Evaluation of hyperaccumulation potentials to cadmium (Cd) in six ornamental species (compositae).

Phytoremediation is considered as a promising soil remediation technique. In the present study, the growth responses, cadmium (Cd) accumulation and uptake capability of six popular compositae species, namely, Taraxacum mongolicum Hand.-Mazz., Tagetes erecta L., Tagetes patula L., Zinnia elegans Jacq., Centaurea cyanus L. and Gerbera jamesonii Bolus under Cd stress were investigated. Among the six compositae species, the growth of T. erecta L. and T. patula L. improved under 10 mg kg-1 Cd exposure in term of the total biomass and height increased along with the increased Cd concentration in soil, and the growth of the two plants had no significant differences at the high Cd concentration (100 mg kg-1), which indicated that they have good tolerance to Cd toxicity. At the same time, the two plants have higher biomass than four other plants. Furthermore, they can accumulate Cd above 100 µg g-1 dry tissue, which is the threshold value of a Cd-hyperaccumulator, and have higher Cd uptake ability, translocation factor (TF) and bioconcentration factor (BCF) values. According to these traits, it was shown that T. erecta L. and T. patula L. had strong tolerance and accumulation capability to Cd, therefore they can become potential hyperaccumulators in phytoremediation of Cd-contaminated soils.

Regulatory Effects of Elevated Carbon Dioxide on Growth and Biochemical Responses to Ozone Stress in Chinese Pine (Pinus tabulaeformis Carr.).

This study examined whether carbon dioxide (CO2) might alleviate ozone (O3) injury to the dominant coniferous forest species of northern China, Pinus tabulaeformis Carr. After 90 days O3 exposure, biomass and net photosynthetic rate (Pn) decreased significantly by 24.44 % and 42.89 % compared with the control. A significant increase in malondialdehyde (MDA) was shown, suggesting cell membrane damage and oxidative stress. However, the positive responses of biomass dry weight, antioxidative enzymes and soluble sugar contents under elevated CO2 alone and the combination of elevated CO2 and O3 were observed, indicating that CO2 could ameliorate O3-induced injury. The study provided increasing evidence that moderately elevated CO2 levels may have a beneficial effect on the forest ecosystem to respond to global climate change.

A meta-analysis of elevated O3 effects on herbaceous plants antioxidant oxidase activity.

Increases in near-surface ozone (O3) concentrations is a global environmental problem. High-concentration O3 induces stress in plants, which can lead to visible damage to plants, reduced photosynthesis, accelerated aging, inhibited growth, and can even plant death. However, its impact has not been comprehensively evaluated because of the response differences between individual plant species, environmental O3 concentration, and duration of O3 stress in plants. We used a meta-analysis approach based on 31 studies 343 observations) to examine the effects of elevated O3 on malondialdehyde (MDA), superoxide dismutase (SOD), and peroxidase (POD) activities in herbaceous plants. Globally, important as they constitute the majority of the world's food crops. We partitioned the variation in effect size found in the meta-analysis according to the presence of plant species (ornamental herb, rice, and wheat), O3 concentration, and duration of O3 stress in plants. Our results showed that the effects of elevated O3 on plant membrane lipid peroxidation depending on plant species, O3 concentration, and duration of O3 stress in plants. The wheat SOD and POD activity was significantly lower compared to the herbs and rice (P<0.01). The SOD activity of all herbaceous plants increased by 34.6%, 10.5%, and 26.3% for exposure times to elevated O3 environments of 1-12, 13-30, and 31-60 days, respectively. When the exposure time was more than 60 days, SOD activity did not increase but significantly decreased by 12.1%. However, the POD activity of herbaceous plants increased by 30.4%, 57.3%, 21.9% and 5.81%, respectively, when exposure time of herbaceous plants in elevated O3 environment was 1-12, 13-30, 31-60 and more than 60 days. Our meta-analysis revealed that (1) rice is more resistant to elevated O3 than wheat and ornamental herbs likely because of the higher activity of antioxidant components (e.g., POD) in the symplasts, (2) exposure to elevated O3 concentrations for >60 days, may result in antioxidant SOD lose its regulatory ability, and the antioxidant component POD in the symplast is mainly used to resist O3 damage, and (3) the important factors affected the activity of SOD and POD in plants were not consistent: the duration of O3 stress in plants was more important than plant species and O3 concentration for SOD activity. However, for POD activity, plant species was the most important factor.

