Xylem-based long-distance transport and phloem remobilization of copper in Salix integra Thunb

Environmental efficacy of polyethylene microplastics: Enhancing the solidification of CuO nanoparticles and reducing the physiological toxicity to peanuts

Microplastics and metal-based nanoparticles (NPs) are environmental pollutants that have attracted significant attention. However, there have been relatively few studies on the combined pollution of these substances in the soil-plant system. To investigate the environmental impact and interaction mechanisms of these two pollutants, a pot experiment was conducted to examine the effects of soil exposure on peanut growth. The experiment results revealed that polyethylene (PE) had a minimal effect on peanut growth, while CuO NPs significantly inhibited peanut growth. Peanut biomass decreased by over 50 % in all Cu treatments. The presence of PE significantly impacted the dissolution and absorption of CuO NPs. When 0.5 % PE was present, the dissolution and transformation of CuO NPs were limited, resulting in a total Cu concentration of 458 mg/kg. Conversely, when 5 % PE was present, the dissolution and transformation of CuO NPs were promoted, leading to a DTPA-Cu concentration of 141 mg/kg, the highest level observed. The distribution of trace elements in peanut stems also responded to the differences in Cu concentration. Both pollutants significantly disrupted soil bacteria, with CuO NPs having a more pronounced effect than PE. Throughout the entire growth cycle of peanuts, no chemical adsorption occurred between PE and CuO NPs, and CuO NPs had no significant impact on the aging rate of PE. In summary, this study provides insights into the environmental impact and transport mechanisms of composite pollution involving microplastics and metal-based nanoparticles in the soil-peanut system.

Sewage Sludge Promotes the Accumulation of Antibiotic Resistance Genes in Tomato Xylem

Xylem serves as a conduit linking soil to the aboveground plant parts and facilitating the upward movement of microbes into leaves and fruits. Despite this potential, the composition of the xylem microbiome and its associated risks, including antibiotic resistance, are understudied. Here, we cultivated tomatoes and analyzed their xylem sap to assess the microbiome and antibiotic resistance profiles following treatment with sewage sludge. Our findings show that xylem microbes primarily originate from soil, albeit with reduced diversity in comparison to those of their soil microbiomes. Using single-cell Raman spectroscopy coupled with D2O labeling, we detected significantly higher metabolic activity in xylem microbes than in rhizosphere soil, with 87% of xylem microbes active compared to just 36% in the soil. Additionally, xylem was pinpointed as a reservoir for antibiotic resistance genes (ARGs), with their abundance being 2.4-6.9 times higher than in rhizosphere soil. Sludge addition dramatically increased the abundance of ARGs in xylem and also increased their mobility and host pathogenicity. Xylem represents a distinct ecological niche for microbes and is a significant reservoir for ARGs. These results could be used to manage the resistome in crops and improve food safety.

The response of physiological and xylem anatomical traits under cadmium stress in Pinus thunbergii seedlings

Studying the response of physiological and xylem anatomical traits under cadmium stress is helpful to understand plants' response to heavy metal stress. Here, seedlings of Pinus thunbergii Parl. were treated with 50, 100 and 150 mg kg-1 Cd2+ for 28 days. Cadmium and nonstructural carbohydrate content of leaves, stems and roots, root Cd2+ flux, cadmium distribution pattern in stem xylem and phloem, stem xylem hydraulic traits, cell wall component fractions of stems and roots, phytohormonal content such as abscisic acid, gibberellic acid 3, molecule -indole-3-acetic acid, and jasmonic acid from both leaves and roots, as well as xylem anatomical traits from both stems and roots were measured. Root Cd2+ flux increased from 50 to 100 mmol L-1 Cd2+ stress, however it decreased at 150 mmol L-1 Cd2+. Cellulose and hemicellulose in leaves, stems and roots did not change significantly under cadmium stress, while pectin decreased significantly. The nonstructural carbohydrate content of both leaves and stems showed significant changes under cadmium stress while the root nonstructural carbohydrate content was not affected. In both leaves and roots, the abscisic acid content significantly increased under cadmium stress, while the gibberellic acid 3, indole-3-acetic acid and jasmonic acid methylester content significantly decreased. Both xylem specific hydraulic conductivity and xylem water potential decreased with cadmium stress, however tracheid diameter and double wall thickness of the stems and roots were not affected. High cadmium intensity was found in both the stem xylem and phloem in all cadmium stressed treatments. Our study highlighted the in situ observation of cadmium distribution in both the xylem and phloem, and demonstrated the instant response of physiological traits such as xylem water potential, xylem specific hydraulic conductivity, root Cd2+ flux, nonstructural carbohydrate content, as well as phytohormonal content under cadmium stress, and the less affected traits such as xylem anatomical traits, cellulose and hemicellulose.

