Abstract
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.
Highlights
Rice paddies provide the dominant staple food crop for over 5 billion people worldwide while acting as a major source of atmospheric methane (CH4) which is the second most important greenhouse gas following carbon dioxide (CO2) [1,2]
CH4 fluxes sharply increased when the field was first flooded for the rice season in June
We analyzed 3 consecutive years of eddy covariance measurements of CH4 fluxes from a rice-wheat rotation agroecosystem located in Southeast China
Summary
Rice paddies provide the dominant staple food crop for over 5 billion people worldwide while acting as a major source of atmospheric methane (CH4) which is the second most important greenhouse gas following carbon dioxide (CO2) [1,2]. Previous studies on global estimation of CH4 emissions from rice paddies showed that the budget of CH4 flux remain great uncertainties [2,3], which indicated more efforts are needed to understand the responses of CH4 flux to biological and environmental factors. Previous CH4 flux from rice paddies have predominantly been measured using the manual closed chamber technique [4,5]. The eddy covariance (EC) technique advantaged in measuring CH4 flux since it provides continuous ecosystem-scale CH4 flux without interfering with the processes of gas exchange between the surface and the atmosphere [6,8]. Several studies using EC methods have advantaged our understanding of the dynamics and process of CH4 flux from rice paddies [9,10,11]. To date few studies have used this method to measure CH4 flux from rice paddies in China [9,10]
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