Chemical Basis for Determining the Allelopathic Potential of Invasive Plant Wall Barley (Hordeum murinum L. subsp. murinum).

The study investigated compounds present in the invasive grass Hordeum murinum L. subsp. murinum and tested the allelopathic potential of this plant against common meadow species Festuca rubra L. and Trifolium repens L. Gas chromatography-mass spectrometry (GC-MS) performed separately on the ears and stalks with leaves of wall barley revealed 32 compounds, including secondary metabolites, that may play an important role in allelopathy. Two compounds, N-butylbenzenesulfonamide (NBBS) and diphenylsulfone (DDS), were described for the first time for wall barley and the Poaceae family. The presence of 6,10,14-trimethylpentadecan-2-one (TMP) has also been documented. Aqueous extracts of H. murinum organs (ears and stalks with leaves) at concentrations of 2.5%, 5%, and 7.5% were used to evaluate its allelopathic potential. Compared to the control, all extracts inhibited germination and early growth stages of meadow species. The inhibitory effect was strongest at the highest concentration for both the underground and aboveground parts of the seedlings of the meadow species tested. Comparing the allelopathic effect, Trifolium repens proved to be more sensitive. In light of the results of the study, the removal of wall barley biomass appears to be important for the restoration of habitats where this species occurs due to its allelopathic potential.

Maize straw application reduced cadmium and increased arsenic uptake in wheat and enhanced the rhizospheric bacterial communities in alkaline-contaminated soil.

Many fields where wheat is grown in northern China are co-polluted by arsenic (As) and cadmium (Cd). Thus, remediation of As and Cd-contaminated alkaline soils is crucial for safe wheat production. In this study, a pot experiment was carried out to investigate the impact of 1% and 2% maize straw (MS) incorporation on As and Cd bioavailability, binding forms, uptake by winter wheat (Triticum aestivum L.), and bacterial communities in smelter (SS) and irrigation (IS) alkaline contaminated soils. The results indicated that 2% MS incorporation significantly (p < 0.05) increased bioavailable-As by 37% (SS) and 39% (IS) with no significant change in the bioavailable-Cd in SS2% (31.95%) from 31.95% (SSCK) and IS2% (33.33%) from 32.82% (ISCK). Incorporation of 2% MS increased the grain As concentration from 0.22 mg kg-1 (SSCK) to 0.51 mg kg-1 (SS2%) and from 0.59 mg kg-1 (ISCK) to 0.84 mg kg-1 (IS2%) which is above the acceptable standard of 0.5 mg kg-1 (GB2726-2017). In contrast, the Cd content in grains was maintained at 0.09 (SS1%), 0.04 (SS2%) and 0.03 (IS1%), 0.02 (IS2%) below the acceptable standard of 0.10 mg kg-1 (GB2762-2017). The amendment through dissolved organic carbon mediated As desorption enhanced As transfer to wheat grain, decreasing DTPA-Cd in the soils and its consequent translocation to wheat leaves and grain. The 2% MS incorporation increased the active As fractions, reduced mobile Cd into immobile fractions, and promoted the abundance of Actinobacteria, Bacteroidetes, and Firmicutes in the two soils. These attributes of MS in decreasing the accumulation of Cd in wheat leaves and grains signified its potential as a suitable ingredient for Cd sequestration and food safety in Cd-contaminated soils.

The impact of maize straw incorporation on arsenic and cadmium availability, transformation and microbial communities in alkaline-contaminated soils.

Increasing evidence of the uncertainty of crop straw returning in heavy metal-contaminated soil is a significant concern. The present study investigated the influence of 1 and 2% maize straws (MS) amendment on As and Cd bioavailability in two different alkaline soils (A-industrial and B-irrigation) after 56 days of ageing. Adding MS to the two soils decreased the pH by 1.28 (A soil) and 1.13 (B soil) and increased the concentration of dissolved organic carbon (DOC) by 54.40 mg/kg (A soil) and 100.00 mg/kg (B soil) during the study period. After 56 days of ageing, the overall NaHCO3-As and DTPA-Cd increased by 40% and 33% (A) and 39% and 41% (B) soils, respectively. The MS additions increased the alteration of As and Cd exchangeable and residual fractions, whereas advanced solid-state 13C nuclear magnetic resonance (NMR) revealed that alkyl C and alkyl O-C-O in A soil and alkyl C, Methoxy C/N-alkyl, and alkyl O-C-O in B soil significantly contributed to the As and Cd mobilisation. Collectively, 16 S rRNA analyses revealed Acidobacteria, Firmicutes, Chloroflexi, Actinobacteria and Bacillus promoted the As and Cd mobilisation following the MS addition, while principle component analysis (PCA) demonstrated that bacterial proliferation significantly influenced MS decomposition, resulting in As and Cd mobilisation in the two soils. Overall, the study highlights the implications of applying MS to As- and Cd-contaminated alkaline soil and offers the framework for conditions to be considered during As- and Cd-remediation efforts, especially when MS is the sole remediation component.