Tissue-specific distribution and bioaccumulation of perfluoroalkyl acids, isomers, alternatives, and precursors in citrus trees of contaminated fields: Implication for risk assessment

The ingestion of fruits containing perfluoroalkyl acids (PFAAs) presents potential hazards to human health. This study aimed to fill knowledge gaps concerning the tissue-specific distribution patterns and bioaccumulation behavior of PFAAs and their isomers, alternatives, and precursors (collectively as per-/polyfluoroalkyl substances, PFASs) within citrus trees growing in contaminated fields. It also assessed the potential contribution of precursor degradation to human exposure risk of PFASs. High concentrations of total target PFASs (∑PFASstarget, 92.45-7496.16 ng/g dw) and precursors measured through the total oxidizable precursor (TOP) assay (130.80-13979.21 ng/g dw) were found in citrus tree tissues, and short-chain PFASs constituted the primary components. The total PFASs concentrations followed the order of leaves > fruits > branches, bark > wood, and peel > pulp > seeds. The average contamination burden of peel (∑PFASstarget: 57.75%; precursors: 71.15%) was highest among fruit tissues. Bioaccumulation factors (BAFs) and translocation potentials of short-chain, branched, or carboxylate-based PFASs exceeded those of their relatively hydrophobic counterparts, while ether-based PFASs showed lower BAFs than similar PFAAs in above-ground tissues of citrus trees. In the risk assessment of residents consuming contaminated citruses, precursor degradation contributed approximately 36.07% to total PFASs exposure, and therefore should not be ignored.

Mutation of OsNRAMP5 reduces cadmium xylem and phloem transport in rice plants and its physiological mechanism

Natural resistance associated macrophage protein 5 (NRAMP5) is a key transporter for cadmium (Cd) uptake by rice roots; however, the effect of OsNRAMP5 on Cd translocation and redistribution in rice plants remains unknown. In this study, an extremely low Cd-accumulation mutant (lcd1) and wild type (WT) plants were utilized to investigate the effect of OsNRAMP5 mutation on Cd translocation and redistribution via the xylem and phloem and its possible physiological mechanism using field, hydroponic and isotope-labelling experiments. The results showed that OsNRAMP5 mutation reduced xylem and phloem transport of Cd, due to remarkably lower Cd translocation from roots to shoots and from the leaves Ⅰ-Ⅲ to their corresponding nodes, as well as lower Cd concentrations in xylem and phloem sap of lcd1 compared to WT plants. Mutation of OsNRAMP5 reduced Cd translocation from roots to shoots in lcd1 plants by increasing Cd deposition in cellulose of root cell walls and reducing OsHMA2-and OsCCX2-mediated xylem loading of Cd, and the citric acid- and tartaric acid-mediated long-distance xylem transport of Cd. Moreover, OsNRAMP5 mutation inhibited Cd redistribution from flag leaves to nodes and panicles in lcd1 plants by increasing Cd sequestration in cellulose and vacuoles, and decreasing OsLCT1-mediated Cd phloem transport in flag leaves.

The translocation and fractionation of rare earth elements (REEs) via the phloem in Phytolacca americana L

Rare earth elements (REEs) are considered to be emerging contaminants due to their widespread use and lack of recycling. Phytolacca americana L. has great potential for REEs phytoextraction. Our understanding of REEs in P. americana focuses mostly on root absorption and xylem translocation, but the role of phloem translocation has received little attention. In this research, the translocation and fractionation of REEs from phloem to organs in P. americana were investigated. In addition, the effect of organic acids in the REEs translocation via phloem exudates was also examined. The results showed that REEs could transport bidirectionally via the phloem, and 86% of REEs exported from old leaves could move downwards to the root, whereas only 14% of them transported upwards to the young leaves. Heavy rare earth elements (HREEs) enrichment was found in the REEs fractionation processes both from phloem to leaf and from stem to root, indicating that HREEs were preferentially transferred not only down to roots, but also up to the young leaves. The concentration of oxalic acid in phloem exudates was much higher than other organic acids. 94.7% oxalic acid in phloem exudates was preferred to combine with REEs, especially HREEs. Additionally, the concentrations of HREEs had a high positive correlation with oxalic acid in phloem exudates, which demonstrated oxalic acid may play a significant role in the long-distance transport of HREEs in phloem. In conclusion, HREEs have higher translocation ability than light rare earth elements (LREEs) in both xylem and phloem of P. americana. As far as we know, this is the first report focused on the phloem translocation and redistribution of REEs in P. americana, which provides a valuable understanding of the mechanism for phytoremediation of REEs contaminated soils.

