and soil organic matter increased at wheat maturity. The Cd enrichment capacity of the different organs of wheat decreased in the following order: root > leaf > rachis > stem > glume > grain. The dynamics of Cd accumulation in roots affected Grain-Cd, and these factors were negatively correlated. The Cd content and Cd accumulation in all organs of LAWC-Cds showed strong negative correlations with the lengths of the first and second internodes and highly significant positive correlations with both grains per spike and awn length. Structural equation modeling showed that the Cd content of wheat organs had the most direct effect (0.639) in determining Grain-Cd, and soil properties had the largest effect (0.744) in influencing Grain-Cd. This study is important for screening wheat cultivars with stable low Cd-accumulation characteristics. [ABSTRACT FROM AUTHOR]

Humic acid amendments in the remediation of soils contaminated with heavy metals have received widespread attention. However, the impacts and related mechanisms of mineral-based humate substances on the remediation of alkaline paddy soils with different levels of cadmium (Cd) contamination are still unclear. Pot trials with four mineral-based potassium humate (MBPH) doses (0, 0.25%, 0.5%, 1%, w/w) and three Cd rates (slightly, moderately, and highly, 1, 2, and 4 mg Cd kg−1) were conducted to evaluate the effects of MBPH on rice. Results showed that the application of MBPH effectively reduced brown rice Cd concentrations of all Cd rates by 46.82–65.04%, 44.02–59.21%, and 15.84–43.99%, such that Cd in brown rice fell within the safe edible standards in the highly contaminated soils with the 0.5% and 1% MBPH applications. The application of MBPH significantly alleviated Cd toxicity by increasing soil solution pH, dissolved organic carbon (DOC), and potassium (K) and decreasing free Cd and the bioavailability of rhizosphere soil Cd, as reflected by promoting rice plant growth, photosynthesis, Fv/Fm, and antioxidant enzymes activities. Additionally, high dose applications (0.5% and 1%) of MBPH significantly reduced the translocation factor of Cd from flag leaf to brown rice. Furthermore, the application of MBPH enhanced the accumulation of mineral elements (iron, manganese, copper, zinc, potassium) in brown rice. Stepwise regression analysis revealed that soil solution K at maturity stage and soil solution DOC at tillering and filling stages were the most important factors affecting Cd accumulation in brown rice under slightly, moderately, and highly Cd-contaminated soils, respectively. Therefore, MBPH application on slightly and moderately Cd-contaminated alkaline soils contributed to achieving rice grains rich with mineral elements but Cd free and Cd safe in highly Cd-contaminated soil. [ABSTRACT FROM AUTHOR]

Toxic metal-contaminated farmland from Cadmium (Cd) can enhance the accumulation of Cd and impair the absorption of mineral elements in brown rice. Although several studies have been conducted on Cd exposure on rice, little has been reported on the relationship between Cd and mineral elements in brown rice and the regulatory mechanism of rhizosphere microorganisms during element uptake. Thus, a field study was undertaken to screen japonica rice cultivars with low Cd and high mineral elements levels, analyze the quantitative relationship between Cd and seven mineral elements, and investigate the cultivar-specific response of rice rhizosphere bacterial communities to differences in Cd and mineral uptake in japonica rice. Results showed that Huaidao-9 and Xudao-7 had low Cd absorption and high amounts of mineral nutrient elements (Fe, Zn, Mg, and Ca, LCHM group), whereas Zhongdao-1 and Xinkedao-31 showed opposite accumulation characteristics (HCLM group). Stepwise regression analysis showed that zinc, iron, and potassium are the key minerals that affect Cd accumulation in japonica rice and zinc was the most important factor, accounting for 68.99 %. The accumulation of Cd and mineral elements is potentially associated with rhizosphere soil bacteria. Taxa enriched in the LCHM rhizosphere (phyla Acidobacteriota and MBNT15) indicated the high nutrient characteristics of the soil and reduced activity of Cd in soil. The HCLM rhizosphere was highly colonized by metal-activating bacteria (Actinobacteria), lignin-degrading bacteria (Actinobacteria and Chlorofexi), and bacteria scavenging nutrients and trace elements (Anaerolinea and Ketobacter). Moreover, the differences in the uptake of Cd and mineral elements affected predicted functions of microbial communities, including sulfur oxidation and sulfur derivative formation, human or plant pathogen, and functions related to the iron oxidation and nitrate reduction. The results indicate a potential association of Cd and mineral elements uptake and accumulation with rhizosphere bacteria in rice, thus providing theoretical basis and a new perspective on the maintenance of rice security and high quality simultaneously. [Display omitted] • Low-Cd and high mineral element cultivar rhizosphere were highly colonized by Acidobacteriota and sulfate-reducing bacteria. • High-Cd and low mineral element cultivar rhizosphere were highly colonized by lignin-degrading and nutrient removal bacteria. • Differences in the uptake of Cd and mineral element affected microbial community functions predicted by FAProTax. [ABSTRACT FROM AUTHOR]