Speciation and distribution of chromium (III) in rice root tip and mature zone: The significant impact of root exudation and iron plaque on chromium bioavailability.

Evidence on the contribution of root regions with varied maturity levels in iron plaque (IP) formation and root exudation of metabolites and their consequences for uptake and bioavailability of chromium (Cr) remains unknown. Therefore, we applied combined nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based techniques, micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption near-edge structure (µ-XANES) to examine the speciation and localisation of Cr and the distribution of (micro-) nutrients in rice root tip and mature region. µ-XRF mapping revealed that the distribution of Cr and (micro-) nutrients varied between root regions. Cr K-edge XANES analysis at Cr hotspots attributed the dominant speciation of Cr in outer (epidermal and sub-epidermal) cell layers of the root tips and mature root to Cr(III)-FA (fulvic acid-like anions) (58-64%) and Cr(III)-Fh (amorphous ferrihydrite) (83-87%) complexes, respectively. The co-occurrence of a high proportion of Cr(III)-FA species and strong co-location signals of 52Cr16O and 13C14N in the mature root epidermis relative to the sub-epidermis indicated an association of Cr with active root surfaces, where the dissolution of IP and release of their associated Cr are likely subject to the mediation of organic anions. The results of NanoSIMS (poor 52Cr16O and 13C14N signals), dissolution (no IP dissolution) and µ-XANES (64% in sub-epidermis >58% in the epidermis for Cr(III)-FA species) analyses of root tips may be indicative of the possible re-uptake of Cr by this region. The results of this research work highlight the significance of IP and organic anions in rice root systems on the bioavailability and dynamics of heavy metals (e.g. Cr).

Iron plaque formation, characteristics, and its role as a barrier and/or facilitator to heavy metal uptake in hydrophyte rice (Oryza sativa L.).

The persistent bioavailability of toxic metal(oids) (TM) is undeniably the leading source of serious environmental problems. Through the transfer of these contaminants into food networks, sediments and the aquatic environmental pollution by TM serve as key routes for potential risks to soil and human health. The formation of iron oxyhydroxide plaque (IP) on the root surface of hydrophytes, particularly rice, has been linked to the impact of various abiotic and biotic factors. Radial oxygen loss has been identified as a key driver for the oxidation of rhizosphere ferrous iron (Fe2+) and its subsequent precipitation as low-to-high crystalline and/or amorphous Fe minerals on root surfaces as IP. Considering that each plant species has its unique capability of creating an oxidised rhizosphere under anaerobic conditions, the abundance of rhizosphere Fe2+, functional groups from organic matter decomposition and variations in binding capacities of Fe oxides, thus, impacting the mobility and interaction of several contaminants as well as toxic/non-toxic metals on the specific surface areas of the IP. More insight from wet extraction and advanced synchrotron-based analytical techniques has provided further evidence on how IP formation could significantly affect the fate of plant physiology and biomass production, particularly in contaminated settings. Collectively, this information sets the stage for the possible implementation of IP and related analytical protocols as a strategic framework for the management of rice and other hydrophytes, particularly in contaminated sceneries. Other confounding variables involved in IP formation, as well as operational issues related to some advanced analytical processes, should be considered.

The rhizospheric transformation and bioavailability of mercury in pepper plants are influenced by selected Chinese soil types.

