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

## TL;DR

This study tracks methane and its carbon isotope in rice paddies to show how plant processes influence methane emissions over time.

## Contribution

The study reveals that plant-mediated transport, not methane production, drives isotope variability in rice paddies.

## Key findings

- δ13Csource varies seasonally and with canopy height.
- Rice photosynthesis strongly influences δ13Csource.
- Plant-mediated transport dominates δ13Csource variability.

## Abstract

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 (δ13Csource) and partitioned it into plant-mediated (δ13CP) and non-plant-mediated (δ13CNP) pathways. δ13Csource exhibited significant temporal and vertical variability, influenced by transport pathways and external sources. We found that temporal variations in δ13Csource were strongly correlated with rice photosynthesis and predominantly driven by δ13CP. Our results show that plant-mediated transport, rather than CH4 production, dominates δ13Csource variability. These findings provide new insight into the δ13Csource dynamics in rice paddies and will be crucial for improving regional-to-global estimates of CH4 fluxes from rice agriculture.

•Continuous in situ observations of CH4 and δ13C-CH4 were conducted in rice paddies•Significant seasonal variations in δ13Csource are revealed•δ13Csource is linked to rice photosynthesis and dominated by plant-mediated transport•GPP is suggested as a potential proxy for CH4 emission at large spatial scales

Continuous in situ observations of CH4 and δ13C-CH4 were conducted in rice paddies

Significant seasonal variations in δ13Csource are revealed

δ13Csource is linked to rice photosynthesis and dominated by plant-mediated transport

GPP is suggested as a potential proxy for CH4 emission at large spatial scales

Isotope geochemistry; Isotope chemistry; Plant Biology; Biogeoscience; Biogeochemistry