###### Abstract  
Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG) after carbon dioxide (CO2), and paddy fields are among the largest sources of CH4 emissions. Owing to the scarcity of observational data, the characteristics and influencing factors of CH4 fluxes in paddy fields at different timescales need to be further investigated. Observations of CH4 fluxes via eddy covariance (EC) data were performed over four seasons in two paddy fields in Nanchang, Jiangqi Province, China. The pattern, magnitude and biophysical controls of CH4 emissions were explored by wavelet analysis and stepwise multiplicative modelling. The results revealed a distinct, single-peak diurnal pattern in CH4 fluxes during the vegetative stage in all four rice growing seasons and the reproductive stage of early rice. Large seasonal variations in daily CH4 emissions were observed in the two double-cropping paddy fields, and the soil temperature at a depth of 5 cm (T5S) explained most of the seasonality of the CH4 fluxes. At the inter-seasonal scale, under local farms' traditional field management method, reducing the amount and frequency of irrigation during the vegetative stage could decrease CH4 emissions in southern China. This study improves the understanding of CH4 emissions and helps in developing GHG management strategies for paddy fields. m 13 June 2021 13 2021 13 2021 1  
Subject: 8 August 2021  
MDPI stays neutral  
We  
CO\({}_{2}\), water vapour and ancillary physical variables (e.g., temperature (T) and soil water content (SWC)) at half-hour intervals provide appropriate conditions for research on the dominant controlling factors of CH\({}_{4}\) fluxes across multiple timescales. The EC technique has been widely used for measuring H\({}_{2}\)O [13; 14; 15; 16], CO\({}_{2}\)[17; 18] and energy [19; 20; 21] fluxes. The effectiveness of EC for measuring CH\({}_{4}\) emission fluxes in different ecosystems [22; 23; 24; 25; 26; 27; 28] has also been confirmed. The emission of CH\({}_{4}\) from paddy fields results from the simultaneous processes of production, oxidation and transportation and highly depends on environmental and biophysical factors. Globally, meteorological factors, such as precipitation, temperature, ambient pressure, soil type and friction velocity (U*) have been reported to affect CH\({}_{4}\) emissions in marshes [12], fans [29], wetlands [23] and paddy fields [30; 31]. Compared with those in other ecosystems, the process of CH\({}_{4}\) emissions in paddy fields is more complex due to the involvement of rice plants and field management. Plant-mediated transport is the primary transport mechanism of CH\({}_{4}\) from the soil to the atmosphere, and diffusion is the dominant mechanism of gas exchange in the paddy fields [32; 33; 34]. Additionally, photosynthesis products are the primary source of carbon substrates for methanogenic metabolism [35; 36]; thus, the plant status can also regulate CH\({}_{4}\) emissions. Moreover, the variation in CH\({}_{4}\) flux is also regulated by field water management [27] and fertilizer applications [37; 38; 39; 40]. These factors act in different processes and interact strongly with each other; thus, the main controlling factors of CH\({}_{4}\) fluxes vary over diverse timescales. For example, carbon assimilation was demonstrated to regulate diurnal CH\({}_{4}\) production with a time lag of 1-1.5 h in rice [32]; the temperature was reported to explain most of the seasonality in CH\({}_{4}\) fluxes [41]; the response of CH\({}_{4}\) emissions to water table fluctuation can be nonlinear, and water table fluctuation lagged the CH\({}_{4}\) flux by up to 10 days [42]. Therefore, exploring the main controlling factors in paddy fields at multiple timescales is necessary.