Aboveground morphological traits do not predict rice variety effects on CH4 emissions

• Significant differences in CH4 emissions were found among rice varieties.
• CH4 emissions and dissolved CH4 were not correlated to rice aboveground traits.
• The CH4 flux was significantly correlated to the dissolved CH4 in soil solution.
• Aboveground of rice plant might affect CH4 emissions indirectly through the belowground.

High-yield varieties with low methane emissions will benefit sustainable rice (Oryza sativa L.) production. However, no specific plant characteristics have been identified to be primarily responsible for rice variety impacts on the CH4 emission. We conducted a comprehensive study through comparing effects of 66 varieties on CH4 under both greenhouse and field conditions to identify rice plant characteristics that may significantly affect soil CH4 emission. Although there were significant differences in CH4 emissions among the tested rice varieties, no significant and consistent relationships were observed between aboveground traits and CH4 fluxes or dissolved CH4 concentrations in soil solutions. Yet dissolved CH4 concentrations were significantly correlated with the mean CH4 flux over the growing season. In addition, cutting rice plants 5 cm off above the floodwater did not increase CH4 fluxes, indicating that the CH4 transport through the removed part of rice plant contributed little to the total CH4 emission. Taken together, our results indicate that differences in CH4 emissions among rice varieties primarily stem from the differential effects of rice plants on the belowground CH4 production and oxidation. Aboveground plant traits do not provide reliable predictions of variety effects on CH4 emissions. Future efforts should be focused on understanding belowground processes and the underlying mechanisms that govern rice variety impacts on the CH4 emission.