Phytoextraction is an effective technique for removing cadmium (Cd) from contaminated farmland, thus achieving real ecological restoration. To clarify the potential of peanut phytoextraction, we designed a pot experiment to assess the Cd accumulation in peanut. In addition, the contribution of rhizosphere microorganisms in Cd accumulation was explored. The results demonstrate that the Cd content in peanut tissue ranked as follows: stem > leaf > root > needle > husk > kernel, with Cd mainly accumulated in the stems (41.92%) and leaves (40.27%). The bioconcentration factor for all cultivars was greater than 1, in agreement with the concept of phytoextraction. Cd extraction from peanut plants grown per season was appreciable, estimated as being from 28.5 g Cd ha−1 to 121.5 g Cd ha−1. Subsequently, based on the Cd accumulation characteristics, cultivars BS1016 and HY20 were identified as the high Cd-accumulating cultivars (HACs), and LH11 and LH14 were identified as the low Cd-accumulating cultivars (LACs), for further study as specific cultivars. For Cd-contaminated soil, high accumulation in HACs was associated with increased Cd bioavailability. The peanut rhizosphere attracted different microorganisms to cope with Cd stress. Compared with LACs, the rhizosphere of HACs tended to be enriched with high Cd-resistant microorganisms, which directly or indirectly participate in Cd activation (for example, Acidimicrobiia class of bacteria, Rhizophlyctis genus of fungi). Correlation analysis confirmed that Rhizophlyctis was a good choice to enhance the potential for Cd phytoextraction using peanut. This study demonstrates the advantages and rhizosphere mechanisms of using peanut for bioremediating Cd-contaminated soil, providing a new approach for remediation and targeted regulation of Cd-contaminated farmland. [Display omitted] • The bioconcentration factor of Cd in all peanut tissues was greater than 1. • Peanut has considerable ability to bioaccumulate Cd in aboveground tissues. • High-cadmium peanut cultivars mobilize Cd mainly through soil acidification. • Cultivars and Cd treatments create specific microbial communities in the peanut rhizosphere. • Rhizophlyctis is the most recommended fungus for improving phytoextraction potential. [ABSTRACT FROM AUTHOR]

Abstract Accumulation of pollutants, especially heavy metals in river delta systems, pose a severe threat to the ecological environment and also hinder sustainable development of deltas. A total of 390 samples were collected from farmlands throughout the Yellow River Delta (YRD), the fastest growing delta in the world, to explore the holistic distribution characteristics and restrictive environmental factors of mercury (Hg), cadmium (Cd), arsenic (As), lead (Pb), and chromium (Cr) in the soil. Results indicated that soils in farmlands at the YRD had relatively low average concentrations of selected elements with non-contamination level. This is due to low elemental contents of loess parent materials and less human activities. These elements in soils had distinct spatial distributions and disparities from different categories, which were predominately determined by soil physicochemical properties such as cation exchange capacity, organic matter content, clay fraction and soil acidity. Sodium salt played a vital role in this delta for soil salinization. Agricultural inputs, industrial emissions, and river suspended sediments were the three primary sources of these elements. Of these elements, 65% of Hg came from atmospheric deposition, 66% of Cd was sourced from industrial emissions, 53% of As and 46% of Pb originated from agricultural inputs, and 64% of Cr was rooted from parent materials. Based on these findings, critical strategies including controlling the agrochemical input and removing industrial pollutant emission were proposed for sustainable development of the YRD. Graphical abstract Image 1 Highlights • CEC, SOM, clay fraction and soil acidity determined elemental distributions. • Sodium salt played a vital role for soil salinization. • Agricultural, industrial sources, and river sediments were primary origins. • Attentions should be paid to the increasing potential pollution risk of Cd and As. [ABSTRACT FROM AUTHOR]