New Insights into the Accumulation, Transport, and Distribution Mechanisms of Hexafluoropropylene Oxide Homologues, Important Alternatives to Perfluorooctanoic Acid, in Lettuce (Lactuca sativa L.)

Hexafluoropropylene oxide (HFPO) homologues, which are important alternatives to perfluorooctanoic acid, have been frequently identified in crops. Although exposure to HFPO homologues via crops may pose non-negligible threats to humans, their impact on crops is still unknown. In this study, the accumulation, transport, and distribution mechanisms of three HFPO homologues in lettuce were investigated at the plant, tissue, and cell levels. More specifically, HFPO trimer acid and HFPO tetramer acid were primarily fixed in roots and hardly transported to shoots (TF, 0.06-0.63). Conversely, HFPO dimer acid (HFPO-DA) tended to accumulate in lettuce shoots 2-264 times more than the other two homologues, thus resulting in higher estimated daily intake values. Furthermore, the dissolved organic matter derived from root exudate enhanced HFPO-DA uptake by increasing its desorption fractions in the rhizosphere. The transmembrane uptake of HFPO homologues was controlled by means of a transporter-mediated active process involving anion channels, with the uptake of HFPO-DA being additionally facilitated by aquaporins. The higher accumulation of HFPO-DA in shoots was attributed to the larger proportions of HFPO-DA in the soluble fraction (55-74%) and its higher abundance in both vascular tissues and xylem sap. Our findings expand the understanding of the fate of HFPO homologues in soil-crop systems and reveal the underlying mechanisms of the potential exposure risk to HFPO-DA.

Uptake of heavy metals by crops near a mining field: Pathways from roots and leaves

Metal uptake and distribution in crops have been demonstrated to be highly variable and depending on the metal of interest and the crop type. However, no consensus is reached regarding the primary factor controlling metal uptake in crops. This study thus comparably investigated Hg, As, Zn, Pb, Cd and Cu uptake and distribution in three crops grown in a watershed near a copper mining field located in Yunnan, Southwestern China. The bioconcentration factor (BCF) and translocation factor (TF) were statistically compared for the same metal across different crops. Leafy crops had a stronger propensity to accumulate Hg, As and Zn than fruit crops. The ability of grain crops to accumulate Cd and Cu was much lower than leafy and fruit crops. The three crops all tended not to accumulate Pb in their edible tissues. The DTPA extracted metal concentrations were not statistically correlated with the metal concentrations in crop edible tissues. It is thus not practical to predict metal uptake of Hg, As, Pb and Zn through their available concentrations in soils. The contents of nitrogen and phosphorus, and competing metal ions present in paddy soil decreased the accumulation of Cu and Cd in rice grains. By means of hierarchical cluster analysis, the high accumulation of Zn in the edible tissues of fruit and grain crops was mainly due to dust inputs via phloem transport from leaves. This is why BCF(Zn) was the highest among the six metals for these two crops. For leafy crops, the accumulation of Hg, Cd and Zn in leaves was mainly through soil inputs by roots. Our findings serve as a scientific basis for the selection of crops in areas with high background of heavy metals.

Recovery after deficiency: systemic copper prioritization and partitioning in the leaves and stems of hybrid poplar

Copper (Cu) is important for many aspects of plant function including photosynthesis. It has been suggested that photosynthesis, especially in young leaves, is prioritized for Cu delivery after deficiency in hybrid poplar. To determine relative Cu delivery prioritization, we enriched hydroponic plant growth media of Cu-deficient poplar with 98% 65Cu and tracked Cu delivery after deficiency to young leaves, mature leaves and stems. Young leaves acquired ~58% more 65Cu on Day 1 and ~65% more 65Cu by Day 3 compared with mature leaves. Additionally, stomatal conductance (gs) was measured on leaves for 6 weeks and during a 3-day 65Cu pulse resupply period. During deficiency, mature leaves maintained a higher gs than younger leaves but 3 days after Cu resupply the younger leaves that had recovered showed the highest gs. In conclusion, these results provide a quantitative understanding of how Cu is systemically transported and distributed to photosynthetic and stem tissues.