Understanding and prediction of mercury (Hg) phytoavailability in vegetable-soil systems is essential for controlling food chain contamination and safe vegetable production as Hg-contaminated soils pose a serious threat to human health. In this study, four typical Chinese soils (Heilongjiang, Chongqing, Yunnan, and Jilin) with varied physicochemical properties were spiked with HgCl2 to grow sweet pepper (Capsicum annuum L.) in a pot experiment under greenhouse condition. The chemical fractionation revealed a significant decrease in exchangeable Hg, while an increase in organically bound Hg in the rhizosphere soil (RS) compared to bulk soil (BS). This observation strongly highlights the vital role of organic matter on the rhizospheric Hg transformation irrespective of contamination levels and soil properties. Stepwise multiple linear regression (SMLR) analysis between Hg concentration in plants, Hg fractions in RS and BS, and soil properties showed that Hg in plant parts was significantly influenced by soil total Hg (THg) (R2 = 0.90), soil clay (R2 = 0.99), amorphous manganese oxides (amorphous Mn) (R2 = 0.97), amorphous iron oxides (amorphous Fe) (R2 = 0.70), and available Hg (R2 = 0.97) in BS. Nevertheless, in the case of RS, Hg accumulation in plants was affected by soil THg (R2 = 0.99), amorphous Mn (R2 = 0.97), amorphous Fe oxides (R2 = 0.66), soil pH, and organically bound Hg fraction (R2 = 0.96). Among all the evaluated soils (n = 04), metal (mercury) concentration in terms of plant uptake was reported highest in the Jilin soil. Based on SMLR analysis, the results suggested that the phytoavailability of Hg was mainly determined by THg and metal oxides regardless of the rhizospheric effect. These findings facilitate the estimation of Hg phytoavailability and ecological risk that may exist from Hg-contaminated areas where pepper is the dominant vegetable.

Correction: Hashemi et al. Effects of Abiotic Elicitors on Expression and Accumulation of Three Candidate Benzophenanthridine Alkaloids in Cultured Greater Celandine Cells. Molecules 2021, 26, 1395.

The authors wish to make the following correction to the paper [...].

Ecophysiological Parameters of Medicinal Plant Filipendula vulgaris in Diverse Habitat Conditions.

This study attempts to determine which of the habitats occupied by Filipendula vulgaris creates better conditions for its growth and development. Selected physiological parameters-PSII activity, chlorophyll content, electrolyte leakage, hydrogen peroxide content as well as biomass, the occurrence of mycorrhiza, and soil characteristics-were investigated. Grassland soils had a higher content of macronutrients and a lower concentration of heavy metals. The degree of colonization of F. vulgaris by AMF (Arum type) oscillated around high values in both types of stands. Plants growing on xerothermic grasslands achieved much better fluorescence parameters than those collected from meadows. Similar results were obtained from the analysis of chlorophyll content. The destabilization degree of cell membranes was significantly higher in plants collected in meadows than in grasslands. Biomass analysis showed higher values of these parameters in grassland plants. In the case of the parameters of fluorescence emission, plants growing on grasslands achieved significantly lower values than plants collected from meadows. The analyses carried out showed that better conditions for growth and physiological activity of F. vulgaris are probably associated with grasslands on a calcareous substrate.

Mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil-wheat systems.

Soil mercury (Hg) and its bioaccumulation in food crops have attracted widespread concerns globally due to its harmful effects on biota. However, soil mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil-wheat-systems have not been thoroughly explored. Twenty-one (21) soil samples collected throughout China with a wide spectrum of physico-chemical characteristics were contaminated with HgCl2 and winter wheat (Triticum aestivum L.) was grown on the soils in a greenhouse pot-culture experiment for 180 days. A four-step sequential extraction was used segregating soil Hg into water-soluble (F1, 0.21 %), exchangeable (F2, 0.07 %), organically bound (F3, 16.40 %), and residual fractions (F4, 83.32 %). Step-wise multiple linear regression (SMLR) and path analysis (PA) were used to develop a prediction model and identify the major controlling factors of soil-wheat Hg transference. The SMLR results revealed that wheat Hg in leaves, husk, and grain was positively correlated with soil total and available Hg, and crystalline manganese (Cryst-Mn), while negatively correlated with soil pH, amorphous manganese (Amor-Mn) and crystalline aluminium (Cryst-Al). Bioconcentration factor (BCF) values were significantly higher in acidic soils (highest 0.05), with phytotoxic effects in some soils, as compared to alkaline soils (lowest 0.006). Furthermore, wheat grain Hg was significantly correlated with total (R2 = 0.25), water-soluble (R2 = 0.54) and NH4Ac-extractable Hg (R2 = 0.43) while also had a good correlation with soil pH (R2 = -0.20). In conclusion, the soil total and available Hg (water-soluble + exchangeable fraction), pH, organic matter, and Amor-Mn are the most important soil variables that support Hg uptake in the wheat plants, which benefit managing Hg-enriched agricultural soils for safe wheat production.

