Abstract
Although plants of the genus Pennisetum can accelerate the removal of atrazine from its rhizosphere, the roles played by this plant in adjusting the soil environment and soil microorganism properties that might contribute to pollutant removal are incompletely understood. We selected Pennisetum americanum (L.) K. Schum (P. americanum) as the test plant and investigated the interaction between P. americanum and atrazine-contaminated soil, focusing on the adjustment of the soil biochemical properties as well as bacterial functional and community diversity in the rhizosphere using Biolog EcoPlates and high-throughput sequencing of the 16S rRNA gene. The results demonstrate that the rhizosphere soil of P. americanum exhibited higher catalase activity, urease activity and water soluble organic carbon (WSOC) content, as well as a suitable pH for microorganisms after a 28-day incubation. The bacterial functional diversity indices (Shannon and McIntosh) for rhizosphere soil were 3.17 ± 0.04 and 6.43 ± 0.86 respectively, while these indices for non-rhizosphere soil were 2.95 ± 0.06 and 3.98 ± 0.27. Thus, bacteria in the P. americanum rhizosphere exhibited better carbon substrate utilization than non-rhizosphere bacteria. Though atrazine decreased the richness of the soil bacterial community, rhizosphere soil had higher bacterial community traits. For example, the Shannon diversity indices for rhizosphere and non-rhizosphere soil were 5.821 and 5.670 respectively. Meanwhile, some bacteria, such as those of the genera Paenibacillus, Rhizobium, Sphingobium, and Mycoplana, which facilitate soil nutrient cycling or organic pollutants degradation, were only found in rhizosphere soil after a 28-day remediation. Moreover, redundancy analysis suggests that the soil biochemical properties that were adjusted by the test plant exhibited correlations with the bacterial community composition and functional diversity. These results suggest that the soil environment and bacterial properties could be adjusted by P. americanum during phytoremediation of atrazine-contaminated soil.
Highlights
Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is one of the most widely used herbicides in agriculture
To illustrate the regulatory role of the P. americanum rhizosphere on bacterial functional diversity and the bacterial community structure of atrazine-contaminated soil, three treatments were set up: (1) soil without any addition of atrazine or P. americanum, which served as the control treatment (CK); (2) soil without planting of P. americanum but with addition of 20 mg kg−1 atrazine, which served as pollution treatment (PT); (3) soil with planting of P. americanum and addition of 20 mg kg−1 atrazine as phytoremediation treatment (RT)
Pennisetum americanum planted in atrazine-contaminated soil shaped the bacterial communities and enhanced the bacterial functional diversity of the rhizosphere by re-shaping the soil physicochemical properties, such as catalase activity, urease activity, water-soluble organic carbon (WSOC) and pH, to be more suitable to soil microorganisms
Summary
Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is one of the most widely used herbicides in agriculture. Though atrazine has been proved highly persistent in the environment with the reported half-life ranges between 10 and 5824 days (Salazar-Ledesma et al, 2018), it could be metabolized in environment according to microbiological degradation and some kinds of physicochemical process (Sun et al, 2010; Roustan et al, 2014). Atrazine and its metabolites are the most commonly detected pesticide contaminants in groundwater and surface water due to their mobility in soil (Yang et al, 2014). Atrazine has been classified as a priority pollutant since many researches proved it could affect the endocrine system of various kinds of organisms (Lasserre et al, 2009). There were some other reports reveal that atrazine could cause obvious toxic affection on the microorganisms in soil (Muñoz-Leoz et al, 2011; Imfeld and Vuilleumier, 2012). The toxicity of atrazine has raised serious concerns and innovative strategies for remediating atrazine-contaminated soils are critically needed (Lima et al, 2009; Pandey et al, 2009)
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