Hormesis phenomena under Cd stress in a hyperaccumulator--Lonicera japonica Thunb.

A hydroponic experiment was carried out to investigate possible hormetic response induced by cadmium (Cd) in a potential hyperaccumulator-Lonicera japonica Thunb. The results showed that Cd at low concentrations induced a significant increase in plant growth, leaf water content and content of photosynthetic pigments in L. japonica, but decreased them at high concentrations, displayed inverted U-shaped dose response curves, confirming a typical biphasic hormetic response. The U-shaped dose response curves were displayed in malondialdehyde (MDA) and electrolyte leakage in leaves at low doses of Cd, indicating reduce oxidative stress and toxic effect. The increase of superoxide dismutase (SOD) and catalase (CAT) activities was observed along with the increased Cd concentration, indicative of increase in anti-oxidative capacity that ensures redox homeostasis is maintained. After 28 days exposure to 10 mg L(-1) Cd, stem and leaf Cd concentrations reached 502.96 ± 28.90 and 103.22 ± 5.62 mg kg(-1) DW, respectively and the plant had high bioaccumulation coefficient (BC) and translocation factor (TF'). Moreover, the maximum TF value was found at 2.5 mg L(-1) Cd treatment, implying that low Cd treatment improved the ability to transfer Cd from medium via roots to aerial structures. Taking together, L. japonica could be considered as a new plant to investigate the underlying mechanisms of hormesis and Cd tolerance. Our results suggest that hormetic effects should be taken into consideration in phytoremediation of Cd-contaminated soil.

Hormesis Responses of Growth and Photosynthetic Characteristics in Lonicera japonica Thunb. to Cadmium Stress: Whether Electric Field Can Improve or Not?

"Hormesis" is considered a dose-response phenomenon mainly observed at hyperaccumulator plants under heavy metals stress. In this study, the effects of electric fields on hormesis responses in Lonicera japonica Thunb. under cadmium (Cd) treatments were investigated by assessing the plant growth and photosynthetic characteristics. Under Cd treatments without electric fields, the parameters of plant growth and photosynthetic characteristics increased significantly when exposed to 5 mg L-1 Cd, and decreased slightly when exposed to 25 mg L-1 Cd, showing an inverted U-shaped trend, which confirmed that low concentration Cd has a hormesis effect on L. japonica. Under electric fields, different voltages significantly promoted the inverted U-shaped trend of the hormesis effect on the plant, especially by 2 V cm-1 voltage. Under 2 V cm-1 voltage, the dry weight of the root and leaf biomass exposed to 5 mg L-1 Cd increased significantly by 38.38% and 42.14%, and the photosynthetic pigment contents and photosynthetic parameters were also increased significantly relative to the control, indicating that a suitable electric field provides better improvements for the hormesis responses of the plant under Cd treatments. The synergistic benefits of the 5 mg L-1 Cd and 2 V cm-1 electric field in terms of the enhanced hormesis responses of growth and photosynthetic characteristics could contribute to the promoted application of electro-phytotechnology.

Ameliorating Effects of Graphene Oxide on Cadmium Accumulation and Eco-Physiological Characteristics in a Greening Hyperaccumulator (Lonicera japonica Thunb.).