Cadmium pollution in farmland has become a potential threat to human health. Planting low-cadmium accumulation cultivars (LACs) is an effective green technology to ensure food safety. Previous studies mainly focused on the cadmium content, while ignoring the cadmium resistance. In this study, a pot experiment was designed to analyze the cadmium accumulation and resistance characteristics of 30 peanut cultivars in different cadmium-treated soils. Five single evaluation methods were performed to evaluate cadmium resistance, and the differences in their evaluation results were resolved by the fuzzy Borda method. As a result, a combinatorial evaluation model for cadmium resistance was successfully established. The cluster analysis of the kernel cadmium content screened LH11, LH14, YH9414, SNH26, WH8, SLG and FH1 as potential cultivars with stably low-cadmium accumulation. The kernel cadmium content of these cultivars decreased by 24.76 % to 43.12 % under 0.5 mg Cd kg−1 soil (T1) and 30.45 % to 47.48 % under 1 mg Cd kg−1 soil (T2) compared with HY25. Ultimately, LH11 was the recommend cultivar, which had the advantage of high resistance on the basis of low cadmium. This study identified valuable cultivars for safe utilization of soil and safeguarding human health, and provided new ideas for comprehensive screening of cultivars suitable for contaminated fields. [Display omitted] • Seven cultivars had lower Cd content in kernels by 24.76 %–47.48 % than the high Cd cultivar. • A combinatorial evaluation model for crop resistance to Cd was constructed by fuzzy Borda method. • The cultivar screening procedure considered Cd resistance on the basis of low Cd. • The cultivar LH11 was the excellent candidate for the safe utilization of polluted farmland. [ABSTRACT FROM AUTHOR]

Wheat cultivars with low cadmium (Cd) accumulation (WCCA-Cd) are widely used on Cd-contaminated farmland and can effectively reduce the grains Cd content to achieve the clean production in agriculture. However, there is a lack of soil Cd content thresholds specifically for the WCCA-Cd. To achieve safer production of wheat grains, a prediction model for WCCA-Cd was developed based on total Cd content in wheat grains (Grain-Cd) and soil factors using 379 soil‒wheat datasets from 10 field experiments in this research. The adaptability of the prediction model was tested using 312 pairs of data. Descriptive statistics (N = 379) showed that soil pH ranged from 4.28 to 8.76, the total Cd content in soil (Soil-Cd) ranged from 0.09 to 10.25 mg kg−1, and Grain-Cd ranged from 0.002 to 1.35 mg kg−1. Correlation analysis showed that Grain-Cd had a highly significant negative correlation with soil organic matter (SOM), soil pH, and soil conductivity (EC) and a highly significant positive correlation with Soil-Cd and Cd content in the diethylenetriaminepentaacetic acid extraction state (DTPA-Cd) (P < 0.001). The bioconcentration factor (BCF) decreased with increaseing soil pH. Both random forest and stepwise regression equations indicated that the most important factors affecting Cd bioeffectiveness were Soil-Cd and soil pH, explaining 80% of the variation in Grain-Cd. The prediction model indicated a soil Cd threshold (0.23–1.25 mg kg−1) for the safe production of WCCA-Cd at soil pH (4–9), which has a wider range of applicability compared with the Chinese Soil Safety Standards. Therefore, these results can quantify the grain Cd content of WCCA-Cd and guide the safe and clean production of WCCA-Cd on different Cd contaminated farmlands. [Display omitted] • Grain Cd content prediction was based on 13 low-Cd wheat cultivars from field experiments. • The Cd bioconcentration factor of wheat grains decreased with increasing soil pH (pH > 5.5). • Soil Cd content and pH were the main soil factors affecting Cd accumulation in wheat grains. • Soil Cd thresholds were derived for the safe production of low-Cd-tested wheat cultivars. [ABSTRACT FROM AUTHOR]

Planting wheat cultivars with low cadmium (Cd) accumulation could help overcome grain Cd contamination. However, the variation in low-Cd accumulation characteristics as influenced by genotype and the environment is unclear. To explore the stability and adaptability of wheat cultivars with low-Cd accumulation in different environments, we analyzed characteristics based on bioconcentration factor (BCF) and yield data obtained from thirteen low-Cd cultivars grown in ten locations. An additive main effect and multiplicative interaction (AMMI) model with homogeneous grouping based on location type successfully captured the effects of genotype, the environment, and their interaction on low-Cd accumulation stability, with environmental effects (49.62–68.45%) having the greatest influence on the stability of low-Cd accumulation cultivar characteristics. A genotype plus genotype-by-environment interaction (GGE) biplot accurately and intuitively illustrated the adaptability of low-Cd-accumulating wheat cultivars, indicating that the best linear unbiased prediction (BLUP) had a more plausible variation explaining the variance than the means. Here, we identify the cultivars LX99, YN999, JM229, and JM22 as having the best stability and adaptability for low-Cd accumulation by using a heterogeneous linear mixed model with BLUP calculation, combined with cluster and weight analysis. Planting these wheat cultivars with low-Cd accumulation can enable the safe utilization of lightly Cd-contaminated farmland with no reduction in yield. This study extends the application of stability evaluation methods in environmental studies and provides a reference for exploring the stability of other cultivars with low heavy metal accumulation. • Bioconcentration factors of Cd in wheat grain are heterogeneous among locations. • Cd content of low-Cd wheat cultivars is mainly controlled by environmental factors. • AMMI and GGE models can evaluate the low Cd wheat stability and adaptability. • Low-Cd wheat cultivars can absorb less Cd with no yield penalty. [ABSTRACT FROM AUTHOR]