Synergistic mitigation of atrazine-induced oxidative stress on soybeans in black soil using biochar and Paenarthrobacter sp. AT5

Atrazine, a widely used herbicide in modern agriculture, can lead to soil contamination and adverse effects on specific crops. To address this, we investigated the efficacy of biochar loaded with Paenarthrobacter sp. AT5 (an atrazine-degrading bacterial strain) in mitigating atrazine's impact on soybeans in black soil. Bacterially loaded biochar (BBC) significantly enhanced atrazine removal rates in both unplanted and planted soil systems. Moreover, BBC application improved soybean biomass, photosynthetic pigments, and antioxidant systems while mitigating alterations in metabolite pathways induced by atrazine exposure. These findings demonstrate the effectiveness of BBC in reducing atrazine-induced oxidative stress on soybeans in black soil, highlighting its potential for sustainable agriculture.

Coinoculation of arbuscular mycorrhizal fungi and rhizobia stimulates atrazine dissipation by changing the atrazine-degrading bacterial community at the soil aggregate scale

As a potential low-cost and environmentally friendly strategy, bioremediation of herbicide polluted soil has attracted increasing attention. However, there is a lack of knowledge regarding the response of the atrazine-degrading bacterial community to coinoculation of arbuscular mycorrhizal (AM) fungi and rhizobia for atrazine dissipation. In this study, a pot experiment was conducted with AM fungi Glomus mosseae (AM), rhizobia Rhizobium trifolii TA-1 (R) and their coinoculation (AMR) with atrazine. In each treatment, the atrazine-degrading bacterial community of four soil size aggregates, namely large macroaggregates (LMa), small macroaggregates (SMa), microaggregates (Mia) and primary particles (P) were investigated. The results showed that the atrazine residue concentration was lowest in AMR, and that in LMa was also significantly lower than that in the other smaller aggregate sizes. Overall, inoculation, the aggregate fraction and their interaction had significant effects on soil TN, SOC, AP and pH. For the atrazine-degrading bacterial community, the Chao1 index increased with decreasing particle size, but the Shannon index decreased. Moreover, the abundances of the dominant atrazine-degrading bacterial genera Arthrobacter, Bacillus, Marmoricola and Nocardioides in the Mia and P particle size groups were greater than those in the LMa and SMa groups in each treatment. The bacterial communities in the Mia and P particle sizes in each treatment group were more complex. Therefore, coinoculation of AM fungi and rhizobia stimulated atrazine dissipation by changing the atrazine-degrading bacterial community, and the response of the atrazine-degrading bacterial community to each aggregate size varied depending on its distinct soil physicochemical properties.

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.

Occurrence, diversity and community structure of culturable atrazine degraders in industrial and agricultural soils exposed to the herbicide in Shandong Province, P.R. China

Background

Soil populations of bacteria rapidly degrading atrazine are critical to the environmental fate of the herbicide. An enrichment bias from the routine isolation procedure prevents studying the diversity of atrazine degraders. In the present work, we analyzed the occurrence, diversity and community structure of soil atrazine-degrading bacteria based on their direct isolation.

Methods

Atrazine-degrading bacteria were isolated by direct plating on a specially developed SM agar. The atrazine degradation genes trzN and atzABC were detected by multiplex PCR. The diversity of atrazine degraders was characterized by enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) genotyping followed by 16S rRNA gene phylogenetic analysis. The occurrence of atrazine-degrading bacteria was also assessed by conventional PCR targeting trzN and atzABC in soil DNA.

Results

A total of 116 atrazine-degrading isolates were recovered from bulk and rhizosphere soils sampled near an atrazine factory and from geographically distant maize fields. Fifteen genotypes were distinguished among 56 industrial isolates, with 13 of them representing eight phylogenetic groups of the genus Arthrobacter. The remaining two were closely related to Pseudomonas alcaliphila and Gulosibacter molinativorax and constituted major components of the atrazine-degrading community in the most heavily contaminated industrial plantless soil. All isolates from the adjacent sites inhabited by cogon grass or common reed were various Arthrobacter spp. with a strong prevalence of A. aurescens group. Only three genotypes were distinguished among 60 agricultural strains. Genetically similar Arthrobacter ureafaciens bacteria which occurred as minor inhabitants of cogon grass roots in the industrial soil were ubiquitous and predominant atrazine degraders in the maize rhizosphere. The other two genotypes represented two distant Nocardioides spp. that were specific to their geographic origins.

Conclusions

Direct plating on SM agar enabled rapid isolation of atrazine-degrading bacteria and analysis of their natural diversity in soil. The results obtained provided evidence that contaminated soils harbored communities of genetically distinct bacteria capable of individually degrading and utilizing atrazine. The community structures of culturable atrazine degraders were habitat-specific. Bacteria belonging to the genus Arthrobacter were the predominant degraders of atrazine in the plant rhizosphere.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0868-3) contains supplementary material, which is available to authorized users.