Effect of cadmium on growth, photosynthesis, mineral nutrition and metal accumulation of bana grass and vetiver grass

Effects of nitrogen regulation on heavy metal phytoextraction efficiency (Leucaena leucocephala): Application of a nitrogen fertilizer and a fungal agent

Lead (Pb) and cadmium (Cd) have been identified as the primary contaminants in soil, posing potential health threats. This study aimed to examine the effects of applying a nitrogen fertilizer and a fungal agent Trichoderma harzianum J2 (nitrogen alone, fungi alone, and combined use) on the phytoremediation of soils co-contaminated with Pb and Cd. The growth of Leucaena leucocephala was monitored in the seedling, differentiation, and maturity stages to fully comprehend the remediation mechanisms. In the maturity stage, the biomass of L. leucocephala significantly increased by 18% and 29% under nitrogen-alone (NCK+) and fungal agent-alone treatments (J2), respectively, compared with the control in contaminated soil (CK+). The remediation factors of Pb and Cd with NCK+ treatment significantly increased by 50% and 125%, respectively, while those with J2 treatment increased by 73% and 145%, respectively. The partial least squares path model suggested that the nitrogen-related soil properties were prominent factors affecting phytoextraction compared with biotic factors (microbial diversity and plant growth). This model explained 2.56 of the variation in Cd concentration under J2 treatment, and 2.97 and 2.82 of the variation in Pb concentration under NCK+ and J2 treatments, respectively. The redundancy analysis showed that the samples under NCK+ and J2 treatments were clustered similarly in all growth stages. Also, Chytridiomycota, Mucoromucota, and Ciliophora were the key bioindicators for coping with heavy metals. Overall, a similar remediation mechanism allowed T. harzianum J2 to replace the nitrogen fertilizer to avoid secondary pollution. In addition, their combined use further increased the remediation efficiency.

Transcriptomic and physiological analysis provide new insight into seed shattering mechanism in Pennisetum alopecuroides 'Liqiu'

KEY MESSAGE

Through the histological, physiological, and transcriptome-level identification of the abscission zone of Pennisetum alopecuroides 'Liqiu', we explored the structure and the genes related to seed shattering, ultimately revealing the regulatory network of seed shattering in P. alopecuroides. Pennisetum alopecuroides is one of the most representative ornamental grass species of Pennisetum genus. It has unique inflorescence, elegant appearance, and strong stress tolerance. However, the shattering of seeds not only reduces the ornamental effect, but also hinders the seed production. In order to understand the potential mechanisms of seed shattering in P. alopecuroides, we conducted morphological, histological, physiological, and transcriptomic analyses on P. alopecuroides cv. 'Liqiu'. According to histological findings, the seed shattering of 'Liqiu' was determined by the abscission zone at the base of the pedicel. Correlation analysis showed that seed shattering was significantly correlated with cellulase, lignin, auxin, gibberellin, cytokinin and jasmonic acid. Through a combination of histological and physiological analyses, we observed the accumulation of cellulase and lignin during 'Liqiu' seed abscission. We used PacBio full-length transcriptome sequencing (SMRT) combined with next-generation sequencing (NGS) transcriptome technology to improve the transcriptome data of 'Liqiu'. Transcriptomics further identified many differential genes involved in cellulase, lignin and plant hormone-related pathways. This study will provide new insights into the research on the shattering mechanism of P. alopecuroides.

Exploration of the Effects of Cadmium Stress on Photosynthesis in Oenanthe javanica (Blume) DC

Cadmium ion (Cd2+) stress is a major abiotic stressor affecting plant photosynthesis. However, the impact of sustained high-concentration Cd stress on the photosynthetic electron transport chain of aquatic plants is currently unclear. Here, prompt fluorescence (PF), delayed fluorescence (DF), and P700 signals were simultaneously measured to investigate the effect of Cd stress on photosynthesis in water dropwort [Oenanthe javanica (Blume) DC.]. We aimed to elucidate how Cd stress continuously affects the electron transport chain in this species. The PF analysis showed that with prolonged Cd stress, the FJ, FI and FP steadily decreased, accompanied by a positive shift in the K-band and L-band. Moreover, JIP-test parameters, including TRO/ABS, ABS/CSO, TRO/CSO and PIABS, were significantly reduced. The P700 signals showed that exposure to Cd stress hindered both the fast decrease and slow increase phases of the MR transient, ultimately resulting in a gradual reduction in both VPSI and VPSII-PSI. The DF analysis showed a gradual decrease in the I1 and I2 values as the duration of stress from Cd increased. The above results suggested that Cd stress affected the photosynthetic electron transport in water dropwort by influencing the amount of active PSII and PSI, primarily affecting PSII RCs in the early to mid-stages and PSI reductive activity in the later stage.

Effect of EDDS on the rhizosphere ecology and microbial regulation of the Cd-Cr contaminated soil remediation using king grass combined with Piriformospora indica

The negative impacts of soil heavy metals composite pollution on agricultural production and human health are becoming increasingly prevalent. The applications of green chelating agents and microorganisms have emerged as promising alternate methods for enhancing phytoremediation. The regulatory effects of root secretion composition, microbial carbon source utilization, key gene expression, and soil microbial community structure were comprehensively analyzed through a combination of HPLC, Biolog EcoPlates, qPCR, and high-throughput screening techniques. The application of EDDS resulted in a favorable rhizosphere ecological environment for the king grass Piriformospora indica, characterized by a decrease in soil pH by 0.41 units, stimulation of succinic acid and fumaric acid secretion, and an increase in carbon source metabolic activity of amino acids and carbohydrates. Consequently, this improvement enhanced the bioavailability of Cd/Cr and increased the biomass of king grass by 25.7%. The expression of dissimilatory iron-reducing bacteria was significantly upregulated by 99.2%, while there was no significant difference in Clostridium abundance. Furthermore, the richness of the soil rhizosphere fungal community (Ascomycota: 45.8%, Rozellomycota: 16.7%) significantly increased to regulate the proportion of tolerant microbial dominant groups, promoting the improvement of Cd/Cr removal efficiency (Cd: 23.4%, Cr: 18.7%). These findings provide a theoretical basis for the sustainable development of chelating agent-assisted plants-microorganisms combined remediation of heavy metals in soil.

Piriformospora indica colonization enhances remediation of cadmium and chromium co-contaminated soils by king grass through plant growth promotion and rhizosphere microecological regulation

Poor plant growth and low pollutant bioavailability in contaminated soils limit phytoremediation efficiency. Pot experiments were conducted to investigate the effects and mechanisms of Piriformospora indica inoculation on the phytoremediation of Cd-Cr co-contaminated soils from farmland using king grass. P. indica colonization increased plant biomass by 20.4-24.6% and enhanced Cd/Cr accumulation in root, stem and leave tissues. Root vascular cylinder and cortex were the major structures for Cd/Cr transportation in plants. The amounts of Cd and Cr extracted by king grass considerably increased in the presence of P. indica (by 31.5-88.9% and 22.4-38.4%, respectively), as did the removal efficiency of both metals from soils (by 13.2-32.2% and 23.2-33.5%, respectively). Cd/Cr phytoextraction was closely related to the contents of alkanes, lipids and acids in root exudates. Following inoculation, the respiration of microbial sulfur compounds was promoted in soils at low and medium pollution levels, whereas nitrogen fixation and nitrification were reduced at high pollution level. This study demonstrates that P. indica inoculation enhances the phytoremediation efficiency of king grass for Cd-Cr co-contaminated soils through multiple regulation of plant growth, rhizosphere environment, root exudation and soil microbial function.

