Antibiotics and antibiotic resistance change bacterial community compositions in marine sediments.

Emerging contaminants, including antibiotics, antibiotic-resistant bacteria (ARB), and extracellular antibiotic resistance genes (eARGs), have been detected in large numbers in the aquatic environment. The effects of emerging contaminants on bacterial communities in marine sediments are not well studied. In this study, the effects of emerging contaminants (antibiotics, ARB, and eARGs) on the variations of bacterial populations in marine sediments of the Bohai Sea, Yellow Sea, East China Sea, and South China Sea were investigated. The results showed that the abundance of the host bacterial phylum Probacteria in the marine sediments of the Bohai Sea was the lowest among the four seas after exposure to different antibiotics, ARB, and eARGs. The inputs of exogenous antibiotics and resistance genes significantly affected the community function, resulting in significant differences in community abundance at the genus level. The abundance of Halomonas, Sulfitobacter, and Alcanivorax in the four sea areas displayed noteworthy differences in response to the addition of exogenous antibiotics and eARGs. These findings contribute to a more comprehensive understanding of the intricate interplay between emerging contaminants and the dynamics of bacterial communities in natural ecosystems.

Foliar application of selenium nanoparticles alleviates cadmium toxicity in maize (Zea mays L.) seedlings: Evidence on antioxidant, gene expression, and metabolomics analysis.

The molecular and metabolic mechanisms of foliar selenium (Se) nanoparticles (SeNPs) application in mitigating cadmium (Cd) toxicity in crops have not been well studied. Herein, hydroponically cultured maize seedlings were exposed to Cd (20 µM) and treated without and with foliar SeNPs application. Effects of SeNPs on Cd transporter genes and plant metabolism were also explored. Results showed that compared to control plants without Cd exposure, Cd exposure decreased shoot height (16.8 %), root length (17.7 %), and fresh weight of root (24.2 %), stem (28.8 %), and foliar-applied leaves (Se-leaves) (15.0 %) via oxidative damage. Compared to Cd exposure alone, foliar SeNPs application at 20 mg/L (0.25 mg/plant) significantly alleviated the Cd toxicity by promoting photosynthesis and antioxidant capacity and fixing Cd in cell wall. Meanwhile, the mineral concentration of Ca (26.0 %), Fe (55.4 %), Mg (27.0 %), Na (28.6 %), and Zn (10.1 %) in Se-leaves was improved via foliar SeNPs application at 20 mg/L. QRT-PCR analysis further revealed that down- and up-regulation of the expression of ZmHMA2 and ZmHMA3 gene in Se-leaves contributed to reduced translocation of Cd in plants and enhanced Cd sequestration in the vacuole, respectively. Metabolomic results further indicated that metabolic pathways including carbohydrate metabolism, membrane transport, translation, amino acid metabolism, and energy metabolism were significantly affected by foliar SeNPs application. In conclusion, foliar SeNPs application at 20 mg/L could be a prospective strategy to mitigate Cd toxicity in maize.

Agronomic and ionomics indicators of high-yield, mineral-dense, and low-Cd grains of wheat (Triticum aestivum L.) cultivars.

