The warming winter accelerated methane emissions during subsequent rice growing season from paddy fields

Global temperature is projected to increase, which impacts the ecological process in northern mid- and high-latitude ecosystems, but the winter temperature change in ecosystems is among the least understood. Rice paddy represents a significant contributor to global anthropogenic CH4 emissions and has a strong climate forcing feedback; however, the legacy effects of warming winter on CH4 emissions in the subsequent growing season remain uncertain. Here, we conducted field and incubation experiments to determine the effects of winter soil temperature changes on CH4 emissions in the subsequent growing season. First, in the 3 year field experiment, we continuously measured CH4 emissions from the rice cropping system. The winter soil temperature and its variation showed significant differences over the 3 years. In the warming-winter year, the rice paddy accumulated less NH4 (+)-N and more dissolved organic carbon (DOC) in the soil during winter, resulting in high CH4 emissions. Second, we incubated the paddy soils without flooding at three temperatures (5 degrees C, 15 degrees C, and 25 degrees C) for 4 weeks to simulate warming winter, and subsequently incubated at same temperature (25 degrees C) under submerged conditions for 4 weeks to simulate growing season. The result was consistent with field experiment, increased soil temperature significantly increased soil DOC content and decreased NH4 (+)-N content in 'winter season'. The CH4 emissions in the subsequent 'growing season' increased by 190% and 468% when previous incubation temperature increased 10 degrees C and 20 degrees C. We showed strong and clear links between warming winter and CH4 emissions in the subsequent growing season for the first time, suggesting that CH4 related processes respond not only to warming during the growing season but also in the previous winter. Our findings indicate that nonuniform global warming causes a disproportionate increase in climate forcing feedback to emit more CH4.