Mapping the sex determination region in the Salix F1 hybrid common parent population confirms a ZW system in six diverse species

Within the genus Salix, there are approximately 350 species native primarily to the northern hemisphere and adapted to a wide range of habitats. This diversity can be exploited to mine novel alleles conferring variation important for production as a bioenergy crop, but also to identify evolutionarily important genes, such as those involved in sex determination. To leverage this diversity, we created a mapping population by crossing 6 Salix species (Salix viminalis, Salix suchowensis, Salix integra, Salix koriyanagi, Salix udensis, and Salix alberti) to common male and female Salix purpurea parents. Each family was genotyped via genotyping-by-sequencing and assessed for kinship and population structure as well as the construction of 16 backcross linkage maps to be used as a genetic resource for breeding and selection. Analyses of population structure resolved both the parents and F₁ progeny to their respective phylogenetic section and indicated that the S. alberti parent was misidentified and was most likely S.suchowensis. Sex determining regions were identified on Salix chromosome 15 in the female-informative maps for seven of the eight families indicating that these species share a common female heterogametic ZW sex system. The eighth family, S. integra × S. purpurea, was entirely female and had a truncated chromosome 15. Beyond sex determination, the Salix F₁ hybrid common parent population (Salix F₁ HCP) introduced here will be useful in characterizing genetic factors underlying complex traits, aid in marker-assisted selection, and support genome assemblies for this promising bioenergy crop.

Phytoremediation potential evaluation of multiple Salix clones for heavy metals (Cd, Zn and Pb) in flooded soils

Climate-induced flooding makes soil more vulnerable to heavy metal contamination, posing challenges for soil remediation. Salix has the potential to cope with flooding stress and environmental contamination, but its effectiveness in flooded soils with multiple heavy metals has not yet been well assessed. Thus, the present work tested fifteen Salix clones grown in multimetal (Cd, Zn and Pb) contaminated soils under non-flooded versus flooded conditions. The results indicated that all tested Salix clones withstood long-term (90 d) flooding. Compared to the non-flooded condition, the flooded condition reduced the Cd (11.7-90.1%) contents in all organs but dramatically increased the Zn and Pb contents in the roots. The bioconcentration factor values of heavy metals in the aboveground organs were in the order of Cd > Zn > Pb. The tested Salix clones were characterized by high phytoextraction capacity for Cd and Zn under non-flooded condition and phytostabilization trait for Pb under flooded condition. To assess the overall performance of phytoremediation potentials, we attempted to use an analytic hierarchy process-entropy weight (AHP-EW) model, which considered the growth performance, photosynthetic parameters, accumulation, and mobility of toxic metals. Three Salix clones (J1010, P54 and P667) exhibited significant potential for multimetal remediation capacities. The current study provided valuable insights into the phytomanagement of woody plants, and the AHP-EW model is helpful for screening suitable trees for the phytoremediation of heavily multimetal contaminated wetlands.

Effects of copper oxide nanoparticles on Salix growth, soil enzyme activity and microbial community composition in a wetland mesocosm

A model wetland with Salix was established to investigate the effects of CuO nanoparticles (NPs; the equivalent amount of Cu at 0, 100 and 500 mg/kg) on plant, soil enzyme activity and microbial community. Ionic Cu (100, 500 mg/kg) and bulk-sized CuO particles (BPs, 500 mg/kg) were included as controls. The results suggested the CuO NPs at 500 mg/kg and ionic Cu treatments inhibited the plant growth, while CuO NPs at 100 mg/kg and CuO BPs at 500 mg/kg played a facilitating role. CuO NPs significantly decreased the activities of peroxidase and polyphenol oxidase, while ionic Cu treatments increased peroxidase activity, BPs and ionic Cu (500 mg/kg) increased the polyphenol oxidase activity. Bacterial community richness and diversity were reduced in all Cu treatments; however, CuO NPs and BPs at 500 mg/kg significantly increased the richness and diversity of fungal community.Soil microbial community was significantly altered by Cu types and dose. In comparison with ionic Cu and CuO BPs, CuO NPs uniquely enriched the microbial community and the fungal families.Overall, it demonstrate that both particle size and dose regulate the impact of CuO on wetland ecology, which deepens our understanding on the ecological risks of CuO NPs in freshwater forested wetland.

