Effects of silicon and copper on bamboo grown hydroponically

Assembly patterns and key taxa of bacterial communities in the rhizosphere soil of moso bamboo (Phyllostachys pubescens) under different Cd and Pb pollution

Moso bamboo is excellent candidate for cadmium (Cd)/lead (Pb) phytoremediation, while rhizosphere microbiome has significant impact on phytoremediation efficiency of host plant. However, little is known about the rhizosphere bacterial communities of moso bamboo in Cd/Pb contaminated soils. Therefore, this study investigated the assembly patterns and key taxa of rhizosphere bacterial communities of moso bamboo in Cd/Pb polluted and unpolluted soils, by field sampling, chemical analysis, and 16S rRNA gene sequencing. The results indicated α-diversity between Cd/Pb polluted and unpolluted soils showed a similar pattern (p > 0.05), while β-diversity was significantly different (p < 0.05). The relative abundance analysis indicated α-proteobacteria (37%) and actinobacteria (31%) were dominant in Cd/Pb polluted soils, while γ-proteobacteria (40%) and α-proteobacteria (22%) were dominant in unpolluted soils. Co-occurrence network analysis indicated microbial networks were less complex and more negative in polluted soils than in unpolluted soils. Mantel analysis indicated soil available phosphorus, organic matter, and available Pb were the most important environmental factors affecting microbial community structure. Correlation analysis showed 11 bacterial genera were significantly positively related to Cd/Pb. Overall, this study identified the bacterial community composition of bamboo rhizosphere in responding to Cd/Pb contamination and provides a theoretical basis for microbe-assistant phytoremediation in the future.

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.

Chromium phytoextraction using Phyllostachys pubescens (Moso Bamboo)

In this study, a bamboo species, the Phyllostachys pubescens - Moso Bamboo (MB) -, was selected for its heavy metals accumulation and translocation potential to restore Chromium (Cr)-contaminated soil. In order to evaluate the MB Chromium growth, tolerance and the potential for phytoremediation using MB to restore Cr-contaminated soil, pot experiments were carried out in simulated Mediterranean conditions in a laboratory, in a controlled environment, at a temperature of 20 °C. The results showed that MB growth rate was 4.28 cm/week on average, with an irrigation flow of 1.644 mm/d. MB tolerance was tested over a 12-week irrigation period with the addition of Cr-contaminated water. Cr removal from soil was 43% starting from a Cr content of approx. 200 mg/kg dry weight (dw) and the quantity of Cr per gram of root and rhizome was equal to 1.31 mg/g dw, while the quantity of Cr per gram of stem and leaves was equal to 0.86 mg/g dw, after 12 weeks. Pot experiments confirm that phytoremediation using plants such as MB provides an alternative approach for handling Cr-contaminated soil.

Silicon Fertigation Regimes Attenuates Cadmium Toxicity and Phytoremediation Potential in Two Maize (Zea mays L.) Cultivars by Minimizing Its Uptake and Oxidative Stress

Silicon (Si) is an important plant-derived metabolite that is significantly involved in maintaining the stability of a plant’s metabiological, structural and physiological characteristics under the abiotic stressed environment. We conducted the present study using maize (Zea mays L.) cultivars (Sadaf and EV-20) grown in sand artificially contaminated with cadmium (500 µM) in Hoagland’s nutrient solution to investigate its efficiency. Results from the present study evidenced that the toxic concentration of Cd in sand significantly reduced shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight by 88, 94, 89, 86 99 and 99%, respectively, in Sadaf while decreasing by 98, 97, 93, 99, 84 and 91%, respectively, in EV-20. Similarly, Cd toxicity decreased total chlorophyll and carotenoid content in both varieties of Z. mays. Moreover, the activities of various antioxidants (superoxidase dismutase, peroxidase and catalase) increased under the toxic concentration of Cd in sand which was manifested by the presence of membrane permeability, malondialdehyde (MDA), and hydrogen peroxide (H2O2). Results additionally showed that the toxic effect of Cd was more severe in EV-20 compared with Sadaf under the same conditions of environmental stresses. In addition, the increased concentration of Cd in sand induced a significantly increased Cd accumulation in the roots (141 and 169 mg kg−1 in Sadaf and EV-20, respectively), and shoots (101 and 141 mg kg−1 in Sadaf and EV-20, respectively), while; EV-20 accumulated higher amounts of Cd than Sadaf, with the values for both bioaccumulation factor (BAF) and translocation factor (TF) among all treatments being less than 1. The subsequent negative results of Cd injury can be overcome by the foliar application of Si which not only increased plant growth and biomass, but also decreased oxidative damage induced by the higher concentrations of MDA and H2O2 under a Cd-stressed environment. Moreover, external application of Si decreased the concentration of Cd in the roots and shoots of plants, therefore suggesting that the application of Si can ameliorate Cd toxicity in Z. mays cultivars and results in improved plant growth and composition under Cd stress by minimizing oxidative damage to membrane-bound organelles.

