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

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.

The Linkage Between Methane Fluxes and Gross Primary Productivity at Diurnal and Seasonal Scales on a Rice Paddy Field in Eastern China

“…We also found a significant relationship between daily GPP and CH 4 fluxes during the growing seasons of 6 years (Figure 5), which was in agreement with previous findings (Dai et al., 2019; Knox et al., 2016; Li et al., 2021; Ström et al., 2012). The reason was that a large amount of labile organic carbon was allocated to the rhizosphere through the exudation of root tissues and plant turnover to stimulate CH 4 production (Lai et al., 2014).…”

“…Mean daily CH 4 /GPP in growing seasons ranged from 3.5% to 6.4% at this rice paddy field (Table 1), consistent with the results of Ge et al (2018) and L. Ma et al (2021). However, it was significantly higher than the values (<3%) reported by other studies (Bao et al, 2022;Bhattacharyya et al, 2014;Li et al, 2021;Meijide et al, 2017;Miyata et al, 2005;Shim et al, 2016), which can be attributed to the differences in water management and crop fertilizer application. Based on the global meta-analysis, L. Zhou et al (2021) found that the seasonal ratio of CH 4 to NEE was 0.269% in the rice paddy.…”

“…(2021). However, it was significantly higher than the values (<3%) reported by other studies (Bao et al., 2022; Bhattacharyya et al., 2014; Li et al., 2021; Meijide et al., 2017; Miyata et al., 2005; Shim et al., 2016), which can be attributed to the differences in water management and crop fertilizer application. Based on the global meta‐analysis, L. Zhou et al.…”