Reduced nitrogen fertilizer application mitigated CH₄ fluxes from rice paddies under an elevated CO₂ concentration

Nitrogen (N) fertilizer is a critical factor in achieving high rice yields, but it can also contribute to increased CH₄ emissions from rice paddies. Determining how to utilize N fertilizer to effectively balance the contradiction between methane (CH₄) emissions and rice yield remains an urgent need in the face of unstoppable climate change.

In this study, the response of CH₄ fluxes in rice paddies to elevated carbon dioxide (CO₂) concentration (e[CO₂]) and reduced N application were investigated. The rice biomass and yield, CH₄ fluxes, soil properties, and methanogenic characteristics were observed in control (CK) (ambient CO₂ concentration + application of 250 kg N ha⁻¹ urea), C⁺ (e[CO₂] by 200 ppm + 250 kg N ha⁻¹ urea), N⁻ (ambient CO₂ concentration + 150 kg N ha⁻¹ urea), and C⁺N⁻ (e[CO₂] by 200 ppm + 150 kg N ha⁻¹ urea) treatments.

The results revealed that the C⁺ and C⁺N⁻ treatments significantly increased the CH₄ emissions/yield by 20.0% and 18.8%, respectively, while the N⁻ treatment significantly suppressed the CH₄ emissions/yield by 13.3% compared to CK. The N⁻ treatment weakened the promotion effect of C⁺ on the rice total biomass, the soil dissolved organic carbon (DOC) concentration and invertase activity, and the CH₄ emissions/yield. Moreover, the C⁺N⁻ treatment significantly reduced the soil DOC concentration and the abundance of the mcrA gene in the grain-filling stage compared to C⁺.

Overall, under climate change conditions, N reduction can mitigate CH₄ fluxes from rice paddies by affecting rice growth, soil methanogenic characteristics, and the C substrate.