Graphene oxide (GO), as a novel carbon-based nanomaterial (CBN), has been widely applied to every respect of social life due to its unique composite properties. The widespread use of GO inevitably promotes its interaction with heavy metal cadmium (Cd), and influences its functional behavior. However, little information is available on the effects of GO on greening hyperaccumulators under co-occurring Cd. In this study, we chose a typical greening hyperaccumulator (Lonicera japonica Thunb.) to show the effect of GO on Cd accumulation, growth, net photosynthesis rate (Pn), carbon sequestration and oxygen release functions of the plant under Cd stress. The different GO-Cd treatments were set up by (0, 10, 50 and 100 mg L-1) GO and (0, 5 and 25 mg L-1) Cd in solution culture. The maximum rate of Cd accumulation in the roots and shoots of the plant were increased by 10 mg L-1 GO (exposed to 5 mg L-1 Cd), indicating that low-concentration GO (10 mg L-1) combined with low-concentration Cd (5 mg L-1) might stimulate the absorption of Cd by L. japonica. Under GO treatments without Cd, the dry weight of root and shoot biomass, Pn value, carbon sequestration per unit leaf area and oxygen release per unit leaf area all increased in various degrees, especially under 10 mg L-1 GO, were 20.67%, 12.04%, 35% and 28.73% higher than the control. Under GO-Cd treatments, it is observed that the cooperation of low-concentration GO (10 mg L-1) and low-concentration Cd (5 mg L-1) could significantly stimulate Cd accumulation, growth, photosynthesis, carbon sequestration and oxygen release functions of the plant. These results indicated that suitable concentrations of GO could significantly alleviate the effects of Cd on L. japonica, which is helpful for expanding the phytoremediation application of greening hyperaccumulators faced with coexistence with environment of nanomaterials and heavy metals.

Effects of Cadmium Stress on Carbon Sequestration and Oxygen Release Characteristics in A Landscaping Hyperaccumulator-Lonicera japonica Thunb.

The carbon sequestration and oxygen release of landscape plants are dominant ecological service functions, which can play an important role in reducing greenhouse gases, improving the urban heat island effect and achieving carbon peaking and carbon neutrality. In the present study, we are choosing Lonicera japonica Thunb. as a model plant to show the effects of Cd stress on growth, photosynthesis, carbon sequestration and oxygen release characteristics. Under 5 mg kg-1 of Cd treatment, the dry weight of roots and shoots biomass and the net photosynthetic rate (PN) in L. japonica had a significant increase, and with the increase in Cd treatment concentration, the dry weight of roots and shoots biomass and PN in the plant began to decrease. When the Cd treatment concentration was up to 125 mg kg-1, the dry weight of root and shoots biomass and PN in the plant decreased by 5.29%, 1.94% and 2.06%, and they had no significant decrease compared with the control, indicating that the plant still had a good ability for growth and photoenergy utilization even under high concentrations of Cd stress. The carbon sequestration and oxygen release functions in terms of diurnal assimilation amounts (P), carbon sequestration per unit leaf area (WCO2), oxygen release per unit leaf area (WO2), carbon sequestration per unit land area (PCO2) and oxygen release per unit land area (PO2) in L. japonica had a similar change trend with the photosynthesis responses under different concentrations of Cd treatments, which indicated that L. japonica as a landscaping Cd-hyperaccumulator, has a good ability for carbon sequestration and oxygen release even under high concentrations of Cd stress. The present study will provide a useful guideline for effectively developing the ecological service functions of landscaping hyperaccumulators under urban Cd-contaminated environment.

Electric Field-Enhanced Cadmium Accumulation and Photosynthesis in a Woody Ornamental Hyperaccumulator-Lonicera japonica Thunb.