The accumulation of toxic and essential nutrient elements in wheat grain influences wheat yield, grain nutritional quality, and human health. Here, we assessed the potential for breeding wheat cultivars to combine high yield with low cadmium and high iron and/or zinc concentrations in grains, and we screened appropriate cultivars. A pot experiment was conducted to explore differences in grain cadmium, iron, and zinc concentrations among 68 wheat cultivars, as well as their relationships with other nutrient elements and agronomic characters. The results showed 2.04-, 1.71-, and 1.64-fold differences in grain cadmium, iron, and zinc concentrations, respectively, among the 68 cultivars. Grain cadmium concentration was positively correlated with grain zinc, iron, magnesium, phosphorus, and manganese concentrations. Grain copper concentration was positively correlated with grain zinc and iron concentrations, but not with grain cadmium concentration. Therefore, copper has a potential role in regulating grain iron and zinc accumulation without influencing cadmium concentration in wheat grain. There were no significant relationships between grain cadmium concentration and four important wheat agronomic characters (i.e., grain yield, straw yield, thousand kernel weight, and plant height), indicating that the breeding of low-cadmium-accumulating cultivars with dwarfism and high yield characteristics is possible. On cluster analysis, four cultivars (Ningmai11, Xumai35, Baomai6, and Aikang58) exhibited low-cadmium and high-yield characteristics. Among them, Aikang58 contained moderate iron and zinc concentrations, while Ningmai11 had relatively high iron but low zinc concentrations in the grain. These results imply that it is feasible to breed high-yield dwarf wheat with low cadmium and moderate iron and zinc concentrations in the grain.

Sulfur reduces the root-to-shoot translocation of arsenic and cadmium by regulating their vacuolar sequestration in wheat (Triticum aestivum L.).

Accumulation of arsenic (As) and cadmium (Cd) in wheat grain is a serious threat to human health. Sulfur (S) can simultaneously decrease wheat grain As and Cd concentrations by decreasing their translocation in wheat; however, the mechanisms are unclear. We conducted hydroponic experiments to explore the mechanisms by which S modulates As and Cd translocation and their toxicity in wheat. Wheat seedlings were grown in deficient sulfate (2.5 µM) or sufficient sulfate (1.0 mM) nutrient solutions for 6 days and then exposed to zero (control), low As+Cd (1 µM As plus 0.5 µM Cd), or high As+Cd (50 µM As plus 30 µM Cd) for another 6 days. Compared with the control, plant growth was not affected by low As+Cd, but was significantly inhibited by high As+Cd. In the low As+Cd treatment, S supply had no significant effect on plant growth or root-to-shoot As and Cd translocation. In the high As+Cd treatment, sufficient S supply significantly alleviated As and Cd toxicity and their translocation by increasing phytochelatin (PC) synthesis and the subsequent vacuolar sequestration of As and Cd in roots, compared with deficient S supply. The use of L-buthionine sulfoximine (a specific inhibitor of γ-glutamylcysteine synthetase) confirmed that the alleviation of As and Cd translocation and toxicity in wheat by S is mediated by increased PC production. Also, TaHMA3 gene expression in wheat root was not affected by the As+Cd and S treatments, but the expression of TaABCC1 was upregulated by the high As+Cd treatment and further increased by sufficient S supply and high As+Cd treatment. These results indicate that S-induced As and Cd subcellular changes affect As and Cd translocation mainly by regulating thiol metabolism and ABCC1 expression in wheat under As and Cd stress.

The effect of organic solvent washing on the structure of hydrochar-based dissolved organic matters and its potential environmental toxicity.

With the increased interest in the practical use of hydrochar, concerns about the possible environmental biotoxicity of hydrochar and its released dissolved organic matters (DOM) have grown. As a common method for removing bio-oil on the surface of hydrochar, the effect of organic solvent washing on the properties of hydrochar released DOM remains unclear. In this study, we made a comprehensive comparison of hydrochar properties and molecule structure as well as biotoxicity of DOM released from HC (raw hydrochar) and THC (hydrochar washed by tetrahydrofuran). The results indicated that the mass loss of hydrochar was obvious after tetrahydrofuran (THF) washing, and a decline of H/C atomic ratio and increase of N/C and O/C atomic ratios was observed based on Van Krevelen (VK) diagram. This result was further confirmed by FTIR, 13C NMR, and XPS results. Meanwhile, the molecule structure of DOM was shifted to lower molecule weight with higher O-contain compounds after THF extraction due to the demethanation process. However, the biotoxicity experiments indicated that both extracted DOM had no significant impact on germination rate of wheat, and HC-treated sample even exhibited growth superiority. Nevertheless, potential toxicity was observed with the increase of the activity of antioxidant enzymes, and THF washing aggravated the potential oxidative damage through increasing the aromaticity of DOM. Such understanding highlights the importance of evaluating hydrochar and its released DOM before applications, so as to reduce the potential environment biotoxicity.

