Wenchao Du

Interaction of metal oxide nanoparticles with higher terrestrial plants: Physiological and biochemical aspects.

Multiple applications of metal oxide nanoparticles (MONPs) could result in their accumulation in soil, threatening higher terrestrial plants. Several reports have shown the effects of MONPs on plants. In this review, we analyze the most recent reports about the physiological and biochemical responses of plants to stress imposed by MONPs. Findings demonstrate that MONPs may be taken up and accumulated in plant tissues causing adverse or beneficial effects on seed germination, seedling elongation, photosynthesis, antioxidative stress response, agronomic, and yield characteristics. Given the importance of determining the potential risks of MONPs on crops and other terrestrial higher plants, research questions about field long-term conditions, transgenernational phytotoxicity, genotype specific sensitivity, and combined pollution problems should be considered.

Physiological and Biochemical Changes Imposed by CeO2 Nanoparticles on Wheat: A Life Cycle Field Study

Interactions of nCeO2 with plants have been mostly evaluated at seedling stage and under controlled conditions. In this study, the effects of nCeO2 at 0 (control), 100 (low), and 400 (high) mg/kg were monitored for the entire life cycle (about 7 months) of wheat plants grown in a field lysimeter. Results showed that at high concentration nCeO2 decreased the chlorophyll content and increased catalase and superoxide dismutase activities, compared with control. Both concentrations changed root and leaf cell microstructures by agglomerating chromatin in nuclei, delaying flowering by 1 week, and reduced the size of starch grains in endosperm. Exposed to low concentration produced embryos with larger vacuoles, while exposure to high concentration reduced number of vacuoles, compared with control. There were no effects on the final biomass and yield, Ce concentration in shoots, as well as sugar and starch contents in grains, but grain protein increased by 24.8% and 32.6% at 100 and 400 mg/kg, respectively. Results suggest that more field life cycle studies are needed in order to better understand the effects of nCeO2 in crop plants.

Environmental fate of phenanthrene in lysimeter planted with wheat and rice in rotation

An outdoor lysimeter experiment was conducted to investigate the fate of 14C-labeled phenanthrene in the soil planted with wheat and rice in rotation. Results showed that applied 14C-activity in the soil decreased mainly through gaseous losses; 67.5% of it evaporated as 14CO2. After the rice harvest, the surface soil retained 21.7% of applied 14C-activity, of which 92.4% remained in nonextractable soil residues. The 14C-activities found in deeper layers of the soil column indicated vertical migration of phenanthrene or metabolites. Furthermore, the 14C-activities detected in five organs of mature wheat or rice decreased in the order: roots > leaves > shells>stems > grains. The vertical migration and its accumulation by grains suggest that PAHs in field have adverse effects on the security of groundwater and food.

Elevated CO2 levels increase the toxicity of ZnO nanoparticles to goldfish (Carassius auratus) in a water-sediment ecosystem.

Concerns about the environmental safety of metal-based nanoparticles (MNPs) in aquatic ecosystems are increasing. Simultaneously, elevated atmospheric CO2 levels are a serious problem worldwide, making it possible for the combined exposure of MNPs and elevated CO2 to the ecosystem. Here we studied the toxicity of nZnO to goldfish in a water-sediment ecosystem using open-top chambers flushed with ambient (400±10μL/L) or elevated (600±10μL/L) CO2 for 30days. We measured the content of Zn in suspension and fish, and analyzed physiological and biochemical changes in fish tissues. Results showed that elevated CO2 increased the Zn content in suspension by reducing the pH value of water and consequently enhanced the bioavailability and toxicity of nZnO. Elevated CO2 led to higher accumulation of Zn in fish tissues (increased by 43.3%, 86.4% and 22.5% in liver, brain and muscle, respectively) when compared to ambient. Elevated CO2 also intensified the oxidative damage to fish induced by nZnO, resulting in higher ROS intensity, greater contents of MDA and MT and lower GSH content in liver and brain. Our results suggest that more studies in natural ecosystems are needed to better understand the fate and toxicity of nanoparticles in future CO2 levels.

Fate and ecological effects of decabromodiphenyl ether in a field lysimeter.

