Novel Biochar-Plant Tandem Approach for Remediating Hexachlorobenzene Contaminated Soils: Proof-of-Concept and New Insight into the Rhizosphere

Abstract

Volatilization of semi/volatile persistent organic pollutants (POPs) from soils is a major source of global POPs emission. This proof-of-concept study investigated a novel biochar-plant tandem approach to effectively immobilize and then degrade POPs in soils using hexachlorobenzene (HCB) as a model POP and ryegrass (Lolium perenne L.) as a model plant growing in soils amended with wheat straw biochar. HCB dissipation was significantly enhanced in the rhizosphere and near rhizosphere soils, with the greatest dissipation in the 2 mm near rhizosphere. This enhanced HCB dissipation likely resulted from (i) increased bioavailability of immobilized HCB and (ii) enhanced microbial activities, both of which were induced by ryegrass root exudates. As a major component of ryegrass root exudates, oxalic acid suppressed HCB sorption to biochar and stimulated HCB desorption from biochar and biochar-amended soils, thus increasing the bioavailability of HCB. High-throughput sequencing results revealed that the 2 mm near rhizosphere soil showed the lowest bacterial diversity due to the increased abundance of some genera (e.g., Azohydromonas, Pseudomonas, Fluviicola, and Sporocytophaga). These bacteria were likely responsible for the enhanced degradation of HCB as their abundance was exponentially correlated with HCB dissipation. The results from this study suggest that the biochar-plant tandem approach could be an effective strategy for remediating soils contaminated with semi/volatile organic contaminants.

Sludge Biochar Amendment and Alfalfa Revegetation Improve Soil Physicochemical Properties and Increase Diversity of Soil Microbes in Soils from a Rare Earth Element Mining Wasteland

“…Devosia, Edaphobacter, Leifsonia, Massilia, Mucilaginibacter, Sinomonas, Sphingomonas and Stenotrophomonas in soil ( p < 0.05), whereas significantly reduced abundances of Exiguobacterium , Citrobacter , Pseudomonas, and Bradyhizobium ( p < 0.05). Arthrobacter, an gram-negative bacterium, was demonstrated to have the ability to degrade hydrocarbons and its’ higher relative abundance was detected in biochar [ 82 , 83 ] and alfalfa-amended soil [ 84 ]. Sphingobium was reported to increase in soil treated with biochar, and can degrade recalcitrant compounds [ 85 ].…”

Differentiation between physical and chemical effects of oil presence in freshly spiked soil during rhizoremediation trial

“…Within the scope of phytoremediation, rhizoremediation is gaining enormous attention (Gerhardt et al 2017 ) and has been accepted as a green or sustainable solution for the remediation of organic contaminants (Song et al 2016 ; Dubey and Fulekar 2013 ) especially petroleum and its derived products (Hou et al 2015 ). Studies on different influencing factors are important for a better understanding of plant growth in TPH-impacted soils during rhizoremediation.…”

Straw biochar strengthens the life strategies and network of rhizosphere fungi in manure fertilized soils

“…Graber et al (2010) demonstrated that some compounds in biochar, like volatile organic compounds, are microbial inhibitors that can induce toxicity directly to soil microbial pathogens, thereby benefitting plant growth. In addition to the above mechanisms, ryegrass roots indirectly affect successional rates of fungal communities via root secretion of compounds (Song et al, 2016). The dependence of all the above temporal changes on particular environmental stresses or rather, whether they change randomly with succession, requires further investigation.…”

“…Variation of microbial diversity in soil may be regulated through the supply of organic matter nutrients (Cookson et al, 2005;Housman et al, 2007). The secretions of plant roots can also affect microbial communities through the provision of available carbon sources (Song et al, 2016).…”