Particulate matter and volatile organic compound phytoremediation by perennial plants: Affecting factors and plant stress response.

Air pollution by particulate matter (PM) and volatile organic compounds (VOCs) is a major global issue. Many technologies have been developed to address this problem. Phytoremediation is one possible technology to remediate these air pollutants, and a few studies have investigated the application of this technology to reduce PM and VOCs in a mixture of pollutants. This study aimed to screen plant species capable of PM and VOC phytoremediation and identify plant physiology factors to be used as criteria for plant selection for PM and VOC phytoremediation. Wrightia religiosa removed PM and VOCs. In addition, the relative water content in the plant and ethanol soluble wax showed positive relationships with PM and VOC phytoremediation, with a high correlation coefficient. For plant stress responses, several plant species maintained and/or increased the relative water content after short-term exposure to PM and VOCs. In addition, based on proteomic analysis, most of the proteins in W. religiosa leaves related to photosystems I and II were significantly reduced by PM2.5. When a high water content was achieved in W. religiosa (80% soil humidity), W. religiosa can effectively remove PM. The results suggested that PM can reduce plant photosynthesis. In addition, plants might require a high water supply to maintain their health under PM and VOC stress.

Euphorbia milii-Endophytic Bacteria Interactions Affect Hormonal Levels of the Native Host Differently Under Various Airborne Pollutants.

This study was conducted to assess the effect of plant-native endophytic bacteria interactions on indole-3-acetic acid (IAA), ethylene levels, and hormonal balance of Euphorbia milii under different airborne pollutants. IAA levels and airborne formaldehyde removal by E. milii enhanced when inoculated with endophytic isolates. However, one isolate, designated as root endophyte 4, with the highest levels of IAA production individually, declined gaseous formaldehyde removal of plant, since it disturbed hormonal balance of E. milii, leading to IAA levels higher than physiological concentrations, which stimulated ethylene biosynthesis and stomatal closure under light conditions. However, plant-root endophyte 4 interactions favored airborne benzene removal, since benzene was more phytotoxic and the plant needed more IAA to protect against benzene phytotoxicity. As trimethylamine (TMA) was not toxic, it did not affect plant-endophyte interactions. Therefore, IAA levels of root endophyte 4-inoculated E. milii was not significantly different from a noninoculated one. Under mixed-pollutant stress (formaldehyde, benzene, TMA), root endophyte 4-inoculated E. milii removed benzene at the lowest rate, since benzene was the most phytotoxic pollutant with the greatest molecular mass. However, TMA (with greater molecular mass) was removed faster than formaldehyde due to higher phytotoxicity of formaldehyde. Plant-endophyte interactions were affected differently under various airborne pollutants.

Uptake and degradation of trimethylamine by Euphorbia milii.

Trimethylamine (TMA) is a volatile organic compound which causes not only unpleasant odor but also health concerns to humans. The average emission of TMA from food and fishery industries is 20.60 parts per billion (ppb) and emission from the gas exhausters is even higher which reaches 370 parts per million (ppm). In order to select the best plant TMA removal agent, in this study, 13 plants were exposed to 100 ppm of TMA and the remaining TMA concentration in their system was analyzed by gas chromatography (GC). Furthermore, plant metabolites from the selected plant were identified by gas chromatography-mass spectrometry (GC-MS). The result showed that Euphorbia milii was the most superior plant for TMA removal and could absorb up to 90 % of TMA within 12 h. E. milii absorbed TMA via leaf and stem with 55 and 45 % uptake efficiency, respectively. Based on its stomatal movement during the exposure to TMA, it was implied that the plant switched the photosynthetic mode from crassulacean acid metabolism (CAM)-cycling to CAM and CAM-idling. The switching of photosynthetic mode might reduce the stomata role in TMA absorption. Fatty acids, alkanes, and fatty alcohols in the plant leaf wax were also found to contribute to TMA adsorption. Leaf wax, stomata, and other leaf constituents contributed 58, 6, and 36 %, respectively, of the total TMA absorption by the leaf. The analysis and identification of plant metabolites confirmed that TMA was degraded and mineralized by E. milii.