Flame-retardant polybrominated diphenyl ethers (PBDEs) are environmental contaminants. Deca-BDE is increasingly used commercially, but little is known about the long-term fate and impact of its major component, decabromodiphenyl ether (BDE-209), on the soil environment. In this study, we investigated the fate and ecological effect of BDE-209 over 4 years in outdoor lysimeters in a field planted with a rice-wheat rotation. BDE-209 and six lower-brominated PBDEs (BDE-28, -47, -99, -153, -154, and -183) were detected in soil layers of the test lysimeter. We calculated an average BDE-209 migration rate of 1.54 mg·m(-2)·yr(-1). In samples collected in May 2008, November 2008, November 2009, November 2010, and November 2011, 95.5%, 94.3%, 108.1%, 33.8%, and 35.5% of the spiked BDE-209 were recovered, respectively. We predicted the major pathway for debromination of BDE-209 in soil to be: BDE-209→BDE-183→BDE-153/BDE-154→BDE-99→BDE-47→BDE-28. In plants, BDE-209 and seven lower-brominated PBDEs (BDE-28, -47, -99, -100, -153, -154, and -183) were detected. BDE-100 was mainly derived from the debromination of BDE-154 in plants, but sources of other lower-brominated PBDEs were still difficult to determine. In soils containing BDE-209 for 4 years, soil urease activity increased, and soil protease activity slightly decreased. Our results provide important insights for understanding the behavior of BDE-209 in agricultural soils.

Elevated CO2 levels modify TiO2 nanoparticle effects on rice and soil microbial communities

Evidence suggests that CO2 modifies the behavior of nanomaterials. Thus, in a few decades, plants might be exposed to additional stress if atmospheric levels of CO2 and the environmental burden of nanomaterials increase at the current pace. Here, we used a full-size free-air CO2 enrichment (FACE) system in farm fields to investigate the effect of elevated CO2 levels on phytotoxicity and microbial toxicity of nTiO2 (0, 50, and 200mgkg-1) in a paddy soil system. Results show that nTiO2 did not induce visible signs of toxicity in rice plants cultivated at the ambient CO2 level (370μmolmol-1), but under the high CO2 concentration (570μmolmol-1) nTiO2 significantly reduced rice biomass by 17.9% and 22.1% at 50mgkg-1 and 200mgkg-1, respectively, and grain yield by 20.8% and 44.1% at 50mgkg-1 and 200mgkg-1, respectively. In addition, at the high CO2 concentration, nTiO2 at 200mgkg-1 increased accumulation of Ca, Mg, Mn, P, Zn, and Ti by 22.5%, 16.8%, 29.1%, 7.4%, 15.7% and 8.6%, respectively, but reduced fat and total sugar by 11.2% and 25.5%, respectively, in grains. Such conditions also changed the functional composition of soil microbial communities, alerting specific phyla of bacteria and the diversity and richness of protista. Overall, this study suggests that increases in CO2 levels would modify the effects of nTiO2 on the nutritional quality of crops and function of soil microbial communities, with unknown implications for future economics and human health.

Differential effects of copper nanoparticles/microparticles in agronomic and physiological parameters of oregano (Origanum vulgare)

The effects of metallic copper nanoparticles (nCu) in plants are not well understood. In this study, soil grown oregano (Origanum vulgare) was exposed for 60days to nCu and Cu microparticles (μCu) at 0-200mgCu/kg. At harvest, Cu accumulation, biomass production, nutrient composition, and Cu fractions in soil were measured. Except for μCu at 50mg/kg, both nCu and μCu increased root Cu (28.4-116.0%) and shoot Cu (83.0-163.0% and 225.4-652.5%, respectively), compared with control. Copper accumulation from μCu increased as the external μCu increased. nCu and μCu did not affect shoot length, malondialdehyde, or chlorophyll, but increased water content (6.9-12.5%) and reduced shoot biomass (21.6-58.5%), compared with control. In addition, at 50mg/kg, μCu decreased root biomass and length (48.6% and 20.5%, respectively) and water content (1.8% and 3.9% at 100 and 200mg/kg, respectively). All treatments modified root and shoot Ca, Fe, Mg, and Mn (p≤0.05). Additionally, all Cu treatments decreased starch (33.9-58.5%), total sugar (39.5-55.7%), and reducing sugar (13.6-33.9%) in leaves. Results showed that metallic Cu nanoparticles/microparticles affected agronomical and physiological parameters in oregano, which could impact human nutrition. However, smaller size particles do not necessarily imply greater toxicity.

