Is vetiver grass of interest for the remediation of Cu and Cd to protect marketing gardens in Burkina Faso?

Effect of silicon on root growth, ionomics and antioxidant performance of maize roots exposed to As toxicity

Nowadays, one of the biggest challenges of plant physiology is to find out the ways how to mitigate negative impacts of abiotic stress on plants. It is the pollution of groundwater or soil by various metals and metalloids that significantly affects the quality of life. Both arsenic (As) and silicon (Si) are metalloids - while the first one is toxic in general, the latter one is considered as beneficial for plants suffering from various kinds of stresses. The aim of our work was to elucidate the growth and development of young maize (Zea mays L.) plants exposed to both of these metalloids simultaneously. Experiments were focused on the comparison of root growth and biomass allocation, changes in uptake of macro- and micronutrients, visualisation of free radicals along with monitoring of the dynamics of main antioxidant enzymes activity in roots. The results showed that increasing concentration of As (75 and 150 μM As) severely inhibited root length and the amount of biomass, and addition of Si (2.5 mM) to the medium containing As did not have a significant effect on root growth. Similarly, the application of Si did not influence the uptake of macro- and microelements into the roots (mainly Ca, P, K, Mo, Cu, Zn and Ni) which was mostly decreased due to As. On the other hand, Si significantly decreased the presence of both superoxide and hydrogen peroxide in roots that suffered from As toxicity. Although the overall growth of maize plants was not improved by Si amendment, we assume that Si might affect the functionality of key antioxidant enzymes in time, and in this way at least partially help to overcome negative effects of As on maize roots.

Cadmium phytoextraction by Helianthus annuus (sunflower), Brassica napus cv Wichita (rapeseed), and Chyrsopogon zizanioides (vetiver)

The use of phytoextraction plant species to accumulate soil metals into harvestable plant parts is a method used for managing soils with high cadmium (Cd). We evaluated three Cd accumulating species recently recommended for such use in cacao farms where Cd removal is needed to maintain markets: Helianthus annuus (sunflower), Brassica napus (rapeseed), and Chyrsopogon zizanioides (vetiver). Plants were grown in two greenhouse pot experiments with different Cd-spiked growth media: (sand plus perlite) and a natural soil. Plant total Cd and Cd uptake in shoot biomass of all species, across both experiments, increased linearly with increasing amounts of added Cd. Rapeseed had the highest plant total Cd and sunflower had the highest Cd uptake in shoot biomass. The highest application of Cd corresponded to the highest plant total Cd and shoot biomass Cd uptake, regardless of species. The bioconcentration factor (BCF) for each species increased in a curvilinear manner with added Cd, with maximum BCF values for plants grown in the sand and perlite matrix at 2.5 mg kg^-1 added Cd and in the natural soil at 5.0 mg kg^-1 added Cd. We conclude that the Cd uptake (shoot biomass only) capability of the three species examined is greatest for sunflower given its increased uptake with Cd additions, its BCF value > 1, and lack of observed visual Cd toxicity symptoms, fungus and insect damage. Although these species had BCF >1, the potential annual removal of Cd would have been too small to support a meaningful phytoextraction practice.

Influence of CaO-activated silicon-based slag amendment on the growth and heavy metal uptake of vetiver grass (Vetiveria zizanioides) grown in multi-metal-contaminated soils

Few plant species used for revegetation grow well in multi-metal-contaminated soils. Vetiver grass (Vetiveria zizanioides) is known to be tolerant of heavy metals. Vetiver has been reported to be effective for revegetation and heavy metal phytoextraction by applying targeted amendments due to its large biomass. In this study, a greenhouse vetiver pot experiment and soil incubation were performed to investigate the growth and Cd, Cr, Cu, Pb, and Zn uptake of vetiver grown in multi-metal-contaminated soils treated with a CaO-activated Si-based slag amendment (0, 0.5, 1.0, and 2.0% w/w). The results showed that the effects of slag amendment on plant growth and heavy metal uptake and distribution were dependent on the amendment dosages and metal species. Although vetiver could grow in contaminated soils, its growth was obviously inhibited. The slag amendment enhanced the vetiver growth and the highest biomass (2.62-fold over the control) was determined at a 1.0% amendment rate. The slag amendment improved plant growth by alleviating the toxicity of heavy metals in plants. This result was mainly attributed to the increases in soil pH and citric acid-extractable Si caused by alkaline amendment. The results suggest that vetiver can be applied to remediate multi-metal-contaminated soils in conjunction with the application of CaO-activated Si-based slag amendment.