Differential physiological responses and tolerance to potentially toxic elements in Primula forbesii Franch

Environmental pollution caused by potentially toxic elements (PTEs) has become a global problem that endangers environmental sustainability due to industrial, agricultural, and urban pollution. Primula forbesii Franch. (a synonym of Primula filipes G. Watt.) is a biennial flower native to China with excellent stress resistance and ornamental value. In this study, we examined the phenotypic traits, growth indexes, and physiological properties of P. forbesii in response to five representative PTEs (Cd, Ni, Cr(III), Cu, and Zn) under hydroponic culture conditions. High concentrations of Zn and Cr had little effect on the growth and physiological properties of P. forbesii, indicating that the species has strong tolerance to Zn and Cr stress. Alternatively, high concentrations of Cd, Ni, and Cu seriously affected plant growth and development, resulting in leaf chlorosis and even death, and therefore may have a serious negative impact on the growth of P. forbesii. However, activity levels of some antioxidant enzymes and osmotic regulatory substances remained high, indicating that P. forbesii resisted PTE stress by regulating physiological and biochemical metabolism to a certain extent. Furthermore, principal component analysis and membership function were used to comprehensively evaluate P. forbesii resistance to PTEs. These analyses revealed that P. forbesii exhibits distinct sensitivities and physiological responses to different PTEs and suggested that the resistance to five PTEs in decreasing order is Zn > Cr > Cd > Cu > Ni. These results provide a theoretical basis for the future application of P. forbesii in environments with PTE pollution and may expand its practical utilization.

Ca alleviated Cd-induced toxicity in Salix matsudana by affecting Cd absorption, translocation, subcellular distribution, and chemical forms

Cadmium (Cd), a ubiquitous and highly toxic heavy metal pollutant, is toxic to animals and plants. Calcium (Ca) is an essential component for plant growth and reduces plant Cd absorption by competing with Cd. To gain deeper insight into the effects of Ca on Cd absorption, translocation, subcellular distribution, and chemical forms in S. matsudana seedlings under Cd stress, an investigation was conducted on these properties. Adding Ca alleviated Cd physiological toxicity in S. matsudana, reduced Cd absorption, increased the translocation from roots to shoots, lead to subcellular redistribution of Cd by increasing the proportion of Cd in soluble fractions but decreasing Cd in the cell wall and changed the chemical forms of Cd from 0.6 mol/L HCl- and 2% HAc-extracted Cd to 1 mol/L NaCl-extracted Cd. The energy dispersive X-ray analyses (EDXA) results revealed that after adding Ca, Cd was transferred through the root epidermis, cortex, endodermis, and vascular cylinder, transported to the shoots, and was highly accumulated in leaf epidermal and mesophyll cells, but less in leaf vein and guard cells. The genes involved in Cd uptake and xylem loading included NRAMP1, ZIP8, HMA2, and HMA4, which were up-regulated significantly (P < 0.05) in the Cd and Cd + Ca treatments compared to the control. The findings of this study provide new insight into the mechanism that Ca alleviates Cd toxicity in woody tree species, as well as propose an important prospect of Ca addition for improving the phytoremediation of Cd contamination.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg^-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg^-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Phytoextraction by Moso Bamboo under high level chromium stress in mediterranean conditions

In this study a bamboo species, Moso Bamboo (MB) - Phyllostachys pubescens - has been selected for its heavy metal accumulation capacity and translocation potential to restore Cr-contaminated soil. Experiments have been conducted so to evaluate the capability of MB to remove Cr from soil, growing under Mediterranean conditions, irrigated with water containing 180 mgCr/L, at flow rate of 600 mm/year. The soil has been contaminated by the irrigation water. When the concentration of Cr in soil reached 300 mgCr/kg, Cr phytoextraction by MB from soil at the same irrigation rate of 600 mm/year with uncontaminated water has been evaluated. Cr removal from soil was approx. 42% after 6 weeks and 60.7% after 12 weeks, starting from a Cr content in soil of approximately 300 mg/kg. MB growing in Cr contaminated soil has shown Cr concentration per gram of dry biomass in aerial parts greater than the underground parts of the plants. After 12 weeks of cultivation, the quantity of Cr in roots and rhizome was measured as 1.79 mg/g, while in stems and leaves as 2.49 mg/g. Results shown a bioconcentration factor of 0.77, 0.65, 0.18, 0.08, after 6 weeks and 0.64, 0.98, 0.53, 0.26 after 12 weeks for roots, rhizomes, stems and leaves, respectively and a translocation factor equal to 0.23 and 0.11 after 6 weeks and 0.83 and 0.40 after 12 weeks, for stems and leaves, respectively.

Phytoremediation potential of Bermuda grass (Cynodon dactylon (L.) pers.) in soils co-contaminated with polycyclic aromatic hydrocarbons and cadmium

Soils co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and cadmium (Cd) have serious environmental impacts and are highly toxic to humans and ecosystems. Phytoremediation is an effective biotechnology for the remediation and restoration of PAH- and Cd-polluted soils. Pot experiments were conducted to investigate the individual and combined effects of PAHs (1238.62 mg kg-1) and Cd (23.1 mg kg-1) on the phytoremediation potential of Bermuda grass grown in contaminated soils. Bermuda grass exhibited a significant decrease in plant growth rate, leaf pigment content, root activity, plant height and biomass and a remarkable increase in malondialdehyde content and electrolyte leakage when grown in PAH- and Cd-contaminated soils compared with grass grown in uncontaminated soils. The activity of soil enzymes, including urease, alkaline phosphatase, sucrose, and fluorescein diacetate hydrolysis, were reduced in soil with PAH and Cd stress. Furthermore, the toxicity of combined PAHs and Cd on Bermuda grass growth and soil enzyme activity was much higher than that of PAH or Cd stress alone, suggesting a synergistic effect of PAHs and Cd on cytotoxicity. To scavenge redundant reactive oxygen species and avoid oxidative damage, Bermuda grass increased plant catalase, superoxide dismutase, and peroxidase activity and soluble sugar and proline content. The bioconcentration factor of Cd in Bermuda grass grown under Cd alone and combined PAH and Cd exposure was greater than 1 for both, suggesting that Bermuda grass has a high Cd accumulation ability. Under PAH alone and combined PAH and Cd exposure conditions, a higher PAH removal rate (41.5-56.8%) was observed in soils planted with Bermuda grass than in unplanted soils (24.8-29.8%), indicating that Bermuda grass has a great ability to degrade PAHs. Bermuda grass showed great phytoremediation potential for the degradation of PAHs and phytoextraction of Cd in co-contaminated soils.

