Ethylene stimulates methane oxidation and inhibits methane production in green manure-rice systems

Green manure is effective for improving rice yields and soil quality, but it might result in increasing methane (CH₄) emissions in paddy fields caused by its substantial organic matter. Finding approaches to mitigate CH₄ emissions while guaranteeing grain yields are urgently needed. The impacts and underlying mechanisms of applying ethylene on CH₄ emissions in milk vetch (MV)-rice pattern were explored. Field and pot experiments were carried out simultaneously for a 2 year with three treatments: no MV-rice (CK), MV-rice (GM), and MV-rice by applying ethylene when incorporating MV (GM + ETH). Planting MV (GM) effectively improved rice productivity but increased CH₄ emissions relative to CK. Compared with GM, GM + ETH significantly reduced cumulative CH₄ emissions by 39.6 %-52.9 % in a field experiment and by 44.4 % in a pot experiment. In the pot experiment indicated that applying ethylene had the highest aerenchyma ratio, which was 1.65 and 3.81 times higher than CK and GM treatments. Ethylene application improved soil CH₄ oxidation potential by 7.5 % and diminished CH₄ production potentials by 34.0 % relative to GM. The improvement of root aerenchyma facilitated oxygen release by 8.4 %-23.4 %, increased root oxidation activity by 16.4 %, and decreased the contents of soil reducing substances (including total reducing substance, active reducing substance, and Fe²⁺), leading to the increase of pmoA abundances by 39.7 % and the reduction mcrA abundances by 32.3 % when compared with GM, respectively. These findings provided solutions for improving the productivity by using green manure as well as controlling the CH₄ emissions in paddy fields.