Effects of the exposure of TiO 2 nanoparticles on basil ( Ocimum basilicum ) for two generations

There is a lack of information about the transgenerational effects of titanium dioxide nanoparticles (nano-TiO2) in plants. This study aimed to evaluate the impacts of successive exposure of nano-TiO2 with different surface properties to basil (Ocimum basilicum). Seeds from plants exposed or re-exposed to pristine, hydrophobic, or hydrophilic nano-TiO2 were cultivated for 65 days in soil unamended or amended with 750 mg·kg-1 of the respective particles. Plant growth, concentration of titanium and essential elements, as well as content of carbohydrates and chlorophyll were evaluated. There were no differences on Ti concentration in roots of plants sequentially exposed to pristine or hydrophobic nano-TiO2, or in roots of plants exposed to the corresponding particle, only in the second cycle. However, sequential exposure to hydrophilic particles resulted in 65.2% less Ti in roots, compared to roots of plants exposed the same particles, only in the second cycle. The Ti concentrations in shoots were similar in all treatments. On the other hand, pristine and hydrophilic particles reduced Mg in root by 115% and 81%, respectively, while pristine and hydrophobic particles reduced Ni in shoot by 84% and 75%, respectively, compared to unexposed plants in both cycles. Sequential exposure to pristine nano-TiO2 increased stomatal conductance (214%, p ≤ 0.10), compared to plants that were never exposed. Hydrophobic and hydrophilic nano-TiO2 reduced chlorophyll b (52%) and total chlorophyll (30%) but increased total sugar (186%) and reducing sugar (145%), compared to unexposed plants in both cycles. Sequential exposure to hydrophobic or hydrophilic nano-TiO2 resulted in more adverse effects on photosynthesis but in positive effects on plant growth, compared to pristine nano-TiO2.

Combination of Elevated CO2 Levels and Soil Contaminants’ Stress in Wheat and Rice

Elevated CO2 levels and the increase in heavy metals in soils through pollution are serious problems worldwide. Whether elevated CO2 levels will affect plants grown in heavy-metal-polluted soil and thereby influence food quality and safety is not clear. Using a free-air CO2 enrichment (FACE) system, we investigated the impacts of elevated atmospheric CO2 on the concentrations of copper (Cu) or cadmium (Cd) in rice and wheat grown in soil with different concentrations of the metals in the soil. In this 2-year study, the interactive effects of CO2 on Cu and Cd uptake in rice and wheat leaves were examined. The activities of antioxidant enzymes—catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and superoxide dismutase (SOD)—in rice and wheat leaves were used to assess the combined stress. Elevated CO2 levels led to lower Cu concentrations and higher Cd concentrations in shoots and grain of both rice and wheat grown in the respective contaminated soil. Elevated CO2 levels lowered the pH of the soil and led to changes in the availability of Cu and Cd in the soil. This study indicates that elevated CO2 alters the distribution of contaminant elements in soil and plants, thereby impacting food quality and safety.

Elevated temperature and CO 2 affect responses of European aspen ( Populus tremula ) to soil pyrene contamination

High northern latitudes are climatic sensitive areas, and are also regions to which polycyclic aromatic hydrocarbons (PAHs) easily transport and accumulate with potential risk to natural ecosystems. However, the effect of PAHs on northern woody plant growth and defense under climate change is very little studied. Here, we conducted a unique experiment in greenhouses to investigate sex-related responses of the dioecious Populus tremula to pyrene (50mgkg-1) and residue of pyrene in soils under ambient and elevated temperature (+1.8°C on average) and CO2 (740ppm). Pyrene decreased stem biomass and leaf area by 9% and 6%, respectively under ambient conditions, and the reduction of leaf area was more severe under elevated temperature (38%), elevated CO2 (37%), and combined T+CO2 (42%). Other growth parameters were unchanged by pyrene. Pyrene did not affect the concentration of leaf total phenolics under ambient conditions, but increased it by 16%, 1%, and 20% compared to controls under elevated temperature, elevated CO2, and T+CO2, respectively. Pyrene had only minor sex-specific effects on plant growth and phenolics. The concentration of residual pyrene in pyrene-spiked soils was higher under elevated CO2 than under ambient, elevated temperature, and combined T+CO2. The results suggest that both sexes of P. tremula have the capacity to regulate growth and metabolism to adjust to the stress of the tested pyrene contamination under elevated temperature and CO2, but potential risk of pyrene to plants still exists in the future changing climate.