Influence of nitrogen forms, pH, and water levels on cadmium speciation and characteristics of cadmium uptake by rapeseed

Rapeseed (Brassica napus L.) is an ideal crop for remediation in cadmium (Cd)-contaminated soil in farmland. The main objective of this study was focused on the combined effects of four nitrogen forms (urea, ammonium nitrogen, nitrate nitrogen, ammonium nitrate fertilizer), four pH levels (5, 6, 7, 8), and three water levels (low water, middle water, high water) on Cd speciation and characteristics of Cd uptake by rapeseed. A pot experiment was conducted at the Xindu Experimental Park in Sichuan Province, China. Experimental results indicated that the interaction effects of pH and nitrogen forms, three factors on Cd speciation (except organic-bound Cd and exchangeable Cd), were significant and the interaction effects of pH and nitrogen forms on Cd uptake by rapeseed also was significant only under the condition of planting rapeseed. The higher the water level was or the lower the pH value was, the better the repair effect rapeseed to Cd was. High water significantly increased the stem Cd content by 11.89% and 29.55% through significantly increasing the content of exchangeable Cd by 23.40% and 52.63%, respectively, compared with middle water and low water as planting rapeseed, and pH 5 significantly increased the stem Cd content, total Cd enrichment coefficients, bio-availability coefficient, and Cd removal rate by 24.45~40.33%, 49.45~76.62%, 60.00~166.67%, and 16.67~26.00%, respectively, through significantly increasing the content of exchangeable Cd by 37.78~113.79%, compared with pH 7 and pH 8 as the significant decreasing of carbonate-bound Cd, bound to Fe-Mn oxide, and content of organic-bound Cd and residual Cd. Ammonium nitrate also significantly increased total Cd enrichment coefficients, bio-availability coefficient, and Cd removal rate by 45.63~138.10%, 21.05~109.09%, and 40.00~77.50%, respectively, compared with other three nitrogen forms as good growth and Cd resistance of rapeseed. Path analysis structural equation modeling revealed that content of exchangeable Cd and residual Cd had significant and direct path coefficients with variances in stem Cd content of rapeseed. Combined with the safety of edible oil, the best management practices for optimal remediation efficiency of rapeseed to Cd-contaminated soil were ammonium nitrate fertilizer, pH = 5, and high water.

Remediation of soils co-contaminated with cadmium and dichlorodiphenyltrichloroethanes by king grass associated with Piriformospora indica: Insights into the regulation of root excretion and reshaping of rhizosphere microbial community structure

Cadmium (Cd) and dichlorodiphenyltrichloroethane (DDT) are frequently detected in agricultural soils, which poses a threat to public health. This study investigated the effects of inoculation of king grass with Piriformospora indica on the remediation of soils co-contaminated with Cd and DDTs. After treatment for 90 days, the dry shoot and root biomass of king grass inoculated with P. indica markedly increased by 13.0-15.8% and 24.1-46.4%, respectively, compared with those of uninoculated plants. Inoculation with P. indica also increased the uptake of Cd and DDTs by shoots and roots of king grass. The removal efficiency of Cd and DDTs from soils reached 4.88-17.4% and 48.4-51.0%, respectively, in the presence of king grass inoculated with P. indica. Under three Cd-DDTs contamination conditions, root secretion of organic acids, alcohol, and polyamines was distinctively stimulated by P. indica inoculation of king grass compared with planting king grass alone. After phytoremediation, changes in soil bacterial and fungal community composition occurred at different contamination levels. Overall, the results showed that king grass associated with P. indica can be adopted for phytoextraction of Cd and DDTs from moderately contaminated soils by regulating root excretion and reshaping rhizosphere microbial community structure.

Morpho-physiological growth performance and phytoremediation capabilities of selected xerophyte grass species toward Cr and Pb stress

Being sessile organisms, plants cannot escape unwanted changes in the environment. The rapid human population explosion caused significant environmental problems. Heavy metals produced through various sources can cause severe damage to living organisms. The study was planned to evaluate four grass species' morpho-physiological growth characteristics and phytoremediation capabilities under chromium (Cr) and lead stress (Pb) in the arid climate. Typha angustifolia, Tragus roxburghii, Aeluropus logopoides, and Cenchrus ciliaris grass species were used for the study. One-year-old stubbles from the Cholistan desert were used for the experiment. Cr treatments in the form of K₂Cr₂O₇ were applied at 0, 20, 40, and 80 mg L^-1, whereas Pb was applied as PbCl₂ at 0, 50, 200, and 500 mg L^-1 as control, low, moderate and high-stress, respectively. After 6 weeks of heavy metals treatments, plants were harvested and analyzed for growth performance and phytoremediation capabilities. Results depicted that, regarding morphological attributes, T. angustifolia performed better, followed by C. ciliaris; no clear pattern was observed for T. roxburghii and A. logopoides. The CO₂ assimilation rate (Co₂d) and water use efficiency (WUE) increased as the heavy metal stress increased in all species under both metals. In contrast, total chlorophyll content was higher under low stress. Other physiological parameters, such as relative humidity (RHd), net photosynthetic rate (A), transpiration rate (E), stomatal conductance (Gs), leaf internal CO2 concentration (Ci) and membrane stability index (MSI) gradually decreased as the Cr, and Pb stress levels increased among all the species. Moreover, Cr and Pb absorption contents of T. angustifolia were higher than the other three species at each stress level. Overall, T. angustifolia thrived against heavy metals stress and showed higher biomass, maximum photosynthetic measurements, WUE and higher metal absorption among all the selected species. Results concluded that although all the selected species behaved fine under stress conditions, T. angustifolia performance was better; thus, it can be used to remediate the soil near industrial estates.

Potassium reduces oxidative stress in tanzania guinea grass under cadmium toxicity

Plants used for phytoextraction of metals need to tolerate toxicity conditions. Potassium (K) participates in physiological and biochemical processes that can alleviate toxicity by heavy metals, including cadmium (Cd). This study aimed to evaluate the effect of K on photosynthesis and on the changes in the antioxidant system of tanzania guinea grass [Panicum maximum Jacq. cv. Tanzania (syn. Megathyrsus maximus (Jacq,) B.K. Simon & S.W.L. Jacobs)] under Cd toxicity. Plants were grown in a greenhouse, in nutrient solution, in a randomized complete block design, arranged in a 3 × 4 factorial, with three replications. Plants were supplied with three K levels (0.4 [K deficiency], 6.0, and 11.6 mmol L^-1) and exposed to four Cd levels (0.0, 0.5, 1.0, and 1.5 mmol L^-1). Two plant growth periods were evaluated. High Cd level (1.5 mmol L^-1) led to a reduction in net photosynthesis (76%) by causing low stomatal conductance and losses in quantum efficiency of photosystem II. However, high K supply (11.6 mmol L^-1) increased the net photosynthesis by 15% in plants exposed to 1.0 mmol L^-1 Cd, due to upregulation of proline synthesis. Cd toxicity resulted in increases in lipid peroxidation and hydrogen peroxide concentration (35 and 50%; 25 and 30%, at first and second harvest, respectively) and reduction by 80-100% in activity of the antioxidant enzymes: superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase in the shoots of the grass. However, the high K supply (11.6 mmol L^-1) increased the activity of these enzymes (about 50-75%) and reduced lipid peroxidation (36%), restoring cellular homeostasis. Moreover, high K supply promoted a 25% increase in spermidine and spermine concentrations in the shoots. Therefore, K reduced the Cd-induced oxidative stress and increased the net photosynthesis in tanzania guinea grass by increasing the activity of antioxidant enzymes and proline and polyamines synthesis, which enhances the tolerance of this grass to Cd.

