Enhanced phytoremediation of atrazine-contaminated soil by vetiver (Chrysopogon zizanioides L.) and associated bacteria.

The intensive and long-term use of atrazine (ATZ) has led to the contamination of agricultural soils and non-target organisms, posing a series of threats to human health through the transmission of the food chain. In this study, a 60-day greenhouse pot experiment was carried out to explore the phytoremediation by Chrysopogon zizanioides L. (vetiver). The uptake, accumulation, distribution, and removal of ATZ were investigated, and the degradation mechanisms were elucidated. The results showed that the growth of vetiver was inhibited in the first 10 days of the incubation; subsequently, the plant recovered rapidly with time going. Vetiver grass was capable of taking up ATZ from the soil, with root concentration factor ranging from 2.36 to 15.55, and translocating to the shoots, with shoot concentration factor ranging from 7.51 to 17.52. The dissipation of ATZ in the rhizosphere soil (97.51%) was significantly higher than that in the vetiver-unplanted soil (85.14%) at day 60. Metabolites were identified as hydroxyatrazine (HA), deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA) in the samples of the shoots and roots of vetiver as well as the soils treated with ATZ. HA, DEA, DIA, and DDA were reported first time as metabolites of ATZ in shoots and roots of vetiver grown in soil. The presence of vetiver changed the formation and distribution of the dealkylated products in the rhizosphere soil, which remarkably enhanced the occurrence of DEA, DIA, and DDA. Arthrobacter, Bradyrhizobium, Nocardioides, and Rhodococcus were the major atrazine-degrading bacterial genera, which might be responsible for ATZ degradation in the rhizosphere soil. Our findings suggested that vetiver grass can significantly promote ATZ degradation in the soil, and it could be a strategy for remediation of the atrazine-contaminated agricultural soil.

Removal of atrazine from submerged soil using vetiver grass (Chrysopogon zizanioides L.).

The long-term widespread application of atrazine poses significant threats to the eco-environment and human health. To investigate the potential of vetiver (Chrysopogon zizanioides L.) for phytoremediation of the environmental media contaminated by atrazine, an indoor incubation experiment was conducted in submerged soil over 30 days. Results showed that the chlorophyll level of the vetiver was not significantly affected by exposure to atrazine. Vetiver could take up and accumulate atrazine from submerged soil and peaked around the 20th day with a concentration of 1.0 mg kg-1 in leaf. The metabolites Hydroxyatrazine (HA), deethylatrazine (DEA), Deisopropylatrazine (DIA), and didealkylatrazine (DDA) were detected in the leaf on the 30th day, indicating vetiver could degrade atrazine inside the leaf tissue. The atrazine removal rate in the vetiver planted and unplanted jars were 69.72 and 60.29%, respectively, indicating that 9.43% higher atrazine removal was achieved in the presence of vetiver (p < 0.05). The atrazine dissipation in the submerged soil followed first-order kinetics, the degradation constant was 0.066, and the half-life of atrazine dissipation was shortened by 6.86 days in the presence of vetiver. The present study suggests that vetiver can take up atrazine from submerged soil and accumulate in the leaf, which could then degrade in the leaf.Novelty statement: Although the fate of atrazine in agricultural soils has been extensively investigated through various experiments, little is known about the effect of vetiver grass on atrazine dissipation from submerged soil. With the identification of soil-leaf transportation and four metabolites in vetiver leaf and soils, significantly accelerated atrazine dissipation from the submerged soil was achieved in the presence of vetiver. Particularly, the formation of less toxic dealkylated products in the leaf indicated vetiver is a promising grass for atrazine removal from submerged soil.

Complete Chloroplast Genomes and Comparative Analyses of Three Ornamental Impatiens Species.

Impatiens L., the largest genus in the family Balsaminaceae with approximately 1,000 species, is a controversial genus. Due to the conflict of morphological features and insufficient genomic resources, the studies of systematic evolution and understanding of taxonomic identification are considered to be very limited. Hence, we have sequenced the complete chloroplast genomes of three ornamental species (Impatiens balsamina, I. hawkeri, and I. walleriana), and compared them with previously published wild species data. We performed a detailed comparison of a highly similar basic structure, size, GC content, gene number, order, and functional array among them. Similarly, most divergent genes were detected from previous work in the literature. The mutational regions containing highly variable nucleotide hotspots were identified and may be used as potential markers for species identification and taxonomy. Furthermore, using whole chloroplast genome data to analysis the phylogenetic relationship of the Balsaminaceae species, we found that they were all part of a single clade. The three phenotypically different ornamental species were clustered together, suggesting that they were very likely to be closely related. We achieved and characterized the plastid genome structure, identified the divergence hotspots, and determined the phylogenetic and taxonomic positions of the three cultivated species in the Impatiens genus. The results may show that the chloroplast genome can be used to solve phylogenetic problems in or between the Impatiens genus and also provide genomic resources for the study of the Balsaminaceae family's systematics and evolution.