Sulfate application decreases translocation of arsenic and cadmium within wheat (Triticum aestivum L.) plant.

Arsenic (As) and cadmium (Cd) typically exhibit divergent fates in soil, which complicates efforts to decrease As and Cd accumulation in the edible parts of crops. Here, we performed pot experiments to examine the effect of sulfate application on As and Cd accumulation in the grain of wheat grown in contaminated soil. Compared to the control (no sodium sulfate addition), application of 120 mg kg-1 sodium sulfate decreased the rhizosphere soil pH from 7.27 to 7.10 and increased the soil extractable Cd concentration; however, it did not significantly influence the soil extractable As concentration. However, sodium sulfate addition decreased As and Cd concentrations in wheat grain, in association with decreased As and Cd translocation from root and straw to grain, rather than from soil to root. Furthermore, sodium sulfate addition significantly decreased membrane lipid peroxidation and enhanced photosynthesis, while increasing the uptake of nitrogen, phosphorus, and sulfur. These effects increased the growth and grain weight of plants grown in As and Cd co-contaminated soil. Our findings provide insight into the mechanisms by which sulfate modulates As and Cd uptake and translocation in wheat; moreover, our findings will enable formulation of strategies to decrease As and Cd concentrations in the grain of wheat grown in As and Cd co-contaminated soil.

Effect of elemental sulfur and gypsum application on the bioavailability and redistribution of cadmium during rice growth.

Recently, concerns over heavy metal contamination of soil have grown. The application of sulfur has been recommended to enhance crop productivity and increase soil cadmium (Cd) immobilization. In this study, a pool experiment was conducted to investigate the effects of two sulfur sources and multiple treatment levels on rice growth and Cd accumulation. The two sulfur forms were elemental sulfur (S0) and gypsum, both of which were applied at 0, 0.15, and 0.30 g S kg-1 soil, for a total of five treatments. The results showed that both S0 and gypsum significantly increased rice biomass compared to the control (CK), and rice yield was increased 2.8-4.8 folds. The effect size was greater for gypsum than S0. The application of S0 reduced the rice grain Cd concentration from 0.61 mg kg-1 (CK) to 0.41-0.46 mg kg-1, while gypsum reduced the Cd concentration to 0.24-0.43 mg kg-1. The lower gypsum application level achieved the greatest reduction in rice grain Cd accumulation. This study further demonstrated that the application of S0 and gypsum led to a decrease in the labile Cd percentage and an increase in the stable Cd percentage. In bulk soil, iron and manganese oxide-bound Cd increased by 6.4-7.3% and 0.7-2.0% for the S0 and gypsum treatments, respectively. In the rhizosphere, residual Cd increased by >0.6%. Furthermore, this study found that sulfur application reduced Cd transfer from root to shoot, and significantly decreased rice grain Cd accumulation. These findings indicate that sulfur application to paddy soils can promote rice productivity and effectively remediate soil Cd contamination, with a greater effect by gypsum than S0.

Low arsenate influx rate and high phosphorus concentration in wheat (Triticum aestivum L.): A mechanism for arsenate tolerance in wheat plants.