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

A Smart and Sustainable Future for Viticulture Is Rooted in Soil: How to Face Cu Toxicity

In recent decades, agriculture has faced the fundamental challenge of needing to increase food production and quality in order to meet the requirements of a growing global population. Similarly, viticulture has also been undergoing change. Several countries are reducing their vineyard areas, and several others are increasing them. In addition, viticulture is moving towards higher altitudes and latitudes due to climate change. Furthermore, global warming is also exacerbating the incidence of fungal diseases in vineyards, forcing farmers to apply agrochemicals to preserve production yields and quality. The repeated application of copper (Cu)-based fungicides in conventional and organic farming has caused a stepwise accumulation of Cu in vineyard soils, posing environmental and toxicological threats. High Cu concentrations in soils can have multiple impacts on agricultural systems. In fact, it can (i) alter the chemical-physical properties of soils, thus compromising their fertility; (ii) induce toxicity phenomena in plants, producing detrimental effects on growth and productivity; and (iii) affect the microbial biodiversity of soils, thereby influencing some microbial-driven soil processes. However, several indirect (e.g., management of rhizosphere processes through intercropping and/or fertilization strategies) and direct (e.g., exploitation of vine resistant genotypes) strategies have been proposed to restrain Cu accumulation in soils. Furthermore, the application of precision and smart viticulture paradigms and their related technologies could allow a timely, localized and balanced distribution of agrochemicals to achieve the required goals. The present review highlights the necessity of applying multidisciplinary approaches to meet the requisites of sustainability demanded of modern viticulture.

The effect of particle size of bamboo biochar on the phytoremediation of Salix psammophila C. to multi-metal polluted soil

Biochar shows great potential in soil remediation. The benefits of biochar on soil depend onits intrinsic properties and soil characteristics. However, the influence of particle sizes of biochar on soil remediation is not clear. In a pot experiment, we evaluated the effects of bamboo biochar (BBC) particle sizes (P1 < 0.15 mm, 0.15 mm < P2 < 0.25 mm, 0.25 mm < P3 < 0.50 mm) on phytoremediation efficiency of Salix psammophila C. cultivated in multi-metal polluted soil. We added the BBC at 3% (w/w) in tested soil. Next, the BBC was thoroughly mixed with soil and weighting to the pot, and S. psammophila cuttings were planted and grown for six months in the amended soil under model growth condition.Results revealed the addition of different sizes of BBC particles affected soil quality, plant growth, and HMs accumulation in plants. All sizes of BBC treatments improved Cd and Zn accumulation, whereas plants in P2 treatment showed the greatest accumulation, increased by 52.41 and 25.55% compared with the control (1,503 and 19,928 μg·plant^-1). Overall, the results indicated BBC enhanced the phytoremediation efficiency of S. psammophila. Plants cultivated in P2 treatment showed the most significant effect on remediating contaminated soil.

Impacts of bamboo biochar on the phytoremediation potential of Salix psammophila grown in multi-metals contaminated soil

We investigated the effects of bamboo biochar (BBC) as soil amendment on growth and phytoremediation potential of Salix psammophila in soil heavily polluted by Cd and Zn. Bamboo biochar was added to soil at ratios ranging from 1 to 7% (w/w), which significantly increased the organic matter, available potassium (K) content, while decreased the hydrolyzable nitrogen (N) content and the levels of total and bioavailable HMs in soil. The BBC amendment at ratios of 1% to 5% showed little effect on growth of plant, whereas at 7% ratio significantly decreased biomass compared to the control. BBC amendment stimulated the accumulation of Cu, Cd and Zn in plant tissues, meanwhile, Cd and Zn accumulation were more evident, especially in the BBC-3% treatment. BBC amendment improved the TF and BCF values of Cd, Zn and Cu compared to control. Higher BCF for Cd (BCF >1) and TF for Zn (TF >1) values indicate Salix psammophila have considerable potential for phytoremediation efficiency in BBC amended soil treatment. This study provides practical evidence of the efficient BBC-assisted phytoremediation capability of Salix psammophila and highlights its potential as a viable and inexpensive approach for in situ remediation.