The density-dependence of terrestrial plant–plant interactions in the presence of toxins has previously been explored using biodegradable compounds. We exposed barley and lettuce to four copper concentrations at four stand densities. We hypothesized that toxin effects would decrease and Cu uptake would increase at increasing plant densities. We analyzed toxin effects by (a) comparing plant biomasses and (b) using a recent regression model that has a separate parameter for the interaction of resource competition and toxin interference. Plant response to Cu was density-dependent in both experiments. Total Cu uptake by barley increased and the dose per plant decreased as plant density increased. This study is the first to demonstrate that plant density mediates plant response to metals in soil in a predictable way. This highlights the need to explore the mechanisms for and consequences of these effects, and to integrate the use of several plant densities into standard ecotoxicological testing.

We investigated the effects of arsenic species on As accumulation, plant growth and rhizospheric changes in As−hyperaccumulator Pteris vittata (PV). PV was grown for 60−d in a soil spiked with 200 mg kg−1 arsenate (AsV−soil) or arsenite (AsIII−soil). Diffusive gradients in thin−films technique (DGT) were used to monitor As uptake by PV. Interestingly AsIII−soil produced the highest PV biomass at 8.6 g plant−1, 27% and 46% greater than AsV−soil and the control. Biomass increase was associated with As−induced P uptake by PV. Although AsIII was oxidized to AsV during the experiment, As species impacted As accumulation by PV, with 17.5% more As in AsIII−soil than AsV−soil (36 vs. 31 mg plant−1). As concentration in PV roots was 30% higher in AsV−soil whereas As concentration in PV fronds was 7.9% greater in AsIII−soil, suggesting more rapid translocation of AsIII than AsV. These findings were important to understand the mechanisms of As uptake, accumulation and translocation by PV.

With the aim of investigating the effects of carbonaceous sorbent amendment on plant health and end point contaminant bioavailability, plant experiments were set up to grow maize (Zea mays) in soil contaminated with polycyclic aromatic hydrocarbons (PAHs) and metals. Maize and pine derived biochars, as well as a commercial grade activated carbon, were used as amendments. Plant growth characteristics, such as chlorophyll content and shoot to root biomass, improved with sorbent amendment to varying extents and contaminant uptake to shoots was consistently reduced in amended soils. By further defining the conditions in which sorbent amended soils successfully reduce contaminant bioavailability and improve plant growth, this work will inform field scale remediation efforts.

We investigated impacts of Macondo MC252 oil from the Deepwater Horizon (DWH) spill on the common reed Phragmites australis (Cav.) Trin. ex Steud., a dominant species of the Mississippi River Delta. In greenhouse experiments, we simulated the most common DWH oiling scenarios by applying weathered and emulsified Macondo oil to aboveground shoots at varying degrees of coverage (0–100%) or directly to marsh soil at different dosages (0–16Lm−2). P. australis exhibited strong resistance to negative impacts when oil was applied to shoots alone, while reductions in above- and belowground plant growth were apparent when oil was applied to the soil or with repeated shoot-oiling. Although soil-oiling compromised plant function, mortality of P. australis did not occur. Our results demonstrate that P. australis has a high tolerance to weathered and emulsified Macondo oil, and that mode of exposure (aboveground versus belowground) was a primary determinant of impact severity.

The present study reports the remediation of radiocesium-137 (¹³⁷Cs) using napiergrass in Cs-contaminated soils of Fukushima Prefecture. Two field experiments were performed to examine the remediation effects in two different land-use soils (lowland and upland soils) using two different cutting frequencies (cut once or twice a year). Plant growth in the upland soil was significantly greater than that in the lowland soil. The¹³⁷Cs concentration (Bq kg⁻¹dry weight basis) in the aboveground parts and total Cs-removal ratio (CR) in the upland soil were also significantly higher than those in the lowland soil. In the lowland soil, cutting twice a year [at 12 and 24 weeks after transplanting (WAT)] was more effective for CR (P < 0.01) than cutting once a year (18 WAT); however, there was no significant difference of CR related to cutting difference in the upland soil as a result of the shading effect on the plants at second cutting. In the present study, aboveground dry matter weight was highly correlated with CR in both fields. Given the possibility to increase plant number per unit of land to increase aboveground biomass per unit of land, the potential Cs remediation effect could be much greater in a wide range of Cs-contaminated soils than the potential of napiergrass for Cs uptake demonstrated in the present study.

Cadmium (Cd) is a toxic and nonessential element. Because of its toxicity, Cd soil contamination is a major environmental risk to living organisms. Several studies have reported on the successful use of biochar to immobilize Cd in soil as it reduces Cd accumulation in plant parts. This research reports on the contrasting effect of biochar on enhancing Cd uptake by plants. A cassava stem biochar produced through low-temperature pyrolysis was applied to natural Cd-contaminated soil that also had a high zinc (Zn) concentration. Vigna radiata L. (a green bean) was grown in treatments receiving three biochar rates, i.e., 5, 10, and 15 %, respectively. The results showed that the 10 % biochar-amended soil had a positive effect on promoting plant growth and seed yield. Unfortunately, 15 % biochar-amended soil caused an adverse effect to plant growth. Cadmium uptake by plants increased with increasing biochar application rate. Zinc uptake by plants tended to decrease with biochar application. Cadmium and Zn bioavailability in soil was significantly reduced with an increasing biochar application rate. The results also showed that the biochar-amended soil could be an alternative and cost-effective method to promote plant growth and decrease Cd mobility in soil. The ratio of Cd concentration in plant root to soil was higher than 1, while the translocation factor from root to shoot was less than 1. These results indicate that the cultivation of V. radiata L. coupled with biochar application is an appropriate method to enhance Cd phytostabilization efficiency of V. radiata L. in Cd-polluted sites.