Significance of Shewanella Species for the Phytoavailability and Toxicity of Arsenic-A Review.

The distribution of arsenic continues due to natural and anthropogenic activities, with varying degrees of impact on plants, animals, and the entire ecosystem. Interactions between iron (Fe) oxides, bacteria, and arsenic are significantly linked to changes in the mobility, toxicity, and availability of arsenic species in aquatic and terrestrial habitats. As a result of these changes, toxic As species become available, posing a range of threats to the entire ecosystem. This review elaborates on arsenic toxicity, the mechanisms of its bioavailability, and selected remediation strategies. The article further describes how the detoxification and methylation mechanisms used by Shewanella species could serve as a potential tool for decreasing phytoavailable As and lessening its contamination in the environment. If taken into account, this approach will provide a globally sustainable and cost-effective strategy for As remediation and more information to the literature on the unique role of this bacterial species in As remediation as opposed to conventional perception of its role as a mobiliser of As.

Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective.

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Arsenic biotransformation and mobilization: the role of bacterial strains and other environmental variables.

Over several decades, arsenic (As) toxicity in the biosphere has affected different flora, fauna, and other environmental components. The majority of these problems are linked with As mobilization due to bacterial dissolution of As-bearing minerals and its transformation in other reservoirs such as soil, sediments, and ground water. Understanding the process, mechanism, and various bacterial species involved in these processes under the influence of some ecological variables greatly contributes to a better understanding of the fate and implications of As mobilization into the environments. This article summarizes the process, role, and various types of bacterial species involved in the transformation and mobilization of As. Furthermore, insight into how Fe(II) oxidation and resistance mechanisms such as methylation and detoxification against the toxic effect of As(III) was highlighted as a potential immobilization and remediation strategy in As-contaminated sites. Furthermore, the significance and comparative advantages of some useful analytical tools used in the evaluation, speciation, and analysis of As are discussed and how their in situ and ex situ applications support assessing As contamination in both laboratory and field settings. Nevertheless, additional research involving advanced molecular techniques is required to elaborate on the contribution of these bacterial consortia as a potential agronomic tool for reducing As availability, particularly in natural circumstances. Graphical abstract. Courtesy of conceptual model: Aminu Darma.

The Allelopathic Potential of Rosa blanda Aiton on Selected Wild-Growing Native and Cultivated Plants in Europe.

Invasive plant species are responsible for changing colonized ecosystems by occupying new areas and creating a threat to the functioning of the native flora and fauna populations. Alien plants can produce allelochemicals, substances completely new to indigenous communities. This study investigated the germination seed reactions of Festuca rubra L. and Raphanus sativus L. var. radicula Pers. cv. Rowa on the extracts from the roots, stalks, leaves, and flowers of Rosa blanda. Aqueous extracts at concentrations of 1%, 2.5%, and 5% were used in order to determine the allelopathic potential of this alien rose for Europe. With the increase in the concentration of extracts, a decrease in the germination capacity of seeds of the tested species was observed. R. blanda extracts inhibited the growth of seedlings. Depending on the concentration and type of the extract, changes in biomass and water content in Red Fescue and Red Radish seedlings were also shown. The highest differences in the electrolyte leakages were noted in seedlings treated with 5% rose extracts. The study showed that the aqueous extracts of R. blanda leaves and flowers had the greatest allelopathic potential.

Effect of Sorbent Additives to Copper-Contaminated Soils on Seed Germination and Early Growth of Grass Seedlings.

