Biochar-based rhizosphere engineering for enhanced CH₄ removal in landfill cover soil

Rhizosphere engineering represents a promising strategy for augmenting methanotrophic activity in landfill cover soil (LCS). However, the mechanistic interplay between plant-biochar combinations and their collective influence on the rhizosphere-mediated regulation of methane (CH₄) biofiltration processes remains inadequately elucidated. This study systematically investigated the efficacy of vegetated LCS systems by integrating three herbaceous plant species with two distinct biochar types, evaluating CH₄ removal efficiency across three operational phases: Phase I (continuous CH₄ input), Phase II (fluctuating CH₄ input), and Phase III (resumed continuous CH₄ input). During Phase I, vegetation played a pivotal role in shaping rhizosphere microbial communities, with Solanum americanum-planted LCS demonstrating superior methanotrophic activity, attributable to its favorable metabolite profile. Swine manure-derived biochar (MBC) significantly enhanced CH₄ removal efficiency compared to maize straw-derived biochar (SBC). However, MBC-amended soils exhibited diminished resistance to CH₄ starvation during Phase II, a phenomenon correlated with reduced availability of root-derived metabolites. Instead, rhizosphere microbial communities with enhanced nutrient-importing capacities demonstrated greater retention of methanotrophic activity. The dominance of rhizosphere-mediated effects was disrupted by CH₄ input fluctuations in Phase II, underscoring the vulnerability of plant-driven systems to variable CH₄ supply. However, biochar emerged as a critical factor in restoring methanotrophic activity upon reintroducing continuous CH₄ input in Phase III. Notably, MBC proved more effective than SBC in elevating soil organic carbon content while concurrently reducing ammonia nitrogen concentrations in the rhizosphere, thereby fostering a more robust recovery of CH₄ removal capacity. This study underscores the synergistic potential of plant-biochar co-application in enhancing the resistance and resilience of soil microbial communities and methanotrophic activities within engineered ecosystems. These findings provide critical insights into optimizing rhizosphere engineering strategies for sustainable CH₄ mitigation in landfill environments.