The potential use of the arsenic-tolerant woody leguminous species Anadenanthera peregrina (L) Spegazzini for rehabilitating arsenic (As)-contaminated areas was studied. In an As (539.33 mg/kg)-contaminated soil experiment, plants were able to accumulate arsenic in their roots with a low transfer index to the shoot. Inoculation with arbuscular mycorrhizal fungi (AMF) amplified this behavior and improved both biomass production and the phosphorus concentration in the shoot. AMF inoculation not only improved A. peregrina plant growth but also protected the shoot against As toxicity. Aside from the AMF inoculation, the addition of organic matter reduced the soil pH, thus improving the ability of the roots to accumulate arsenic. The majority (81 %) of the variations in As accumulation in A. peregrina roots were explained by the effects of the organic matter and soil pH as well as AMF treatments, as found by a principal component analysis. A. peregrina promoted phytostabilization through As root sequestration. Therefore, A. peregrina plants inoculated with AMF in the presence of organic matter are recommended to rehabilitate degraded areas of soil contaminated with arsenic.

Phytoremediation can be assisted by microorganisms, which promote plant growth and increase heavy metal availability in soil. In this study, we aimed at evaluating the effect of two plant growth-promoting bacteria (PGPB) on phytoextraction of copper (Cu) by maize. We chose the strains based on their ability to synthesize indole compounds, produce siderophores, solubilize phosphorus, and increase soil conductivity and extractable Cu in soil. Then, in glasshouse experiments, we assessed their ability to increase biomass, chlorophyll content, and Cu extraction by maize. Results showed that Acinetobacter sp. RG30 and Pseudomonas putida GN04 were overall the most active strains to synthesize indole, produce siderophores, and solubilize phosphorus, and hence selected for further studies. Also, both were able to significantly increase soil conductivity and release Cu from soil compared to control. Glasshouse experiments showed that Cu had a negative effect on plant growth, but inoculation with bacteria promoted plant growth and chlorophyll content in its presence (p < 0.05). Notably, the effect of inoculation on plant growth was larger on contaminated than on uncontaminated soil, which suggests an overall bacterial effect for alleviation of stress caused by Cu. Inoculation with RG30 or GN04 improved Cu extraction by maize (p < 0.05); interestingly, co-inoculation led to the highest accumulation (200 μg Cu/g plant dry weight). We conclude, therefore, that inoculation with RG30 and GN04 improves metal extraction by increasing plant growth, fitness, and availability of minerals in soil, which represents an important tool for the improvement of phytoextraction processes in polluted environments.

A mesocosm experiment was established to evaluate the effect of two organic wastes: fermented sugar beet residue (SBR) and urban waste compost on the stimulation of plant growth, phytoaccumulation of heavy metals (HM) and soil biological quality and their possible use in phytostabilization tasks with native (Piptatherum miliaceum, Retama sphaerocarpa, Bituminaria bituminosa, Coronilla juncea and Anthyllis cytisoides) and non-native (Lolium perenne) plants in a heavy metal-contaminated semiarid soil. Except R. sphaerocarpa, SBR increased the contents of shoot N, P and K and shoot biomass of all plants. The percentage of mycorrhizal colonization was not affected by the organic amendments. The highest increase in dehydrogenase and β-glucosidase activities was recorded in SBR-amended P. miliaceum. SBR decreased toxic levels of HM in shoot of P. miliaceum, mainly decreasing Fe and Pb uptake to plants. This study pointed out that the SBR was the most effective amendment for enhancing the plant performance and for improving soil quality. The combination of SBR and P. miliaceum can be regarded the most effective strategy for being employed in phytostabilization projects of this contaminated site.

The low bioavailability of Pb and low number of Pb-tolerant plant species represent an important limitation for Pb phytoextraction. It was recently suggested that halophyte plant species may be a promising material for this purpose, especially in polluted salt areas while Pb mobility may be improved by synthetic chelating agents. This study aims to evaluate Pb extraction by the halophyte Sesuvium portulacastrum in relation to the impact of EDTA application. Seedling were cultivated during 60 days on Pb artificially contaminated soil (200, 400, and 800 ppm Pb) in the presence or in the absence of EDTA (3 g kg⁻¹soil). Results showed that upon to 400 ppm, Pb had no impact on plant growth. However, exogenous Pb induce a decrease in shoot K⁺while it increased shoot Mg²⁺and had no impact on shoot Ca²⁺concentrations. Lead concentration in the shoots increased with increasing external Pb doses reaching 1,390 ppm in the presence of 800 ppm lead in soil. EDTA addition had no effect on plant growth but strongly increased Pb accumulation in the shoot which increased from 1,390 ppm in the absence of EDTA to 3,772 ppm in EDTA-amended plants exposed to 800 ppm exogenous Pb. Both Pb absorption and translocation from roots to shoots were significantly enhanced by EDTA application, leading to an increase in the total amounts of extracted Pb per plant. These data suggest that S. portulacastrum is very promising species for decontamination of Pb²⁺-contaminated soil and that its phytoextraction potential was significantly enhanced by addition of EDTA to the polluted soil.