Two wheat (Triticum aestivum L.) cultivars differing in arsenic (As)-tolerance were used to investigate the effects of phosphorus (P) concentration and nutrient solution pH on As(V) toxicity and As(V) uptake kinetics, and to illustrate the mechanism of As(V) tolerance in wheat seedlings. Low pH and low phosphate concentration enhanced wheat uptake of As, resulting in high As toxicity. The As(V)-tolerant cultivar MM45 exhibited higher relative root elongation than non-tolerant cultivar HM29 in all treatments, except that no genotypic difference was recorded for the solution P at 100 µmol L-1 or greater. Wheat seedling As(V) tolerance was positively correlated with P concentration in roots and shoots. In short-term (30 min) As(V)-uptake kinetics experiments, the maximum influx rate (Vmax) of As(V) increased with decreasing solution pH (from 7.0 to 6.0). Compared with HM29, although MM45 had lower Vmax, its Michaelis-Menten constant (Km) did not exceed that of HM29 in all treatments. The Vmax values of both cultivars were not significantly affected by phosphate treatments, except for HM29 which had significantly higher Vmax value in the presence of phosphate at pH 7.0. The Km values of the two cultivars increased by 9- to 20-fold when phosphate was present as opposed to absent from the uptake solution. This study showed that the Vmax values are mainly increased by high pH and As(V) uptake Km is mainly increased by phosphate presence. Decreased As(V) influx rates during early stages and increased P concentration in plant tissues are associated with increased As tolerance in wheat seedlings.

Short-term biochar manipulation of microbial nitrogen transformation in wheat rhizosphere of a metal contaminated Inceptisol from North China plain.

While metal immobilization had been increasingly reported with biochar soil amendment (BSA), changes in microbial activity and nitrogen (N) transformation in metal contaminated croplands following biochar addition had been insufficiently addressed. In a field experiment, a Pb/Cd contaminated Inceptisol from North China was amended to topsoil with wheat straw biochar at 0 (CK), 20 (C1) and 40 t ha-1 (C2). The changes within two years following BSA were tested in microbial biomass and respiration, and in abundance of N transforming microbial communities and their activities. Corresponding to the results of decreased soil extractable Cd and Pb, significant reductions in qCO2 were found in rhizosphere and bulk soil only under C2 in the first year. The potential nitrification activity was significantly increased by 20-71%, along with an increase in ammonium (by 7-21%) and nitrate (by 21%-70%) concentration, with BSA compared to CK. Meanwhile, N2O production activity was slightly increased (by up to 20%) but N2O reduction activity greatly enhanced (by up to 84%), with a higher ratio of nosZ/(nirS + nirK), under C2 in rhizosphere in both wheat seasons. Whereas, such changes were not remarkable in bulk soil. Moreover, microbial communities were less respondent to biochar in the second year following the addition. Therefore, microbial growth and functioning for N transforming and cycling in metal contaminated soils could be largely improved with BSA at 40 t ha-1. Of course, studies are still deserved to mimic the long term changes with biochar in N cycling of the metal contaminated dry croplands.

Exogenous GR24 Alleviates Cadmium Toxicity by Reducing Cadmium Uptake in Switchgrass (Panicum virgatum) Seedlings.

Strigolactones (SLs) are classified into plant hormones, playing a key role as a mediator of plant growth in response to several abiotic stresses, including drought and salinity. However, the role of SLs in cadmium (Cd)-induced stress to plants is still unknown. The physiological responses of switchgrass (Panicum virgatum) stressed in 10 µmol L-1 Cd to exogenous synthetic SLs analog, GR24 were studied in hydroponics. The Cd stress significantly caused the adverse effects on plant growth and root morphology, inhibited photosynthesis, but boosted lipid peroxidation of Switchgrass seedlings. After treatment of 1 µmol L-1 GR24, the above adverse effects caused by Cd stress were significantly alleviated, mainly reflects in improvement of shoot biomass, relative water content, root development, chlorophyll contents, activities of typical antioxidant enzymes, nutrient uptake. The reason for exogenous GR24 alleviating cadmium toxicity might be owing to that exogenous GR24 promoted the content of endogenous SLs, increased some essential element Fe (iron), Zn (zinc), Mn (manganese) and Cu (copper) uptake and reduced cadmium uptake, accumulation and partition in shoot of switchgrass seedlings.