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

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.