Phytoextraction of Cr(VI)-Contaminated Soil by Phyllostachys pubescens: A Case Study

This work presents the results of experimental tests to evaluate the effects of prolonged contamination by Cr on Moso Bamboo (MB) (Phyllostachys pubescens) and the adaptability of the MB to the Mediterranean climate. A preliminary test on the MB was developed in the laboratory, simulating irrigation under Mediterranean conditions (600 mm per year) and tropical conditions (1800 mm per year), to evaluate the rate of growth and the MB’s capability for Cr phytoextraction from contaminated soil. The tolerance of MB to Cr was also performed showing a good response of the plant to 100 mg Cr/L solution, utilized for irrigation of the pots. The results show that the rate of MB’s removal of Cr from soil ranged from 49.2% to 61.7% as a function of the soil degree of contamination, which varied from approx. 100 mg/kg to 300 mg/kg. The distribution of Cr in the various sections of the bamboo revealed that the greater percentage was present in rhizomes: 42%, equal to 114 mg Cr for 600 mm per year, and 50%, equal to 412 mg Cr for 1800 mm per year. A noteworthy diffusion of the metal towards the outermost parts of the plant was shown. The values of Cr retained in the stems and leaves of MB tissues were quite high and varied from 1100 mg/kg to 1700 mg/kg dry weight.

Analysis of the copper removal kinetics of the Philippine giant bamboo (Dendrocalamus asper) in hydroponics

Copper is the third most utilized metal and is a versatile resource with multiple beneficial uses, but it may also become toxic to aquatic life in excess amount. Thus, there is a need to develop methods to reduce the copper contamination in the environment, particularly in bodies of water. Phytoremediation using Dendrocalamus asper may offer an environment-benign and potentially effective method for copper removal though its effectiveness may take several years to materialize for this technology to become cost-effective. By growing D. asper in synthesized contaminated water and analyzing the change in the copper content of the substrate via atomic absorption spectrophotometry, the removal was found to be optimal at 20 ppm Cu and pH 5. The rate of removal was found to have an order of 2.71 and a kinetic constant of 0.0013 ppm^-1.71 day^-1. With this, it may be possible to estimate the treatment length of phytoremediation given an initial level of copper contamination and a target concentration.

Elucidating silicon-mediated distinct morpho-physio-biochemical attributes and organic acid exudation patterns of cadmium stressed Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem due to rapid development of social economy. Silicon (Si), being an important fertilizer element, has been found effective in enhancing plant tolerance against biotic and abiotic stresses. The present study investigated the extent to which different levels of Si modulated the Cd tolerance of Ajwain (Trachyspermum ammi L.) seedlings when maintained in artificially Cd spiked regimes. A pot experiment was conducted under controlled conditions for four weeks, by using sand, mixed with different levels of Cd i.e., 0, 1.5 and 3 mM together with the application of Si at 0, 1.5 and 3 mM levels to monitor different growth, gaseous exchange, oxidative stress, antioxidative responses, minerals accumulation, organic acid exudation patterns of T. ammi seedlings. Our results depicted that Cd addition to growth medium significantly decreased plant growth and biomass, gaseous exchange attributes and minerals uptake by T. ammi seedlings as compared to the plants grown without addition of Cd. However, Cd toxicity boosted the production of reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of oxidative stress in T. ammi seedlings and was also manifested by hydrogen peroxide (H₂O₂) contents and electrolyte leakage to the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) initially increased up to a Cd level of 1.5 mM but were significantly diminished at the highest Cd level of 3 mM. Results revealed that the anthocyanin and soluble proteins contents were decreased in seedlings grown under elevating Cd levels but increased the Cd accumulation of T. ammi roots and shoots. The negative impacts of Cd injury were reduced by the application of Si which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, minerals uptake together with diminished exudation of organic acids as well as oxidative stress indicators in roots and shoots of T. ammi by decreasing Cd retention in different plant parts. Research findings, therefore, suggested that Si application can ameliorate Cd toxicity in T. ammi seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