The intercropping and arbuscular mycorrhizal fungus decrease Cd accumulation in upland rice and improve phytoremediation of Cd-contaminated soil by Sphagneticola calendulacea (L.) Pruski

Little is known about the impact of the combined application of intercropping and arbuscular mycorrhizal fungus (AMF) on the plant growth and Cd accumulation in the two intercropped plants. A greenhouse pot experiment was performed to investigate the effects of intercropping (IC) and AMF-Glomus versiforme (GV) on the growth, photosynthesis, Cd accumulation and antioxidant activities in the two intercropped plants-upland rice and Cd hyperaccumulator Sphagneticola calendulacea (L.) Pruski in the soils added with 5 mg Cd kg^-1. It was found that the GV inoculation and the combined treatment of IC and GV (IC + GV) significantly (p < 0.05) increased the biomasses and the P contents of upland rice and S. calendulacea. In addition, the Cd concentrations and uptakes of plants in IC, GV and IC + GV treatments were significantly (p < 0.05) dropped in upland rice but increased in S. calendulacea compared with the monocropping control, and the compound treatment showed better effect on decreasing Cd accumulation in upland rice (especially grains) and increasing Cd uptake by S. calendulacea compared with the single intercropping or AMF treatment. Moreover, IC, GV and IC + GV treatments significantly (p < 0.05) improved the net photosynthetic rate, stomatal conductance and transpiration rate of the two intercropped plants. Finally, IC, GV and IC + GV treatments all significantly increased the catalase activities and total antioxidant capacities, while decreased the malondialdehyde contents in upland rice and S. calendulacea. The present work could provide a feasible strategy for safe production of upland rice and phytoremediation of Cd contaminated soils.

Irrigating digestate to improve cadmium phytoremediation potential of Pennisetum hybridum

The bioavailability of heavy metal and growth of hyperaccumulator are key factors controlling the phytoextraction of heavy metal from soil. In this study, the efficacy and potential microbial mechanisms of digestate application in enhancing Cd extraction from soil by Pennisetum hybridum were investigated. The results showed that digestate application significantly promoted the height, tiller number, and biomass yield of Pennisetum hybridum. The application also increased the activities of urease, sucrase, dehydrogenase, available Cd contents of rhizosphere soils (from 2.21 to 2.46 mg kg^-1), and the transfer factors of Cd from root to shoot and leaf. Assuming three annual harvests, digestate application would substantially reduce time needed for Pennisetum hybridum to completely absorb Cd from soil-from 15-16 yr-10 yr. Furthermore, the results of microbial community diversity analysis showed that digestate irrigation was more facilitated for the growth of the predominant bacteria, which were Actinobacteria and Chloroflexi at phylum level, and Sphingomonas and Nitrospiraat genus level, which mainly have the functions of promoted plant growth and metal resistance. The results suggested that the enhanced phytoextraction of Cd by Pennisetum hybridum with digestate application might mainly attributed to the increased Cd bio-availability and the enhanced plant growth, indicating that an approach combining digestate and Pennisetum hybridum could be a promising strategy for remediating Cd-contaminated soils.

Overexpression of SmZIP plays important roles in Cd accumulation and translocation, subcellular distribution, and chemical forms in transgenic tobacco under Cd stress

Plant ZIP genes represent an important transporter family and may be involved in cadmium (Cd) accumulation and Cd resistance. In order to explore the function of SmZIP isolated from Salix matsudana, the roles of SmZIP in Cd tolerance, uptake, translocation, and distribution were determined in the present investigation. The transgenic SmZIP tobacco was found to respond to external Cd stress differently from WT tobacco by exhibiting a higher growth rate and more vigorous phenotype. The overexpression of SmZIP in tobacco resulted in the reduction of Cd stress-induced phytotoxic effects. Compared to WT tobacco, the Cd content of the root, stem, and leaf in the transgenic tobacco increased, and the zinc, iron, copper, and manganese contents also increased. The assimilation factor, translocation factor and bioconcentration factor of Cd were improved. The scanning electron microscopy and energy dispersive X-ray analysis results of the root maturation zone exposed to Cd for 24 h showed that Cd was transferred through the root epidermis, cortex, and vascular cylinder and migrated to the aboveground parts via the vascular cylinder, resulting in the transgenic tobacco accumulating more Cd than the WT plants. Based on the transverse section of the leaf main vein and leaf blade, Cd was transported through the vascular tissues to the leaves and accumulated more greatly in the leaf epidermis, but less in the leaf mesophyll cells, following the overexpression of SmZIP to reduce the photosynthetic toxicity. The overexpression of SmZIP resulted in the redistribution of Cd at the subcellular level, a decrease in the percentage of Cd in the cell wall, and an increase of the Cd in the soluble fraction in both the roots and leaves. It also changed the percentage composition of different Cd chemical forms by elevating the proportion of Cd extracted using 2% HAc and 0.6 mol/L HCl, but lowering that of the Cd extracted using 1 mol/L NaCl in both the leaves and roots under 10 and 100 μmol/L Cd stress for 28 d. The results implied that SmZIP played important roles in advancing Cd uptake, accumulation, and translocation, as well as in enhancing Cd resistance by altering the Cd subcellular distribution and chemical forms in the transgenic tobacco. The study will be useful for future phytoremediation applications to clean up Cd-contaminated soil.

Potential use of king grass (Pennisetum purpureum Schumach. × Pennisetum glaucum (L.) R.Br.) for phytoextraction of cadmium from fields

Using king grass (Pennisetum purpureum Schumach. × Pennisetum glaucum (L.) R.Br.) for phytoextraction is a promising technology for producing large amounts of biomass fuel while remediating contaminated soil. To assess the practical phytoextraction capacity of king grass, we conducted a field experiment with three different soil types (loam, sandy loam, clay loam) and cadmium (Cd) concentrations (0, 0.25, 0.5, 1, 2, 4, 8, and 16 mg kg^-1, aged stably for 6 years). King grass were harvested at two different periods (elongation and maturity) to identify the optimal harvest time for extraction efficiency. The results showed that all treatments had bioconcentration factor (BCF) > 1 and translocation factor (TF) < 1; Cd is mainly stored in the roots. However, due to a high shoot biomass, the highest quantity of Cd extracted from shoots was 2.75 mg plant^-1, from the experimental group with 16 mg kg^-1 Cd added in sandy loam. A significant positive relationship (P < 0.05) was observed between the amount of Cd extracted from king grass stems, leaves, and roots from soil with the diethylene triamine pentacetate acid (DTPA) extractable Cd concentration. The Cd concentration in shoots at the maturity stage is lower than at the elongation stage, mainly due to the effect of biological dilution. Meanwhile, there is significantly more biomass (P < 0.05) at the maturity stage than at the elongation stage. At the latter, the extraction efficiency of the three soils was loam > sandy loam > clay loam, while at maturity it was sandy loam > clay loam > loam. This change in extraction efficiency can be attributed mainly to differences in soil DTPA-extractable Cd concentration and growth rate caused by differences in soil physical and chemical properties. According to calculations from multiple harvests using three types of soil, remediating contaminated soil with 0-16 mg kg^-1 Cd would take 13.9-224.5 and 19.5-250.6 years, extracting 7.21-265.23 and 4.96-330.52 g ha^-1 Cd while producing 33.62-66.50 and 73.8-110.5 t ha^-1 dry biomass at the elongation (90 days) and maturity (120 days) stages, respectively. In summary, king grass has major potential for remediating Cd-contaminated soil while producing large volumes of biofuel.

