Ratoon Season Rice Reduces Methane Emissions by Limiting Acetic Acid Transport to the Rhizosphere and Inhibiting Methanogens

Rice paddies are a major, persistent source of atmospheric methane (CH₄), emission rates depend on the partitioning of photosynthate carbon between the rice plant and the rhizosphere microbiome. Although ratoon season rice (RR) is shown to emit far less CH₄ than main-crop rice (MC), the mechanisms have remained unresolved. This work conducts a 2-year field experiment in which RR is compared with MC and with late rice (LR) synchronized to the RR heading stage. Relative to MC and LR, RR lowers daily CH₄ flux by 91%, raises daily grain yield by 34%-57%, and increases net economic return by 90%-136%. Mechanistically, ¹³C-labelling reveals that RR diverted more newly fixed carbon to the grain and less to the rhizosphere, thereby restricting acetate availability for methanogens. Rhizosphere metagenomics show reduced abundance of Methanobacteriaceae and down-regulation of methanogenic genes in RR. This carbon-reallocation pattern is underpinned by an abscisic acid (ABA)-mediated interaction between OsCIPK2 and OsSWEET1A, which simultaneously curtailed carbon efflux from roots and enhanced grain filling. This study is the first to establish a comprehensive framework of "ABA regulation-carbon allocation-microbial function-emission reduction and efficiency enhancement." It provides targetable strategies for carbon allocation and microbial management within climate-smart rice farming systems.