Temporal variations of δ¹³C-CH₄ in rice paddies dominated by the plant-mediated pathway

The stable carbon isotope signature of methane (δ¹³C-CH₄) helps constrain CH₄ emissions on regional to global scales, yet observations in rice paddies remain limited. The temporal dynamics of δ¹³C-CH₄ and its drivers in rice paddies are still not fully understood. Here, we conducted continuous in situ observations of CH₄ and δ¹³C-CH₄ at three canopy heights throughout a rice growing season. We investigated the emission source signature (δ¹³C_source) and partitioned it into plant-mediated (δ¹³C_P) and non-plant-mediated (δ¹³C_NP) pathways. δ¹³C_source exhibited significant temporal and vertical variability, influenced by transport pathways and external sources. We found that temporal variations in δ¹³C_source were strongly correlated with rice photosynthesis and predominantly driven by δ¹³C_P. Our results show that plant-mediated transport, rather than CH₄ production, dominates δ¹³C_source variability. These findings provide new insight into the δ¹³C_source dynamics in rice paddies and will be crucial for improving regional-to-global estimates of CH₄ fluxes from rice agriculture.