Plant-microbiome assisted and biochar-amended remediation of heavy metals and polyaromatic compounds - a microcosmic study

The study has been carried out to develop a plant-microbes assisted remediation technology to accelerate polyaromatic hydrocarbons (PAHs) degradation and heavy metals (HMs) removal in a microcosmic experiment. The quaternary mixture of PAHs (phenanthrene, anthracene, pyrene, and benzo [a] pyrene) and metals (Cr, Ni, and Pb) spiked the soil, constructing a microcosm; the microcosms were bioaugmented with newly developed plant bacterial consortia (Cpm(1) and Cpm(2)). The microcosms were amended with biochar (sieved particle size 0.5-2 mm) as redox regulators to reduce oxidative stress of plant-microbe systems. To formulate the two plant-bacterial consortia, plant species were collected and bacteria were isolated from oil spill soil. The bacterial strains used in two formulated consortia includes - Cpm(1) (Enterobacter cloacae HS32, Brevibacillus reuszeri HS37, and Stenotrophomonas sp. HS16) and Cpm(2) (Acinetobacter junii HS29, Enterobacter aerogenes HS39 and Enterobacter asburiae HS22). The PAHs degradation and metal removal efficacy of the consortia (Cpm(1) and Cpm(2)) were studied after 24 weeks of trial. The physicochemical properties of microcosm's soil (M-2 and M-3) were assessed after experimentation, which resulted in the finding that the soil exhibits dropped in pH from basic to neutral after application of the plant microbes consortium. The electrical conductivity was lower in M-2 and M-3 soils, with a range between 1.60 and 1.80 mS/cm after the treatment. The Gas Chromatography/Mass Spectrometry (GC/MS) results illustrate how metabolites with the different molecular weight (M.W) were found in M-2 and M-3 soils (184-446), as a result of the plant-microbes mediated rhizodegradation of four spiked PAHs. The metals in microcosm's soil are very low in concentration after 24 weeks of trial when compared to control (M-1). The Cr, Ni and Pb removal percentages were found in 45.79, 42.19 and 44.85 in M-2. However, the removal percentages were found to be 45.41, 41.47 and 44.25 respectively for these same HMs in M-3 soil. Both the consortia that were newly developed showed similar trends of metals removal and PAHs degradation. This study provides a breakthrough in the area of rhizosphere engineering with the goal of maintaining a sustainable application of plant-microbes in ecosystem services.