Gross Ecosystem Productivity Dominates the Control of Ecosystem Methane Flux in Rice Paddies.

Although rice paddy fields are one of the world's largest anthropogenic sources of methane CH₄, the budget of ecosystem CH₄ and its' controls in rice paddies remain unclear. Here, we analyze seasonal dynamics of direct ecosystem-scale measurements of CH₄ flux in a rice-wheat rotation agroecosystem over 3 consecutive years. Results showed that the averaged CO₂ uptakes and CH₄ emissions in rice seasons were 2.2 and 20.9 folds of the wheat seasons, respectively. In sum, the wheat-rice rotation agroecosystem acted as a large net C sink (averaged 460.79 g C m^-2) and a GHG (averaged 174.38 g CO₂eq m^-2) source except for a GHG sink in one year (2016) with a very high rice seeding density. While the linear correlation between daily CH₄ fluxes and gross ecosystem productivity (GEP) was not significant for the whole rice season, daily CH₄ fluxes were significantly correlated to daily GEP both before (R²: 0.52-0.83) and after the mid-season drainage (R²: 0.71-0.79). Furthermore, the F partial test showed that GEP was much greater than that of any other variable including soil temperature for the rice season in each year. Meanwhile, the parameters of the best-fit functions between daily CH₄ fluxes and GEP shifted between rice growth stages. This study highlights that GEP is a good predictor of daily CH₄ fluxes in rice paddies. [ABSTRACT FROM AUTHOR]