Methane emission in four rice varieties as related to sugars and organic acids of roots and root exudates and biomass yield

Rice (Oryza sativa L.) fields contribute to global methane (CH4) emission and warming. This study determined cultivar variations in CH4 emission in relation to sugar and organic acid composition of the roots and root exudates and shoot and root biomass at the vegetative, reproductive and ripening stages of the rice plant. Thai cultivars Supanburi 1 (SP1), Supanburi 60 (SP60), Supanburi 90 (SP90) and Chainat 1 (CN1) were used. CH4 flux rates were comparably higher in CN1 and SP1 than in SP60 and SP90. Glucose and acetic acid were the predominant sugar and organic acid, respectively. Sugar and organic acid contents of root exudate had no direct relationship with CH4 fluxes regardless of growth stage. Total sugars of root tissues did not similarly compare with CH4 flux rates. However, at the ripening stage, root glucose content was higher in CN1 while root fructose and acetic acid contents were higher in SP1. Shoot and root weights at the different growth stages were also consistently higher in SP1 and CN1 (high-CH4 emitters) than in SP60 and SP90 (low-CH4 emitters). The results demonstrate cultivar-dependent rates of CH4 production due to some compositional differences and provide fundamental basis for cultivar selection as a mitigation strategy to reduce CH4 emission from ricefields.