Heavy metal and metalloid-contaminated soil is a serious barrier to colonization for many plant species. The problem of the elimination of toxic waste accumulated in technogenous soils in many highly transformed regions is extremely important. Hence, another attempt was made to analyze the effect of the addition of sorbents (BCH-biochar, B-bentonite, ChM-chicken manure, OS-organo-zeolitic substrate) to contaminated copper soil on the germination and early growth of Eurasian common grass species (Agrostis capillaris, A. stolonifera, Festuca rubra and Poa pratensis), which could potentially be used in recultivation. This experiment was based on the laboratory sandwich method. Standard germination indexes, morphometry and biomass analysis were used. The percentage of germinating seeds was lower in each of the soil variants and sorbents used compared to the control. Dry mass was positively stimulated by all sorbents. The response to the addition of sorbents, expressed as the electrolyte leakage of seedlings, was different depending on the species and type of sorbent. Among all sorbents, the most positive effects on germination and growth were observed in the case of OS. Overall, the response to the addition of sorbents was different in the studied species, depending on their stage of development.

Effects of Abiotic Elicitors on Expression and Accumulation of Three Candidate Benzophenanthridine Alkaloids in Cultured Greater Celandine Cells.

Efforts to develop the necessary biotechnologies in Greater Celandine (Chelidonium majus L.), a leading plant resource for the development of plant-derived medicines, have been hampered by the lack of knowledge about transcriptome and metabolome regulations of its medicinal components. Therefore, this study aimed to examine the effect of abiotic elicitors, methyl jasmonate (MJ) and salicylic acid (SA), at different time courses (12, 24, 48, and 72 h), on expression and metabolome of key benzophenanthridine alkaloids (BPAs) in an optimized in vitro culture. Gene expression analysis indicated the upregulation of CFS (cheilanthifoline synthase) to 2.62, 4.85, and 7.28 times higher than the control at 12, 24, and 48 h respectively, under MJ elicitation. Besides, MJ upregulated the expression of TNMT (tetrahydroprotoberberine N-methyltransferase) to 2.79, 4.75, and 7.21 times at 12, 24, and 48 h respectively, compared to the control. Investigation of BPAs revealed a significant enhancement in the chelidonine content (9.86 µg/mg) after 72 h of MJ elicitation. Additionally, sanguinarine content increased to its highest level (3.42 µg/mg) after 24 h of MJ elicitation; however, no significant enhancement was detected in its content in shorter elicitation time courses. Generally, higher gene expression and BPAs' level was observed through longer elicitation courses (48 and 72 h). Our findings take part in improving the understanding of transcription and metabolic regulation of BPAs in cultured Greater Celandine cells.

Effect of Long-Term of He-Ne Laser Light Irradiation on Selected Physiological Processes of Triticale.

In agriculture, the bio-stimulating properties of laser light increase the yielding capacity of crop species. The experiment aimed to determine the pre-sowing effect of irradiation time with laser He-Ne red light of triticale grains (×Triticosecale Wittm. ex A.Camus) on germination and selected morphological and physiological parameters of seedlings and plants grown from them. The highest values of germination indexes were found for grains irradiated with laser for 3 h. In relation to the control, the elongation growth of seedlings was stimulated in grains irradiated with light for 3 h and inhibited for 24 h. The values of the fresh and dry mass of seedlings changed depending on the exposure time. He-Ne light did not significantly affect the degree of destabilization of seedling cell membranes. Biometric analysis of plants grown from irradiated grains showed different reactions of triticale organs to the irradiation time. Red light clearly stimulated the increase in the value of organ mass. Chlorophyll content in leaves was higher in plants grown from grains irradiated for 3 h. Photosynthetic activity did not change significantly relative to the control. The fluorescence emission indexes were mostly lower than in the control, which indicated a positive effect of the laser. In general, the red light of the laser stimulated the morphology and physiology of seedlings and plants, although, for some features, long exposure to red light caused a slight reduction effect.

Effect of Aqueous Extracts from Solidago Canadensis L. Leaves on Germination and Early Growth Stages of Three Cultivars of Raphanus Sativus L. Var. Radicula Pers.

