Microbial assembly regulated microbial succession of biochar-mediated CH4 biofiltration to resume function under H2S stress

The community assembly processes and the driving factors behind the succession of microbial composition and methanotrophic activities in landfill soil cover under prolonged hydrogen sulfide (H₂S) stress remain poorly understood. Additionally, the role of biochar in mediating coupled methane (CH₄) oxidation and H₂S removal within biofiltration systems warrants further investigation. To address these gaps, three stimulated landfill soil covers with biochar amendment were constructed (50 cm depth) and fed with 50 % CH₄, 50 % CH₄ + 500 ppm H₂S, and 500 ppm H₂S, respectively. Over 253 days, changes in gas removal efficiencies, soil properties, microbial community composition, and functional genes were tracked. The differentiation among treatments was primarily observed in the topsoil. Fresh biochar effectively alleviated the inhibition of methanotrophic activities by adsorbing H₂S, thereby maintaining high CH₄ removal efficiencies initially. However, as biochar reached adsorption saturation and microbial H₂S metabolism intensified, CH₄ removal efficiency was significantly reduced. Over time, the microbial composition and metabolism of the biofiltration system shifted from dominance by Methylocystis (type II) to dominance by Methylocaldum (type I), driven by H₂S selection and microbial interplay-governed deterministic processes. In the final stages, increases in pH and total organic carbon, facilitated by biochar, enhanced the role of stochastic processes, which sustained the equilibrium of the altered methanotroph composition. These changes ultimately restored CH₄ removal efficiencies to above 70 %. This study demonstrates the natural resilience of CH₄ biofiltration systems with biochar as a stimulant and provides new insights into the microbial assembly processes driving successional changes in biofiltration performance.