Dissolved organic carbon cycling, methane emissions and related microbial populations in temperate rice paddies with contrasting straw and water management

Rice cultivation is recognised as a pivotal source of atmospheric methane (CH4), accounting for 11% of global emissions. The main drivers of CH4 production are redox conditions of soil, substrate availability, and abundance of methanogenic archaea, all potentially governed by management practices for straw and water management. In the present study, we combined crop residue and water management practices aimed at limiting substrate availability and reducing soil conditions required for methanogenesis, and tested their efficiency for mitigating CH4 emission in a field trial conducted on a long-term experimental platform. Combined straw and water management practices (i.e. the early crop residue incorporation, AUT, the adoption of dry with respect to water seeding, DRY, and the straw removal, REM) were effective in reducing dissolved organic carbon (DOC) concentrations, methanogenic abundances and overall CH4 fluxes, with respect to the typical technique adopted in the Italian rice district that involves spring incorporation of straw and water seeding (SPR). The latter treatment enhanced substrate availability as well as favoured methanogenic archaea abundances and resulted in the highest CH4 fluxes and cumulative emissions. Treatments AUT and REM showed similar behaviours, reducing emissions of SPR by 48% and 46%, respectively. The highest mitigation efficiency was obtained by DRY that reduced emissions by 69% as a result of the oxic soil conditions during the early vegetative stage, the decreased substrate availability with the onset of field flooding, and the lower abundance of methanogenic communities.