Ethylenediaminetetraacetic Acid (EDTA) Mitigates the Toxic Effect of Excessive Copper Concentrations on Growth, Gaseous Exchange and Chloroplast Ultrastructure of Corchorus capsularis L. and Improves Copper Accumulation Capabilities

Copper (Cu) is an important micronutrient for a plant’s normal growth and development. However, excess amount of Cu in the soil causes many severe problems in plants—which ultimately affect crop productivity and yield. Moreover, excess of Cu contents causes oxidative damage in the plant tissues by generating excess of reactive oxygen species (ROS). The present experiment was designed to investigate the phytoextraction potential of Cu, morpho-physiological features and biochemical reaction of jute (Corchorus capsularis L.) seedlings using ethylenediaminetetraacetic acid (EDTA) of 3 mM under different Cu levels (0 (control), 50 and 100 μM) in a hydroponic nutrient solution (Hoagland). Our results showed that elevated Cu rates (50 and 100 μM) in the nutrient solution significantly reduced plant height, fresh and dry biomass, total chlorophyll content and gaseous exchange attributes in C. capsularis seedlings. As the concentration of Cu in the medium increased (50 and 100 μM), the level of malondialdehyde (MDA) and oxidative stress in C. capsularis seedlings also increased, which could have been controlled by antioxidant activity in particular plant cells. In addition, rising Cu concentration in the nutrient solution also increased Cu uptake and accumulation in roots and leaves as well as affected the ultrastructure of chloroplast of C. capsularis seedlings. The addition of EDTA to the nutrient solution significantly alleviated Cu toxicity in C. capsularis seedlings, showing a significantly increase in plant growth and biomass. MDA contents was not significantly increased in EDTA-induced plants, suggesting that this treatment was helpful in capturing ROS and thereby reducing ROS in in C. capsularis seedlings. EDTA modification with Cu, although the bioaccumulation factor in roots and leaves and translocation factor for the leaves of C. capsularis seedlings has significantly increased. These results indicate that C. capsularis has considerable potential to cope with Cu stress and is capable of removing a large quantity of Cu from the Cu-contaminated soil while using EDTA is a useful strategy to increase plant growth and biomass with Cu absorption capabilities.

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.

Phytoremediation potential and copper uptake kinetics of Philippine bamboo species in copper contaminated substrate

The phytoremediation potential of three bamboo species, i.e. Bambusa merilliana, Bambusa blumeana, and Dendrocalamus asper, were evaluated for their total Cu uptake ability in hydroponics. Dendrocalamus asper proved to be the most efficient in terms of Cu phytoremediating potential with a constant positive uptake of 80 μM in a contaminated substrate and a bioconcentration factor of 50.57. Copper accumulation was found to concentrate the most in the roots compared to the amount translocated in the shoots. Analysis of the Cu uptake of D. asper roots at varying concentrations of Cu contamination (40, 80 and 120 μM) allowed for the fitting of the kinetics of Cu uptake and removal with existing kinetic models. The rate of copper removal per mass of plant was the best for the 0^th order model in the 80 μM solution with an R² of 0.954 and rate constant of 3.136 mg-kg^-1d^-1. The accumulation of Cu within the roots on day 7 (7d) followed the Michaelis-Menten model with an R² of 0.970. The Michaelis-Menten constant (K_M) was 4.87 mg/L and maximum accumulation velocity (Vmax) was 66.26 mg Cu-kg^-1-day^-1. Results suggest that D. asper is a potential hyperaccumulator plant that can be used in clean-up of domestic and industrial wastes present along river systems in the Philippines.

Silicon and Plants: Current Knowledge and Technological Perspectives

Elemental silicon (Si), after oxygen, is the second most abundant element in the earth's crust, which is mainly composed of silicates. Si is not considered essential for plant growth and development, however, increasing evidence in the literature shows that this metalloid is beneficial to plants, especially under stress conditions. Indeed Si alleviates the toxic effects caused by abiotic stresses, e.g., salt stress, drought, heavy metals, to name a few. Biogenic silica is also a deterrent against herbivores. Additionally, Si ameliorates the vigor of plants and improves their resistance to exogenous stresses. The protective role of Si was initially attributed to a physical barrier fortifying the cell wall (e.g., against fungal hyphae penetration), however, several studies have shown that the action of this element on plants is far more complex, as it involves a cross-talk with the cell interior and an effect on plant metabolism. In this study the beneficial role of Si on plants will be discussed, by reviewing the available data in the literature. Emphasis will be given to the protective role of Si during (a)biotic stresses and in this context both priming and the effects of Si on endogenous phytohormones will be discussed. A whole section will be devoted to the use of silica (SiO₂) nanoparticles, in the light of the interest that nanotechnology has for agriculture. The paper also discusses the potential technological aspects linked to the use of Si in agriculture and to modify/improve the physical parameters of plant fibers. The study indeed provides perspectives on the use of Si to increase the yield of fiber crops and to improve the thermal stability and tensile strength of natural fibers.

