PhD Oral Defence: Biochar impacts on soil microbiota and potential application of biochar as an inoculant carrier for bioremediation of petroleum hydrocarbon contaminated soil
PhD Oral Defence of Franziska Srocke, Plant Science
This Ph.D. project investigated the use of wood-derived biochars as carriers for bacterial inoculants for bioaugmentation of petroleum hydrocarbon-contaminated soil. Biochar is a carbonaceous solid produced by pyrolysis of biomass and has a highly porous structure suitable for microbial attachment. Using synchrotron X-ray microtomography and multifractal analysis, we demonstrated that the internal structure of softwood pellet biochars consisted of a highly connected, homogenous and isotropic network of pores. Furthermore, the diversity, structure and dynamics of a biochar-immobilized community of hydrocarbon-degrading bacteria was assessed using 16S rRNA gene sequencing. The results showed that biochar properties can cause a significant shift in biochar-associated communities. Biochar particle size also affected community structures (alpha and beta diversity) over time. A soil microcosm experiment revealed that neither biochar amendment nor inoculation with a hydrocarbon-degrading Rhodococcus sp. enhanced the dissipation of petroleum hydrocarbons compared to the control soil after 70 days. However, biochar significantly increased alpha diversity in soil communities, and some biochars caused significant shifts in community composition. Bacterial assemblages on the biochar particles were enriched in Xanthomonadaceae, Flavobacteriaceae and Sphingobacteriaceae, and had higher proportions of Rhodococcus, suggesting that the inoculant persisted on biochar surfaces. This work contributed novel insights into biochar effects on soil microbial communities in contaminated soil. Although these effects did not lead to an improved hydrocarbon degradation, the findings provided evidence that biochars may be used for the purpose of stimulating specific microbial taxa.