Increased night temperature reduces the stimulatory effect of elevated carbon dioxide concentration on methane emission from rice paddy soil

<jats:title>Abstract</jats:title><jats:p>To determine how elevated night temperature interacts with carbon dioxide concentration ([CO<jats:sub>2</jats:sub>]) to affect methane (CH<jats:sub>4</jats:sub>) emission from rice paddy soil, we conducted a pot experiment using four controlled‐environment chambers and imposed a combination of two [CO<jats:sub>2</jats:sub>] levels (ambient: 380 ppm; elevated: 680 ppm) and two night temperatures (22 and 32 °C). The day temperature was maintained at 32 °C. Rice (cv. IR72) plants were grown outside until the early‐reproductive growth stage and then transferred to the chambers. After onset of the treatment, day and night CH<jats:sub>4</jats:sub> fluxes were measured every week. The CH<jats:sub>4</jats:sub> fluxes changed significantly with the growth stage, with the largest fluxes occurring around the heading stage in all treatments. The total CH<jats:sub>4</jats:sub> emission during the treatment period was significantly increased by both elevated [CO<jats:sub>2</jats:sub>] (<jats:italic>P</jats:italic>=0.03) and elevated night temperature (<jats:italic>P</jats:italic><0.01). Elevated [CO<jats:sub>2</jats:sub>] increased CH<jats:sub>4</jats:sub> emission by 3.5% and 32.2% under high and low night temperature conditions, respectively. Elevated [CO<jats:sub>2</jats:sub>] increased the net dry weight of rice plants by 12.7% and 38.4% under high and low night temperature conditions, respectively. These results imply that increasing night temperature reduces the stimulatory effect of elevated [CO<jats:sub>2</jats:sub>] on both CH<jats:sub>4</jats:sub> emission and rice growth. The CH<jats:sub>4</jats:sub> emission during the day was larger than at night even under the high‐night‐temperature treatment (i.e. a constant temperature all day). This difference became larger after the heading stage. We observed significant correlations between the night respiration and daily CH<jats:sub>4</jats:sub> flux (<jats:italic>P</jats:italic><0.01). These results suggest that net plant photosynthesis contributes greatly to CH<jats:sub>4</jats:sub> emission and that increasing night temperature reduces the stimulatory effect of elevated [CO<jats:sub>2</jats:sub>] on CH<jats:sub>4</jats:sub> emission from rice paddy soil.</jats:p>