Copper induced oxidative stresses, antioxidant responses and phytoremediation potential of Moso bamboo (Phyllostachys pubescens)

Moso bamboo is recognized as phytoremediation plant due to production of huge biomass and high tolerance in stressed environment. Hydroponics and pot experiments were conducted to investigate mechanism of copper tolerance and to evaluate copper accumulation capacity of Moso bamboo. In hydroponics experiment there was non significant variation in MDA contents of leaves compared with control. SOD and POD initially indicated enhancing trend with application of 5 μM Cu and then decreased consistently with application of 25 and 100 μM Cu. Application of each additional increment of copper have constantly enhanced proline contents while maximum increase of proline was observed with application of 100 μM copper. In pot experiment chlorophyll and biomass initially showed increasing tendency and decreased gradually with application of each additional increment of Cu. Normal growth of Moso bamboo was observed with application of 100 mg kg⁻¹ copper. However, additional application of 300 or 600 mg kg⁻¹ copper had significantly inhibited growth of Moso bamboo. The concentration of Cu in Moso bamboo has attained the levels of 340, 60, 23 mg kg⁻¹ in roots, stems and leaves respectively. The vacuoles were the main organs which accumulated copper and reduced toxicity of copper as studied by TEM-DEX technology.

Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: A review

In present era, heavy metal pollution is rapidly increasing which present many environmental problems. These heavy metals are mainly accumulated in soil and are transferred to food chain through plants grown on these soils. Silicon (Si) is the second most abundant element in the soil. It has been widely reported that Si can stimulate plant growth and alleviate various biotic and abiotic stresses, including heavy metal stress. Research to date has explored a number of mechanisms through which Si can alleviate heavy metal toxicity in plants at both plant and soil levels. Here we reviewed the mechanisms through which Si can alleviate heavy metal toxicity in plants. The key mechanisms evoked include reducing active heavy metal ions in growth media, reduced metal uptake and root-to-shoot translocation, chelation and stimulation of antioxidant systems in plants, complexation and co-precipitation of toxic metals with Si in different plant parts, compartmentation and structural alterations in plants and regulation of the expression of metal transport genes. However, these mechanisms might be associated with plant species, genotypes, metal elements, growth conditions, duration of the stress imposed and so on. Further research orientation is also discussed.

Effect of silicon on wheat seedlings (Triticum turgidum L.) grown in hydroponics and exposed to 0 to 30 µM Cu

Aqueous Si limits Cu uptake by a Si-accumulating plant via physicochemical mechanisms occurring at the root level. Sufficient Si supply may alleviate Cu toxicity in Cu-contaminated soils. Little information is available on the role of silicon (Si) in copper (Cu) tolerance while Cu toxicity is widespread in crops grown on Cu-contaminated soils. A hydroponic study was set up to investigate the influence of Si on Cu tolerance in durum wheat (Triticum turgidum L.) grown in 0, 0.7, 7.0 and 30 µM Cu without and with 1.0 mM Si, and to identify the mechanisms involved in mitigation of Cu toxicity. Si supply alleviated Cu toxicity in durum wheat at 30 µM Cu, while Cu significantly increased Si concentration in roots. Root length, photosynthetic pigments concentrations, macroelements, and organic anions (malate, acetate and aconitate) in roots, were also increased. Desorption experiments, XPS analysis of the outer thin root surface (≤100 Å) and µXRF analyses showed that Si increased adsorption of Cu at the root surface as well as Cu accumulation in the epidermis while Cu was localised in the central cylinder when Si was not applied. Copper was not detected in phytoliths. This study provides evidences for Si-mediated alleviation of Cu toxicity in durum wheat. It also shows that Si supplementation to plants exposed to increasing levels of Cu in solution induces non-simultaneous changes in physiological parameters. We propose a three-step mechanism occurring mainly at the root level and limiting Cu uptake and translocation to shoots: (i) increased Cu adsorption onto the outer thin layer root surface and immobilisation in the vicinity of root epidermis, (ii) increased Cu complexation by both inorganic and organic anions such as aconitate and, (iii) limitation of translocation through an enhanced thickening of a Si-loaded endodermis.