Biochar-based rhizosphere engineering for enhanced CH 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 (CH) 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 CH removal efficiency across three operational phases: Phase I (continuous CH input), Phase II (fluctuating CH input), and Phase III (resumed continuous CH 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 CH removal efficiency compared to maize straw-derived biochar (SBC). However, MBC-amended soils exhibited diminished resistance to CH 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 CH input fluctuations in Phase II, underscoring the vulnerability of plant-driven systems to variable CH supply. However, biochar emerged as a critical factor in restoring methanotrophic activity upon reintroducing continuous CH 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 CH 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 CH mitigation in landfill environments.