Solidago canadensis L. is an expansive perennial that forms persistent, species-poor plant communities. It often spreads in fallow areas, displacing native floristic ingredients. Its expansiveness is largely due to morphological features, but it can also be the effect of allelopathic interaction. The aim of the experiment was to investigate the effect of aqueous extracts (decoction, infusion, and maceration) from dry S. canadensis leaves on germination and early growth stages of Raphanus sativus L. var. radicula Pers., in three cultivars: 'Rowa', 'Póldluga', and 'Krakowianka'. In comparison to the control, the percentage of germinated radish seeds of 'Rowa' cultivar was statistically lower on the infusion and macerate. Regardless of the cultivar, the smallest changes in germination were found in seeds watered with decoction, and the largest with macerate. Seedlings length was most inhibited on macerate substrates, and least with infusion. Regardless of the form of the extract, each of them negatively affected the initial growth of radish seedlings. A fresh mass of 'Rowa' seedlings was inhibited by all Canadian goldenrod extracts. In relation to the control, the 'Krakowianka' cultivar was the least sensitive to S. canadensis extracts. The total chlorophyll content was the lowest in the seedlings of the 'Rowa' and 'Póldluga' cultivars germinated on macerate, compared to the control and two others extracts. The percentage of electrolyte leakage depended on the type of extract used and the radish cultivar. The study showed that depending on the cultivar, the aqueous extracts from S. canadensis leaves decreasing of germination and early growth of R. sativus.

Do sulfur addition and rhizoplane iron plaque affect chromium uptake by rice (Oryza sativa L.) seedlings in solution culture?

Heavy metal uptake is confined by other elements, namely iron (Fe) and sulfur (S). There are yet no reports on the contribution of S supply to the attenuation of chromium (Cr) uptake when different species of Cr are employed. The bioaccumulation of Cr in two cultivars of rice seedlings subjected to 1.0 mg L-1 Cr (III and VI) stress under S deprived or non-deprived conditions were examined in a hydroponic experiment. Sulfur nutrition promoted the root and shoot growth of rice cultivars under Cr stress. For both + S/ - S seedlings, the concentration of both Cr species followed the sequence ACA (ascorbic citrate acetic) extract > root > shoot, with less Cr accumulated in shoots of + S seedlings to that of - S seedlings. The concentrations of Cr and Fe in ACA extracts were found to be significantly correlated. Compared to + S treatment, Cr and Fe contents in iron plaque without S treatment were markedly reduced, especially for Cr (VI). Cr content in roots and shoots was indicated to be at par between cultivars; however, it significantly differed for S and Cr treatments. The Cr translocation between different parts of plaque-harboring seedlings was more pronounced in Cr (VI) treatment relative to Cr (III) treatment. Increased immobilization of Cr in iron plaque of + S seedlings and its subsequent reduction in aerial tissues may likely shed some light on the barrier function of iron plaques in the uptake of both Cr species by rice seedlings.

The persistence of antimicrobial resistance and related environmental factors in abandoned and working swine feedlots.

Swine feedlots that have operated in the absence of adequate disposal facilities are being demolished under the new environmental protection policies in China. The environmental behavior and transmission risks of antimicrobial resistance genes (ARGs) are unclear for these abandoned swine feedlots. We examined 40 soil samples that originated from the soils adjacent to two abandoned and two working swine feedlots to explore: 1) the distribution patterns and vertical transmission of 17 ARGs and two integron genes and 2) the bacterial community as well as their correlation with environmental factors and target genes. We found that seven and nine out of forty-eight subtypes of veterinary antimicrobials (VAs) were detected in the soil near abandoned feedlots and working feedlots, respectively. Three tet genes (tetM, tetO and tetW) were particularly enriched in the soil adjacent to both abandoned and working feedlots. The tetM gene was a "hub" on the network of the topsoil. The relative abundance of Firmicutes ranged from 2.5 to 9% in the soil near two Beijing feedlots and was significantly higher than that in the upstream blank control (CK soil) (ANOVA, p < 0.05). Overall, the ARG distribution patterns in the soils adjacent to abandoned swine feedlots were similar to the working feedlots. This study offers basic information on the prevalence and transmission risk of ARGs in abandoned swine feedlots and provides a reference for the restoration and reuse of demolished feedlots.

Corrigendum: Impact of Salicylic Acid and PGPR on the Drought Tolerance and Phytoremediation Potential of Helianthus annus.

[This corrects the article DOI: 10.3389/fmicb.2018.02507.].