The multi-system of electro-phytotechnology using a woody ornamental cadmium (Cd) hyperaccumulator (Lonicera japonica Thunb.) is a new departure for environmental remediation. The effects of four electric field conditions on Cd accumulation, growth, and photosynthesis of L. japonica under four Cd treatments were investigated. Under 25 and 50 mg L-1 Cd treatments, Cd accumulation in L. japonica was enhanced significantly compared to the control and reached 1110.79 mg kg-1 in root and 428.67 mg kg-1 in shoots influenced by the electric field, especially at 2 V cm-1, and with higher bioaccumulation coefficient (BC), translocation factor (TF), removal efficiency (RE), and the maximum Cd uptake, indicating that 2 V cm-1 voltage may be the most suitable electric field for consolidating Cd-hyperaccumulator ability. It is accompanied by increased root and shoots biomass and photosynthetic parameters through the electric field effect. These results show that a suitable electric field may improve the growth, hyperaccumulation, and photosynthetic ability of L.japonica. Meanwhile, low Cd supply (5 mg L-1) and medium voltage (2 V cm-1) improved plant growth and photosynthetic capacity, conducive to the practical application to a plant facing low concentration Cd contamination in the real environment.

Effects of cadmium hyperaccumulation on the concentrations of four trace elements in Lonicera japonica Thunb.

Hyperaccumulators are important in the phytoremediation of cadmium (Cd)-contaminated soil. In this study, Cd accumulation and the interactions between Cd and four other trace elements (Fe, Mn, Cu, and Zn) in Lonicera japonica Thunb. were investigated. As a result of exposure to soil containing 50 mg kg(-1) Cd, stem and shoot Cd concentrations reached 344.49 ± 0.71 and 286.12 ± 9.38 µg g(-1) DW respectively, without showing symptoms of visible damage to the plants. This suggests that L. japonica has a strong tolerance to Cd. It is proposed that trace metal elements are involved in the Cd-detoxification mechanisms shown by hyperaccumulators. There is a synergistic interaction in accumulation and translocation between Cd and Fe and a significantly negative correlation between Cd and Cu or Zn concentrations in L. japonica plant tissues. The imbalanced trace element concentrations influences detoxification processes to Cd, therefore, L. japonica could be considered as a new Cd-hyperaccumulator model to investigate the metal tolerance strategies of plants.

Hormetic Responses of Lonicera Japonica Thunb. To Cadmium Stress.

The hormetic responses of Lonicera japonica Thunb. to cadmium (Cd) stress were investigated in a hydroponic experiment. The present results showed that root length and total biomass dry weight increased in comparison with the control at low concentrations Cd. The height of the plant exposed to 2.5 and 5 mg L(-1) Cd increased significantly by 11.9% and 12.8% relative to the control, and with the increase of Cd concentrations in the medium, plant height began to decrease. The responses of photosynthetic pigments contents and relative water content to Cd stress had a similar trend, which all showed significantly an inverted U-shaped dose-response curve and confirmed that the stimulatory effect of low concentrations Cd occurred in the plant. Furthermore, L. japonica, as a new Cd-hyperaccumulator, could be considered as a new plant model to study the underlying mechanisms of the hormesis.

Ecotoxicological responses of three ornamental herb species to cadmium.

Cadmium is one of the most toxic elements. The ideal vegetal cover should be ensured by the selection of appropriate plant species for successful phytoremediation. In the present study, the ecotoxicological effects of Cd on the following 3 ornamental herbs were investigated: Italian ryegrass (Lolium multiflorum Lam.), white clover (Trifolium repens L.), and alfalfa (Medicago sativa L.). Based on the inhibition rate of seed germination, root and shoot elongation, early seedling growth, median inhibition concentration (IC50) values, and index of tolerance (IT) values, ecotoxicological indicators were determined. The results showed that 10 µM to 50 µM Cd had little effect on seed germination or root and shoot elongation of the 3 ornamental herbs (p > 0.01). With an increase in Cd concentrations, alfalfa (M. sativa) was the most sensitive to Cd toxicity in terms of seed germination and root elongation. Based on the IC50 of root elongation, Italian ryegrass (L. multiflorum) was the least sensitive to Cd. Based on the IC50 of seed germination and shoot elongation, white clover had the least sensitivity to Cd. Among the 3 ornamental herbs, based on the IC50 of seed germination and root and shoot elongation, alfalfa (M. sativa) was all the most sensitive plant. According to the index of tolerance, Italian ryegrass (L. multiflorum) was the most tolerant plant.

