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  • Author or Editor: Eun Ha Yoo x
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Begonia maculata, Ardisia crenata, and Ardisia japonica plants exposed to 3.5 ppm toluene in air for 12 h displayed a pronounced stimulation (358%, 318%, and 252%, respectively) in subsequent toluene removal potential. The duration of the stimulation effect, monitored over 3 weeks, was short-lived decaying to prestimulation levels within 1 to 7 days depending on species. Elevated phytoremediation rate was dependent on the continued presence of toluene. The rapid rate of increase in phytoremediation and subsequent decay points toward a response mediated by changes in gene expression by the plant, microorganisms within the media, or both rather than an alteration in microbe population. A better understanding of the stimulation response may facilitate the use of plants for indoor air remediation in homes and offices.

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We investigated the interspecific relationships and intraspecific variations in the genus Corylopsis using RAPD and single nucleotide polymorphism (SNP) in the internal transcribed spacer1(ITS1), 5.8S ribosomal RNA gene specific in C. glabrescens Franch. & Sav. Differences in species identification between morphological characteristics and RAPD result were noticed in some accessions. All C. glabrescens, C. coreana Uyeki, and C. glabrescens f. gotoana (Makino) T. Yamanaka accessions clustered in one major group. However, they could be divided into five subgroups that are not related to the geographical origins. For example, C. coreana accessions from Korea were clustered with C. glabrescens from Japan. Although grouping based on SNP data does not agree with that by RAPD markers, it revealed the limitation in identification and classification of the genus due to high intraspecific variations in SNP. At SNP positions 464, 465, 466, 467, and 496, most accessions of C. glabrescens and C. coreana have C, G, A, A, and T, respectively. In both analyses, C. glabrescens, C. coreana, and C. glabrescens f. gotoana Japan are closely related and this suggests that nomenclature for these three species should be discussed. Although ITS1 5.8S ribosomal RNA gene can not be used for identification at a subspecies level of C. glabrescens, it proved to be useful to differentiate C. sinensisfrom C. sinensis var. calvescens. It is suggested to use C. glabrescens f. gotoana or C. glabrescens f. coreana rather than using C. coreana.

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The contribution of aerial plant parts versus the root zone to the removal of volatile formaldehyde by potted Fatsia japonica Decne. & Planch. and Ficus benjamina L. plants was assessed during the day and night. The removal capacity of the entire plant, aerial plant parts, and root zone was determined by exposing the relevant parts to gaseous formaldehyde (2 μL·L−1) in airtight chambers (1.0 m3) constructed of inert materials. The rate of formaldehyde removal was initially rapid but decreased as the internal concentration diminished in the chamber. To compare the removal efficiency between species and plant parts, the time interval required to reach 50% of the initial concentration was determined (96 and 123 min for entire plants of F. japonica and F. benjamina, respectively). In both species, the aerial plant parts reduced the formaldehyde concentration during the day but removed little during the night. However, the root zone eliminated a substantial amount of formaldehyde during the day and night. The ratio of formaldehyde removal by aerial plant parts versus the root zone was similar for both species, at ≈1:1 during the day and 1:11 at night. The effectiveness of the root zone in formaldehyde removal was due primarily to microorganisms and roots (≈90%); only about 10% was due to adsorption by the growing medium. The results indicate that the root zone is a major contributor to the removal of formaldehyde. A better understanding of formaldehyde metabolism by root zone microflora should facilitate maximizing the phytoremediation efficiency of indoor plants.

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Changes in phytoremediation efficiency after repeated exposures (three) to toluene (1.3 ppm) were assessed in 26 species and two additional cultivars of indoor plants. There was a rapid increase in toluene removal efficiency in 27 of the 28 crops with the greatest increase between the first and second exposure (i.e., after 3 days). The increase in efficiency between the first and third exposure ranged from 378 μg·m−3·h−1·m−2 leaf area in Pinus densiflora to –16.6 in Salvia elegans with a mean of 156 for all crops. Percent change ranged from 614 (Pittosporum tobira) to –8 (Salvia elegans) but was not necessarily indicative of phytoremediation value of a species. Rapid changes in phytoremediation efficiency in response to exposure to toluene appear to be widespread in plants and may be the result of an effect on gene expression in the plant and/or certain soil microbes or changes in the population density of toluene-metabolizing microbes. Increasing toluene removal efficiency is advantageous and as a consequence, a better understanding of the mechanism(s) operative may improve use of the response for practical applications.

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The efficiency of volatile formaldehyde removal was assessed in 86 species of plants representing five general classes (ferns, woody foliage plants, herbaceous foliage plants, Korean native plants, and herbs). Phytoremediation potential was assessed by exposing the plants to gaseous formaldehyde (2.0 μL·L−1) in airtight chambers (1.0 m3) constructed of inert materials and measuring the rate of removal. Osmunda japonica, Selaginella tamariscina, Davallia mariesii, Polypodium formosanum, Psidium guajava, Lavandula spp., Pteris dispar, Pteris multifida, and Pelargonium spp. were the most effective species tested, removing more than 1.87 μg·m−3·cm−2 over 5 h. Ferns had the highest formaldehyde removal efficiency of the classes of plants tested with O. japonica the most effective of the 86 species (i.e., 6.64 μg·m−3·cm−2 leaf area over 5 h). The most effective species in individual classes were: ferns—Osmunda japonica, Selaginella tamariscina, and Davallia mariesii; woody foliage plants—Psidium guajava, Rhapis excels, and Zamia pumila; herbaceous foliage plants—Chlorophytum bichetii, Dieffenbachia ‘Marianne’, Tillandsia cyanea, and Anthurium andraeanum; Korean native plants—Nandina domestica; and herbs—Lavandula spp., Pelargonium spp., and Rosmarinus officinalis. The species were separated into three general groups based on their formaldehyde removal efficiency: excellent (greater than 1.2 μg·m−3 formaldehyde per cm2 of leaf area over 5 h), intermediate (1.2 or less to 0.6), and poor (less than 0.6). Species classified as excellent are considered viable phytoremediation candidates for homes and offices where volatile formaldehyde is a concern.

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