Microbial Abundance and Activity in Biochar-Amended Landfill Cover Soils: Evidence from Large-Scale Column and Field Experiments

Abstract

Field and laboratory studies were conducted to evaluate the impact of biochar amendment on methane oxidation rates and microbial communities in landfill cover soils. Deoxyribonucleic acid (DNA) was isolated from soil and biochar-amended soil following incubation in laboratory soil columns and from samples collected from four test plots installed within the intermediate cover of an active landfill in northeastern Illinois. Next-generation sequencing of 16SrRNA gene amplicons following polymerase chain reaction (PCR) amplification was used to assess the community composition and relative abundance of methane-oxidizing bacteria among the samples. In field soil samples from both soil and biochar-amended soil covers, Type-I methanotrophs (primarily Methylomonas and Crenothrix species) were observed and prevailed over Type-II methanotrophs in terms of relative abundance, comprising 83 to >99% of the total methanotrophic community. Non–methane-oxidizing methylotrophs (e.g., Methylibium, Methyloversatilis, Hyphomicrobium, Bradyrhizobium) and facultative methanotrophs (e.g., Methylocella) were also detected along with obligate methanotrophs, reflecting a diverse bacterial community. Methane oxidation rates in batch assays were positively correlated with relative abundance of methanotrophs as well as methane concentration at depth in the soil at the time of sampling. These trends indicate a significant relationship between methane exposure history and methanotrophic community abundance and composition.