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

Abstract

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 CH _4 emissions and has a strong climate forcing feedback; however, the legacy effects of warming winter on CH _4 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 CH _4 emissions in the subsequent growing season. First, in the 3 year field experiment, we continuously measured CH _4 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 NH _4 ^+ –N and more dissolved organic carbon (DOC) in the soil during winter, resulting in high CH _4 emissions. Second, we incubated the paddy soils without flooding at three temperatures (5 °C, 15 °C, and 25 °C) for 4 weeks to simulate warming winter, and subsequently incubated at same temperature (25 °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 NH _4 ^+ –N content in ‘winter season’. The CH _4 emissions in the subsequent ‘growing season’ increased by 190% and 468% when previous incubation temperature increased 10 °C and 20 °C. We showed strong and clear links between warming winter and CH _4 emissions in the subsequent growing season for the first time, suggesting that CH _4 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 CH _4 .

Keywords

• warming winter
• temperature
• methane
• rice paddy
• growing season