Chloropicrin fumigation disrupts the balance between methanotrophs and methanogens in soil and stimulates methane...

Soil fumigation suppresses soil-borne pathogens but also non-target microorganisms, potentially altering soil carbon cycling. However, its impact on soil methane (CH₄) metabolism, remains poorly understood. This study investigates the effects of chloropicrin (CP) fumigation on soil carbon dynamics and the microbial mechanisms underlying CH₄ emissions. The results unveiled that CP fumigation significantly increased soil dissolved organic carbon by 68.7 %-217.5 %, enhanced CH₄ emissions by 9.5 %-165.3 %, and promoted carbon dioxide (CO₂) emissions by 14.0 %-60.6 % from days 35-77. CP fumigation directly promoted CH₄ emissions through changes in mcrA and pmoA gene abundances, carbon environmental factors, and CO₂ concentration. By day 49 post-fumigation, methanotroph abundance and diversity had declined markedly, whereas methanogen abundance increased, indicating greater sensitivity of methanotrophs to CP fumigation. Functionally, CP fumigation severely inhibited CH₄ oxidation to formaldehyde (HCHO) and methanol (CH₃OH) and suppressed the tetrahydromethanopterin (H₄MPT) methanotrophic pathway, while promoting acetate-dependent methanogenesis. Only minor inhibition was observed in the CO₂ reduction pathway. Together, these changes stimulated the CH₄ emissions. This study presents the first evidence that soil fumigation substantially alters soil CH₄ cycling, revealing its broader ecological consequences.