Methane emissions from typical paddy fields in Liaohe Plain and Sanjiang Plain, Northeast China

Methane is one of the most important greenhouse gases and is emitted from waterlogged rice regions. Eddy covariance was used to obtain long-term (2017-2018), high-frequency data for the CH(4)flux at typical rice paddy fields in Sanjiang Plain and Liaohe Plain. This study examines the CH(4)emission process, emission characteristics at different time scales and the intensity of different emission sources. The relationships between CH(4)emissions and temperature and photosynthetically active radiation were also analysed. CH(4)emissions from Sanjiang Plain and Liaohe Plain in 2017 were 26.77 and 16.17 g CH(4)m(-2)year(-1), respectively. The CH(4)fluxes in 2017 and 2018 were similar; emissions were higher at the Sanjiang site in 2018. Peak CH(4)emissions (daily average: 0.127 mu mol CH(4)m(-2)s(-1)) corresponded to the tillering stage in Sanjiang Plain. CH(4)emissions peaks corresponding to the jointing-heading and mature stages at Liaohe Plain. Monthly CH(4)emissions were highest in July. The daily averaged flux was 0.065 mu mol CH(4)m(-2)s(-1)during the growing season. The field-transplanting stage exhibited the highest CH(4)emissions. No CH(4)was emitted during the greening-tillering stages. Emissions increased again during the jointing-heading stages to 0.102 mu mol CH(4)m(-2)s(-1), and then decreased gradually. A significant linear correlation was observed between PAR and the methane flux in Liaohe Plain. CH(4)emissions in Sanjiang Plain were more sensitive to changes in temperature. The temperature coefficient value was highest from the sowing period to the green period. The CH(4)flux at Sanjiang Plain depended on the stage of rice growth, the temperature, the degree of irrigation and drainage, and the soil pH. In November (during the non-growing season) at Liaohe Plain, a slight negative flux (a weak CH(4)sink) was observed. CH(4)emissions were also found to be inhibited in the growing season by increased soil alkalinity.