Phytoremediation capacity, growth and physiological responses of Crambe abyssinica Hochst on soil contaminated with Cd and Pb

The search for vegetal species regarding effectiveness in the phytoremediation of soils is of great importance, mainly in function of the great environmental problems, such as soil contamination with heavy metals, the necessity of producing more food, among others that mankind face today. This work aimed (i) to evaluate phytoremediation capacity of Crambe abyssinica Hochst and its growth in soil artificially contaminated with Cd and Pb, and (ii) to evaluate the possible impacts of crambe cultivation in contaminated soil conditions, in order to evaluate, to test, and to question the Brazilian CONAMA 420, providing important information that can be useful for governmental and environmental purposes. Two simultaneous experiments were developed, one for each metal. The soils were contaminated with salts of CdCl₂ and PbCl₂H₂O in five doses based on the investigation values (IV) of CONAMA Resolution 420, resulting in 0; 1.5; 3; 9 and 30 mg kg^-1 for Cd and 33; 90; 180; 540 and 1800 mg kg^-1 for Pb. Gaseous exchange, development, nutritional composition and production of plant components, as well as phytoavailability of metals, were evaluated. The contamination with metals reduced photosynthesis, increased breathing as well as leading to a negative effect on the mineral nutrition and productivity in general; Plants cultivated in soil with Cd presented higher phytoavailability when compared to those cultivated in the Pb conditions, being found metals in all parts of the crambe plants from 1.5 mg kg^{- 1} of Cd in the soil; and Pb was retained only in roots, not being translocated in the plant. Cd showed higher phytoavailability, being found in all parts of the plant and Pb was retained only in the roots. Cd showed a higher phytoavailability when compared to Pb, also being found in all parts of crambe plants from dose 1.5 mg kg-1 of Cd in soil, which is an environmental problem, since in these concentrations the cultivation of crops is allowed by Brazilian legislation CONAMA 420.

Bamboo - An untapped plant resource for the phytoremediation of heavy metal contaminated soils

Phytoremediation is a green technology used for the remediation of heavy metal soils. However, up to now, very few plants are known to be both hyperaccumulators and fast-growers. In contrast, some non-hyperaccumulators, which possess lower extraction capacities than hyperaccumulators, are fast-growing species with much higher total biomass yields and are potential alternative phytoremediators. Bamboo is a taxonomic group comprised of 1439 species that are mostly distributed in the tropics and subtropics. Although limited studies on bamboo for phytoremediation, recent studies have shown that some bamboo species have high ability to adapt to metalliferous environments and a high capacity to absorb heavy metals. Bamboo tissues in the rhizome and culm can accumulate a large amount of heavy metals that mainly accumulate in the cell wall, vacuole, and cytoplasm. Certain bamboo species such as moso bamboo, Phyllostachys praecox, have been shown to have a high endurance in metal contaminated soils, enabling a considerable uptake and accumulation of heavy metals. However, excessive concentrations of heavy metals may cause oxidative stress and damage bamboo plants. Therefore, several management strategies have been developed to improve the phytoremediation ability of bamboo species, including the selection of tolerant bamboo species, intercropping with hyperaccumulators, fertilization applications, and employment of chelate in soil. This review demonstrates that bamboo species, which have high biomass productivity, short rotation, and high economic value, can be used for phytoremediation. However, the mechanisms of heavy metal uptake, transport, sequestration, and detoxification of different bamboo species require urgent investigation.

Effects of amendments and aided phytostabilization of an energy crop on the metal availability and leaching in mine tailings using a pot test

A complete orthogonal experiment using a pot test is conducted to investigate the effects of four amendments (biochar, peat, manure, and non-contaminated soil (NCS)) on the metal availability, mobility, and phytostabilization potential of an energy crop, king grass (Pennisetum purpureum × P. thyphoideum), in Pb/Zn mine tailings. The addition of amendments significantly increased the pH and fertility of the tailings, while significantly decreasing the heavy metal available contents in the tailings. The available Cd, Pb, Zn, and As concentrations in the tailings in the treatment amended with biochar+NCS+peat+manure were 51.00%, 36.62%, 50.57%, and 75.88%, respectively, lower than those in the treatment control. The king grass survived in the tailings without amendments, while amendments made the plant grow well or better in the tailings than in NCS. The addition of amendments significantly reduced the content of heavy metals and bioaccumulation factor (BCF) in the plant root but increased the translocation factor (TF) of Cd, Zn, and As and had little effect on the TF of Pb. The TF for heavy metals in plant were lower than one for all of the treatments. During a leaching period of 30 days, the pH of the leachate declined slowly and then maintained at 6.0~6.6. The addition of the amendments significantly reduced the metal concentrations of the leachates, and the highest declines were 50.46%, 20.04%, 41.58%, and 47.04% for Cd, Pb, Zn, and As, respectively. Biochar had a higher immobilization capacity for Cd, Pb, Zn, and As than manure, peat, and NCS. King grass could be used to aid phytostabilization for Cd- and Pb-polluted tailings, and biochar-rich amendments were effective for the in situ immobilization of metals. Further field monitoring is necessary to demonstrate the effectiveness of king grass and amendments under the climatic conditions of China.

Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Biochar alleviates Cd phytotoxicity by minimizing bioavailability and oxidative stress in pak choi (Brassica chinensis L.) cultivated in Cd-polluted soil

The production of leafy vegetables such as Brassica chinensis L. in cadmium (Cd)-polluted soil causes serious threats to human health and food safety around the globe. A pot culture was established to examine the efficacy of rice-straw induced biochar (applied to soil at the rate of 0%, 2.5% and 5%, w/w) on growth, gaseous exchange attributes, antioxidative capacities and Cd uptake in pak choi (Brassica chinensis L.), when soil was spiked with Cd (CdCl₂) at 0, 5, 10 and 20 mg kg^-1 soil. The results revealed that Cd stress significantly (P < 0.05) reduced plant biomass and physiological attributes, and accumulated higher Cd concentrations in plant tissues with the increasing rate of Cd concentration in the soil. However, incorporation of biochar at 5% application rate prominently increased the shoot (98.27%) and root (85.96%) dry biomass, net photosynthesis (45.52%), transpiration rate (161.34%), stomatal activity (111.76%) and intracellular CO₂ concentration (32.25%) when Cd was added at 20 mg kg^-1 soil, relative to the respective treatment without biochar. Whereas, incorporation of biochar at 5% significantly reduced the bioavailable Cd by 16.64% under 20 mg kg^-1 soil, compared to respective Cd treatment without biochar.Similarly, Cd accumulation in shoots and roots was decreased by 42.49% and 29.23%, and thereby reduced leaf MDA and H₂O₂ contents by 21.45% and 31.28%, respectively, at 20 mg Cd kg^-1 spiked soil relative to without biochar amended soil. An increment was noticed in the activities of guaiacol peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione (GSH) by 37.31%, 66.35%, 115.94%, 122.72% and 59.96%, respectively, with 5% biochar addition in 20 mg kg^-1 Cd spiked soil. Moreover, biochar induced a synergistic impact on plants by increasing soil alkalinization and thereby reducing Cd phytotoxicity throughimmobilization. Overall, results proposed that rice-straw biochar has an ability to restore Cd polluted soil and increased pak choi production and thereby reduced food security risks in polluted soil.