[Hormesis effect of cadmium on Lonicera japonica].

A hydroponic experiment was conducted to study the growth characteristics of Lonicera japonica under the stress of different concentrations (0, 0.5, 2.5, 5, 10, and 25 mg L-1 ) cadmium (Cd), aimed to explore the hormesis effect of low concentrations Cd on L. japonica. At < or =5 mg L-1 of Cd, the maximum root length, plant dry biomass, and the contents of chlorophyll a, chlorophyll b, and carotenoid of L. japonica increased significantly, with the increment being 13. 6%, 11.7%, 14. 0% ,10. 8%, and 54. 5%, respectively, as compared with the control. <5 mg L-1 of Cd also had a definite positive effect on the leaf water content. At> or = 10 mg L-1 of Cd, the growth of L. japonica was inhibited significantly. When exposed to 25 mg L-1 of Cd, the shoot Cd concentration of L. japonica reached 622. 93 mg kg-1 , suggesting that L. japonica had a strong capacity of Cd-hyperaccumulation. The dose range of the hormesis effect of Cd on L. japonica was 0.5-5 mg L-1 of Cd.

[Effects of cadmium stress on the growth and physiological characteristics of Lonicera japonica].

By using hydroponics, the growth and physiological characteristics of Lonicera japonica at different concentrations (0, 5, 10, 25, and 50 mg x L(-1)) of cadmium (Cd) were studied. The results showed that compared with the control, Cd stress had lesser effects on the growth of L. japonica. Within the range of test Cd concentrations, L. japonica biomass had less difference (P > 0.05) with the control, and at low concentration of Cd (5 mg x L(-1)), the total biomass and the biomasses of leaf and root were increased by 1.25%, 2.88 and 2.33%, respectively, illustrating that L. japonica had stronger resistance against Cd. Under low concentration Cd stress, the water content and soluble protein content in plant organs had some decrease, while the malondialdehyde (MDA) content in root and leaf increased by 51.90% and 23.07%, respectively, leaf chlorophyll and carotenoid contents increased by 15.87% and 24.89%, respectively, and superoxide dismutase (SOD) activity increased significantly. With increasing Cd concentration, the chlorophyll and carotenoid contents and SOD activity decreased to some extent.

Accumulation and tolerance characteristics of cadmium in a potential hyperaccumulator--Lonicera japonica Thunb.

Phytoremediation using hyperaccumulators is a promising technique of removing soil pollutants. In the study, growth responses, cadmium (Cd) accumulation capability and physiological mechanisms of Lonicera japonica Thunb. under Cd stress were investigated. Exposed to 5 and 10 mg L(-1) Cd, the plants did not show any visual symptoms, furthermore, the height, dry biomass of leaves, roots and total and the chlorophyll (CHL) content were obtained different grade increase. When the concentration of Cd was up to 50 mg L(-1), the height, dry biomass of leaves and roots had not significant differences compared with the control. The indexes of tolerance (IT) were all above 0.8. The maintenance of high superoxide dismutase (SOD) and catalase (CAT) activities was observed along with the increased Cd concentration, suggesting strong internal detoxification mechanisms inside plant cells. After 21 days exposure to 25 mg L(-1) Cd, stem and shoot Cd concentrations reached 344.49+/-0.71 and 286.12+/-9.38 microg g(-1) DW, respectively and the plant had higher bioaccumulation coefficient (BC) and translocation factor (TF). According to these results, it was shown L. japonica had strong tolerance and accumulation capability to Cd, therefore it is a potential Cd-hyperaccumulator.