The enhancement by arbuscular mycorrhizal fungi of the Cd remediation ability and bioenergy quality-related factors of five switchgrass cultivars in Cd-contaminated soil

A greenhouse experiment was carried out to investigate the effects of arbuscular mycorrhizal fungi (AMF) on the growth, P and Cd concentrations and bioenergy quality-related factors of five cultivars of switchgrass, including three lowland cultivars (Alamo (Ala), Kanlow (Kan), Performer (Per)) and two highland cultivars (Blackwell (Bw), Summer (Sum)), with 0, 1 and 10 mg/kg Cd addition levels. The results showed that AMF inoculation notably increased the biomass and P concentrations of all the cultivars. The Cd concentrations in the roots were higher than those in the shoots of all cultivars irrespective of inoculation, but the AMF had different effects on Cd accumulation in highland and lowland cultivars. AMF inoculation decreased the shoot and root concentrations in Ala and Kan, increased the shoot and root concentrations of Cd in Bw and Sum, and increased shoot Cd concentrations and decreased root Cd concentrations in Per. The highest Cd concentrations were detected in the roots of Bw and in the shoots of Sum with AMF symbiosis. Bw contained the highest total extracted Cd which was primarily in the roots. Ala had the second highest extracted Cd in the shoots, reaching 32% with 1 mg/kg of added Cd, whereas Sum had the lowest extracted Cd. AMF symbiosis had varied effects on bioenergy quality-related factors: for example, AMF decreased the ash lignin content in Ala and the C/N in Sum, increased the nitrogen, gross calorie values, and maintained the hemicellulose and cellulose contents in all cultivars with all tested concentrations of Cd. A principal component analysis (PCA) showed that AMF inoculation could enhance, weaken or transform (positive-negative, PC1-PC2) the correlations of these factors with the principle components under Cd stress. Therefore, AMF symbiosis enhanced the growth of different cultivars of switchgrass, increased/decreased Cd accumulation, promoted Cd extraction, and regulated the bioenergy quality-related factors in Cd-polluted areas. Bw is a suitable cultivar for phytostabilization due to high root Cd stabilization, whereas Ala is an appropriate cultivar for phytoremediation of less polluted areas because of its high Cd extraction and excellent bioenergy quality.

Vetiver plantlets in aerated system degrade phenol in illegally dumped industrial wastewater by phytochemical and rhizomicrobial degradation

This research evaluated the feasibility of using vetiver plantlets (Vetiveria zizanioides (L.) Nash) on a floating platform with aeration to degrade phenol (500 mg/L) in illegally dumped industrial wastewater (IDIWW). The IDIWW sample was from the most infamous illegal dumping site at Nong Nae subdistrict, Phanom Sarakham district, Chachoengsao province, Thailand. Laboratory results suggested that phenol degradation by vetiver involves two phases: Phase I, phytopolymerization and phyto-oxidation assisted by root-produced peroxide (H₂O₂) and peroxidase (POD), followed by phase II, a combination of phase I with enhanced rhizomicrobial degradation. The first 360-400 h of phenol degradation were dominated by phytopolymerization and phyto-oxidation yielding particulate polyphenols (PPP) or particulate organic matter (POM) as by-products, while phenol decreased to around 145 mg/L. In Phase II, synergistically, rhizomicrobial growth was ∼100-folds greater on the roots of the vetiver plantlets than in the IDIWW and participated in the microbial degradation of phenol at this lower phenol concentration, increasing the phenol degradation rate by more than three folds. This combination of phytochemical and rhizomicrobiological processes eliminated phenol in IDIWW in less than 766 h (32 days), while without the vetiver plantlets, phenol degradation by aerated microbial degradation alone may require 235 days. To our knowledge, this is the first that systematically reveals the complete phenol degradation mechanism by vetiver plantlets in real aerated wastewater.

Potential of Vetiveria zizanoides L. Nash for phytoremediation of plutonium ((239)Pu): Chelate assisted uptake and translocation

Plants have demonstrated a great potential to remove toxic elements from soils and solutions and been successfully used for phytoremediation of important radionuclides. Uptake potential of vetiver plants (V. zizanoides) for the remediation of (239)Pu in hydroponic and soil conditions was studied in the present work. High efficiency of V. zizanoides for the removal of (239)Pu was recorded with 66.2% being removed from the hydroponic solution after 30 days. However, remediation of (239)Pu from soil was limited. Remediation of (239)Pu from soil was increased with the addition of chelating agents citric acid (CA) and diethylenetriaminepentaacetic acid (DTPA). Accumulation of (239)Pu was recorded higher in roots than shoots, however its translocation from roots to shoots increased in the presence of chelators in hydroponic as well as soil conditions. DTPA was found more effective than CA showing higher translocation index (TI). Increase in TI was observed 8 and 6 times in the solution and soil respectively when plants were exposed to (239)Pu-DTPA in comparison to only (239)Pu. The present study demonstrates that V. zizanoides plant is a potential plant for phytoremediation of (239)Pu.