The Effects of Rainfall Runoff Pollutants on Plant Physiology in a Bioretention System Based on Pilot Experiments

Bioretention facilities have been widely used in the construction of Sponge City in China, but there have also been doubts about whether road runoff pollutants have adverse effects on plant growth. In response to this problem, this paper explored the effects of bioretention on the removal of pollutants and explored the effects of runoff on plant growth and physiology. The results showed that (1) the average concentration reduction rate and load removal rate of TN and NO3--N were above 70%, the average NH4+-N concentration reduction rate and load removal rate were greater than 90%, and the removal of elemental N was affected by the influent concentration. The removal effect of the four heavy metals was not very great. The average concentration reduction rate and load removal rate of heavy metals were 65.4–95.7% and 85.4–99.4%, respectively. The cumulative load removal rate of various pollutants was above 87.0%. (2) The runoff of high–concentration pollutants had a negative or no significant effects on the net photosynthesis rates (Pn), chlorophyll contents (CC), and electrolyte leakage (EL) of most plants (e.g., Iris tectorum Maxim, Rosa xanthina Lindl, and Ligustrum vicaryi). It had a significantly negative effect on the plant height of shrub plants (e.g., Rosa xanthina Lindl and Ligustrum vicaryi), but had a positive effect on Pn and CC of Iris lactea var. chinensis. (3) The runoff of low–concentration pollutants had a positive or no significant effects on the physiological indexes of herbaceous plants (e.g., Iris tectorum Maxim and Iris lactea var. chinensis), but there were no explicit conclusions regarding the physiological indicators of shrub plants (e.g., Rosa xanthina Lindl and Ligustrum vicaryi). It had no obvious effects on the plant height of these four species of plants.

Phytoremediation of Cd and Pb interactive polluted soils by switchgrass (Panicum virgatum L.)

Using phytoremediation as an efficient technique to remove heavy metals from contaminated soils is a current research hotspot. This study used an orthogonal matrix experimental design with three factors (Cd, Pb, and pH) and five levels (Cd at 9.45, 30, 60, 90, and 110.46 µg/g; Pb at 195.4, 400, 700, 1000, and 1204.6 µg/g; and pH at 3, 4.1, 5.8, 7.5, and 8.6) to investigate the phytoremediation potential of Panicum virgatum L. for soils polluted with cadmium (Cd) and lead (Pb). The results indicated that there was a significant decrease in belowground biomass in plants exposed to the stresses compared to the control. Superoxide dismutase (SOD) activity, peroxidase (POD) activity, and malondialdehyde (MDA) content were affected. Interaction of Cd with Pb in the soil had an antagonistic effect on the Cd bioaccumulation factor, whereas the interaction of pH with Cd or Pb had synergistic effects on the Cd bioaccumulation factor. When exposed to the three stressors, switchgrass plants could grow in soil that had a Cd concentration of a 46.68 µg/g, Pb concentration of 568.75 µg/g and pH of 5.34, which is a mildly acidic condition. Switchgrass, used as a phytoremediation plant, was more efficient in Cd-contaminated than in Pb-contaminated soil.

Detection of Cadmium Risk to the Photosynthetic Performance of Hybrid Pennisetum

Photosynthesis plays an essential role in plant growth and crop yield, and the mechanisms of the effects of cadmium (Cd) on photosynthetic performance require more attention. The acute toxicity of Cd in soil to the photosynthetic capacity of Hybrid Pennisetum was evaluated using gas exchange parameters, A/Ci curves, light response curves, and chlorophyll a fluorescence transients after exposure to elevated Cd concentrations (0, 10, 20, 50, 70, and 100 mg kg-1) for a 3-month period. The results indicated that leaf Cd concentration in Hybrid Pennisetum increased with the strength of soil Cd stress and ranged from 4.9 to 15.8 μg g-1 DW. The accumulation of leaf Cd severely restricted photosynthesis and its non-stomatal limitation in regulating the photosynthetic performance of Hybrid Pennisetum. The leaf chloroplasts at 10 and 20 mg kg-1 Cd concentrations showed no noticeable change, but the chlorophyll content significantly decreased by 9.0-20.4% at 50-100 mg kg-1 Cd concentrations. The Cd treatments also decreased plant ribulose-1,5-bisphosphate (RuBP) activity (Vcmax ) and regeneration capacity (Jmax ), triose phosphate utilization (TPU), light-saturated photosynthesis (Amax ), apparent quantum yield (AQY), light saturation point (LSP), and dark respiration (Rday ), but Cd treatment increased the light compensation point (LCP). The shape of chlorophyll a fluorescence transients in leaves was altered under different Cd treatments. The increased OJ phase and the decreased IP phase in fluorescence induction curves suggested that Cd toxicity inhibited both light use efficiency and photodamage avoidance ability. These results suggested that the decrease in photosynthesis through exposure to Cd may be a result of the decrease in leaf chlorophyll content, Rubisco activity, and RuBP regeneration, inhibition of triose phosphate utilization, reduction of the ability to use light and provide energy, and restrictions on electron transport in PSII.

Transcriptome Analysis to Shed Light on the Molecular Mechanisms of Early Responses to Cadmium in Roots and Leaves of King Grass (Pennisetum americanum × P. purpureum)

King grass, a hybrid grass between pearl millet and elephant grass, has many excellent characteristics such as high biomass yield, great stress tolerance, and enormous economic and ecological value, which makes it ideal for development of phytoremediation. At present, the physiological and molecular response of king grass to cadmium (Cd) stress is poorly understood. Transcriptome analysis of early response (3 h and 24 h) of king grass leaves and roots to high level Cd (100 µM) has been investigated and has shed light on the molecular mechanism underlying Cd stress response in this hybrid grass. Our comparative transcriptome analysis demonstrated that in combat with Cd stress, king grass roots have activated the glutathione metabolism pathway by up-regulating glutathione S-transferases (GSTs) which are a multifunctional family of phase II enzymes that detoxify a variety of environmental chemicals, reactive intermediates, and secondary products of oxidative damages. In roots, early inductions of phenylpropanoid biosynthesis and phenylalanine metabolism pathways were observed to be enriched in differentially expressed genes (DEGs). Meanwhile, oxidoreductase activities were significantly enriched in the first 3 h to bestow the plant cells with resistance to oxidative stress. We also found that transporter activities and jasmonic acid (JA)-signaling might be activated by Cd in king grass. Our study provided the first-hand information on genome-wide transcriptome profiling of king grass and novel insights on phytoremediation.

Silicon Amendment Reduces Soil Cd Availability and Cd Uptake of Two Pennisetum Species

Silicon (Si) plays important roles in alleviating heavy metal stress, but the migrating effects and mechanisms, especially for Pennisetum, are not well studied. In this study, Pennisetum glaucum and Pennisetum glaucum × P. purpureum were used to explore the impacts of Si application on alleviating cadmium (Cd) toxicity and its possible mechanism. Treatments consist of four levels of Cd (0, 10, 50, and 100 mg·kg⁻¹) with or without 2.0 mM Si amendments. Under Cd stress, Si application significantly increased plant biomass and Si content, reduced Cd content, and decreased the enrichment factor in shoots and roots. Si treatment also increased soil pH and soil residual Cd, while reducing available/oxidizable/reducible Cd content in soil at 50 and 100 mg·kg⁻¹ Cd levels, thereby leading to a reduction of the soil’s available Cd. These findings indicate that Si application is effective in alleviating Cd phytotoxicity of Pennisetum, mainly through reducing plant Cd uptake and increasing soil pH and Cd immobilization, thereby reducing Cd bioavailability.

Enhanced uptake of Cd by biofilm forming Cd resistant plant growth promoting bacteria bioaugmented to the rhizosphere of Vetiveria zizanioides

Heavy metals are the major cause of pollution and cadmium is one among the highly toxic metals discharged into the environment from various industries. The current study was focused on the bioremoval of cadmium by phyto and rhizoremediation approach using Vetiveria zizanioides. The bacterial strains were isolated from wetland paddy rhizosphere soil and the isolate VITJAN13 was found to be a biofilm forming Cd resistant plant growth promoting rhizobacteria (PGPR). The 16S rRNA gene sequencing revealed VITJAN13 to be the closest neighbor of Aeromonas sp. and was submitted to Genbank with the accession number KX770741. Further, pot culture studies indicated that the treatments bioaugmented with VITJAN13 increased the root length and shoot height by 21.4 and 17.36%, respectively as compared to the non-augmented plants. Hence, bioaugmentation of Aeromonas sp. in the rhizosphere of Vetiveria zizanioides enhanced the uptake of cadmium by 67.7% in the soil treated with 15 mg/kg of Cd to that of the phytoremediation setup.

Metabolite profiling and molecular responses in a drought-tolerant savory, Satureja rechingeri exposed to water deficit

This study aimed to determine the response of Satureja rechingeri to water deficit by quantifying the expression of three targeted genes and four traditional reference genes using quantitative real-time PCR analysis (RT-qPCR). Drought stress was imposed by withholding water 4 months after planting. Profiling of volatile and non-volatile compounds using gas chromatography/mass spectrometry (GC/MS) and high-performance thin layer chromatography (HPTLC) showed an increasing-decreasing trend of major phenolic and terpenoid compounds such as rosmarinic and caffeic acids, carvacrole, thymol and p-Cymene. Drought stress also lead to significant increases in oil yield, soluble sugars and proline as well as significant reductions in leaf water potential (LWP), relative water content (RWC), and pigments. Metabolite profiling revealed the strategies savory employed to generate different biochemical phenotypes. RT-qPCR analysis showed that up-regulation of the three genes [1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR), 3-hydroxy-3-methylglutaryl-coenzyme. A reductase (HMGR) and rosmarinic acid synthase: 4-coumaroyl-CoA (RAS)] selected from the phenylpropanoid and terpenoid biosynthesis pathways were markedly enhanced at the transcript levels of the regulatory steps and directly increased the production of secondary metabolites, including phenolic and terpenoid compounds. Actin protein (ACT), elongation factor 1-α (EF1α), glyceraldehyde-3-phosphate dehydrogenase cytosolic (GAPC) and ubiquitin-conjugating enzyme (UBC) were used as traditional reference genes. UBC's suitability as the reference genes were verified in S. rechingeri. The study's results provide the foundation for gene expression analysis of savory and other species of Lamiaceae. Thus, the effective application of drought stress before harvesting can increase the quantity and quality of raw material.

Physiological responses and metal uptake of Miscanthus under cadmium/arsenic stress

The aim of this study is to explore the impact of cadmium (Cd) and arsenic (As) stress on physiological indexes and Cd/As uptake ability of Miscanthus, including Miscanthus sacchariflorus A0104, Miscanthus sinensis C0424 and C0640. Cd and As concentration showed significant hormesis effects on some physiological indexes, such as chlorophyll content, net photosynthetic rate, and MDA content. Compared with control group, Cd uptake can be most greatly enhanced by above fourfold with 150 mg/kg Cd treatment. As uptake of A0104 was increased by 3 ~ 33 folds with 200 mg/kg As treatment, C0424 was increased by 7-12 folds with 100 mg/kg As treatment, while C0640 was increased 1 ~ 6 folds with 250 mg/kg As treatment. The results also showed that C0640 was relatively better for the Cd remediation in the high Cd concentration (150 mg/kg) contaminated soil, while A0104 and C0424 were relatively better for the As remediation in the high As concentration (100 ~ 200 mg/kg) contaminated soil. Additionally, significantly (p < 0.05) close correlations were found among physiological indexes (except MDA content), while physiological indexes showed no significant relationship with the heavy metal contents in root, stem, and leaf.

Cadmium phytoextraction potential of king grass (Pennisetum sinese Roxb.) and responses of rhizosphere bacterial communities to a cadmium pollution gradient

Screening for tolerant and high biomass producing plants is important for phytoextraction efforts in remediating agricultural soils contaminated by heavy metals. We carried out a greenhouse experiment involving a soil cadmium (Cd) concentration gradient (0.1, 0.5, 1, 2, 4, and 8 mg kg^-1) to assess growth and phytoextraction capacity of king grass (Pennisetum sinese Roxb.) in soils contaminated by Cd and to explore changes in diversity and structure of rhizosphere soil bacterial communities in response to long-term Cd pollution. A significant positive relationship was observed between Cd concentrations in P. sinese stems, leaves, and roots and soil Cd concentration. The highest Cd concentrations in shoots and roots were 28.87 and 34.01 mg kg^-1, respectively, at 8 mg kg^-1of soil Cd supply. Total extraction amounts of Cd in P. sinese were 0.22-1.86 mg plant^-1 corresponding to treatment with 0.5-8 mg kg^-1 Cd. Most of the Cd was stored in shoots, and the largest accumulation was 1.56 mg plant^-1 with 54.02 g dry shoot weight. After phytoextraction, changes in rhizobacterial community composition were found with different levels of Cd application, whereas there were no clear trends in diversity and richness. Results of this study show the feasibility of P. sinese in accumulating Cd and provide support for its application in remediation of soil moderately contaminated by Cd.

Identification for the capability of Cd-tolerance, accumulation and translocation of 96 sorghum genotypes

Cadmium (Cd) pollution is a worldwide environmental problem which heavily threatens human health and food security. Sorghum, as one of the most promising energy crop, has been considered to be the source of high-quality feedstock for ethanol fuel. Ninety-six sorghum genotypes were investigated under hydroponic conditions to compare their capabilities of Cd-tolerance, accumulation and translocation for their potential in remediation of Cd contamination. Different genotypes varied largely in the tolerance to Cd stress with tolerance indexes ranked from 0.107 to 0.933. Great difference was also found in Cd uptake and accumulation with concentrations ranging from 19.0 to 202.4mg/kg in shoots and 277.0-898.3mg/kg in roots. The total amounts of Cd ranked from 6.1 to 25.8μg per plant and the highest translocation factor was over 4 times higher than the lowest one. The correlation analysis demonstrated that Cd concentration in shoot reflected the ability of Cd translocation and tolerance of sorghum, and the path coefficient analysis indicated that root biomass could be taken as a biomarker to evaluate Cd extraction ability of sorghum. The results in this study can facilitate the restoring of Cd contaminated areas by sorghum.

Morphophysiological characteristic analysis demonstrated the potential of sweet sorghum (Sorghum bicolor (L.) Moench) in the phytoremediation of cadmium-contaminated soils

Cadmium (Cd) contamination is a worldwide environmental problem, and remediation of Cd pollution is of great significance for food production as well as human health. Here, the responses of sweet sorghum cv. 'M-81E' to cadmium stress were studied for its potential as an energy plant in restoring soils contaminated by cadmium. In hydroponic experiments, the biomass of 'M-81E' showed no obvious change under 10 μM cadmium treatment. Cadmium concentration was the highest in roots of seedlings as well as mature plants, but in agricultural practice, the valuable and harvested parts of sweet sorghum are shoots, so promoting the translocation of cadmium to shoots is of great importance in order to improve its phytoremediation capacity. Further histochemical assays with dithizone staining revealed that cadmium was mainly concentrated in the stele of roots and scattered in intercellular space of caulicles. Moreover, the correlation analysis showed that Cd had a negative relationship with iron (Fe), zinc (Zn), and manganese (Mn) in caulicles and leaves and a positive relationship with Fe in roots. These results implied that cadmium might compete with Fe, Zn, and Mn for the transport binding sites and further prevent their translocation to shoots. In addition, transmission electron microscopic observations showed that under 100 μM cadmium treatment, the structure of chloroplast was impaired and the cell wall of vascular bundle cells in leaves and xylem and phloem cells in roots turned thicker compared to control. In summary, morphophysiological characteristic analysis demonstrated sweet sorghum can absorb cadmium and the growth is not negatively affected by mild level cadmium stress; thus, it is a promising material for the phytoremediation of cadmium-contaminated soils considering its economic benefit. This study also points out potential strategies to improve the phytoremediation capacity of sweet sorghum through genetic modification of transporters and cell wall components.

Impact of proline application on cadmium accumulation, mineral nutrition and enzymatic antioxidant defense system of Olea europaea L. cv Chemlali exposed to cadmium stress

Proline plays an important role in plant response to various environmental stresses. However, its involvement in mitigation of heavy metal stress in plants remains elusive. In this study, we examined the effectiveness of exogenous proline (10 and 20 mM) in alleviating cadmium induced inhibitory effects in young olive plants (Olea europaea L. cv. Chemlali) exposed to two Cd levels (10 and 30 mg CdCl2 kg(-1) soil). The Cd treatment induced substantial accumulation of Cd in both root and leaf tissues and a decrease in gas exchange, photosynthetic pigments contents, uptake of essential elements (Ca, Mg and K) and plant biomass. Furthermore, an elevation of antioxidant enzymes activities (superoxide dismutase, catalase, glutathione peroxydase) and proline content in association with relatively high amounts of hydrogen peroxide, thiobarbituric acid reactive substances and electrolyte leakage were observed. Interestingly, the application of exogenous proline alleviated the oxidative damage induced by Cd accumulation. In fact, Cd-stressed olive plants treated with proline showed an increase of antioxidant enzymes activities, photosynthetic activity, nutritional status, plant growth and oil content of olive fruit. Generally, it seems that proline supplementation alleviated the deleterious effects of young olive plants exposed to Cd stress.

Exogenous proline mediates alleviation of cadmium stress by promoting photosynthetic activity, water status and antioxidative enzymes activities of young date palm (Phoenix dactylifera L.)

The ability of exogenous compatible solutes, such as proline, to counteract cadmium (Cd) inhibitory effects in young date palm plants (Phoenix dactylifera L. cv Deglet Nour) was investigated. Two-year-old date palm plants were subjected for five months at different Cd stress levels (0, 10 and 30 mg CdCl2 kg(-1) soil) whether supplied or not with exogenous proline (20mM) added through the irrigation water. Different levels of Cd stress altered plant growth, gas exchanges and chlorophyll content as well as water status, but at different extent among them. In contrast, an increase of antioxidant enzymes activities of Cd-treated plants in association with high amounts of proline content, hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) and electrolyte leakage (EL) were observed. Interestingly, exogenous proline mitigated the adverse effects of Cd on young date palm. Indeed, it alleviated the oxidative damage induced by Cd accumulation and established better levels of plant growth, water status and photosynthetic activity. Moreover, proline-treated plants showed high antioxidant enzymes activities (superoxide dismutase, catalase and glutathione peroxydase) in roots and leaves as compared to Cd-treated plants.

The uptake and bioaccumulation of heavy metals by food plants, their effects on plants nutrients, and associated health risk: a review

Heavy metal contamination is a globally recognized environmental issue, threatening human life very seriously. Increasing population and high demand for food resulted in release of various contaminants into environment that finally contaminate the food chain. Edible plants are the major source of diet, and their contamination with toxic metals may result in catastrophic health hazards. Heavy metals affect the human health directly and/or indirectly; one of the indirect effects is the change in plant nutritional values. Previously, a number of review papers have been published on different aspects of heavy metal contamination. However, no related information is available about the effects of heavy metals on the nutritional status of food plants. This review paper is focused upon heavy metal sources, accumulation, transfer, health risk, and effects on protein, amino acids, carbohydrates, fats, and vitamins in plants. The literature about heavy metals in food plants shows that both leafy and nonleafy vegetables are good accumulators of heavy metals. In nonleafy vegetables, the bioaccumulation pattern was leaf > root ≈ stem > tuber. Heavy metals have strong influence on nutritional values; therefore, plants grown on metal-contaminated soil were nutrient deficient and consumption of such vegetables may lead to nutritional deficiency in the population particularly living in developing countries which are already facing the malnutrition problems.

Effects of mine wastewater irrigation on activities of soil enzymes and physiological properties, heavy metal uptake and grain yield in winter wheat

In China, coal-mining industries are mainly located in the water shortage areas including arid or semiarid areas. Mine wastewater is used for irrigation of agricultural land in these areas. However, few studies have been conducted to address ecological and food safety risks caused by mine wastewater irrigation. In this research, a pot experiment was performed to examine the effects of mine wastewater irrigation on soil enzymes, physiological properties of wheat and potential risks of heavy metal contamination to wheat crop. Plants were subjected to three mine wastewater irrigation treatments: leacheate of coal gangue (T1), coal-washing wastewater (T2) and precipitated coal-washing wastewater (T3). Plants irrigated with well water were taken as the control (CK). The results showed that mine wastewater irrigation caused adverse effects on soil enzymes, physiological properties and grain yield of winter wheat. At anthesis, T1, T2 and T3 treatments significantly reduced the activities of soil enzymes (urease, sucrase and catalase), root activity and net photosynthetic rate of wheat compared to CK. At maturity, grain yield was decreased by 17.8%, 15.4% and 9.8% by T1, T2 and T3, respectively, as compared to that of CK. Importantly, mine wastewater irrigation resulted in accumulation of heavy metals (Cr, Pb, Cu and Zn) in wheat grain. Contents of these heavy metals in grains of winter wheat subjected to mine wastewater irrigation were significantly higher than those in CK. The comprehensive contamination indexes of wheat grain in T1, T2 and T3 all reached high pollution level. Our results showed that mine wastewater irrigation significantly increased the pollution risk of heavy metals, thus unsuitable for crop irrigation.