[Response of Yield, CH₄, and N₂O Emissions from Paddy Fields to Long-term Elevated CO₂ Concentrations]

Elevated atmospheric CO₂ concentrations([CO₂]_e) are the main driving force of global climate change, which directly and indirectly affect carbon and nitrogen cycling in the paddy ecosystems. Therefore, understanding the response of rice yield and greenhouse gas emissions to long-term(more than 10 years)[CO₂]_e from paddy fields is of great significance for food security and future climate change assessment. In this study, strongly and weakly responsive cultivars were used as the experimental materials. Based on a free-air CO₂ enrichment(FACE) platform continuously run for 14 years, two treatments of different[CO₂] were set:a control(i.e., normal[CO₂] and[CO₂]_a) and a 200 μmol·mol^-1 higher than[CO₂]_a condition, ([CO₂]_e). CH₄ and N₂O emissions from the rice paddy fields were monitored in situ by static transparent chamber-gas chromatography, and grain yields were also obtained. The results showed that compared with the[CO₂]_a treatment, long-term[CO₂]_e increased grain yields of the strongly and weakly responsive cultivars by 29%-31%(P<0.05) and 12%-14%(P>0.05), and CH₄ emissions of the strongly and weakly responsive cultivars were reduced by 21%-59% and 11%-54%, respectively. Furthermore, N₂O emissions from the strongly and weakly responsive cultivars were significantly reduced by 70%(P<0.05) and 40%(P<0.05), respectively. The short- and long-term responses of grain yields and CH₄ emissions from rice paddy fields to[CO₂]_e were significantly different. Specifically, with the increase in the duration of[CO₂]_e, the increases in rice yields and CH₄ emissions significantly decreased, while the N₂O emissions showed no significant changes. Therefore, under long-term[CO₂]_e conditions, the strongly responsive cultivar has a high potential to reduce greenhouse gas emission and increase grain yields.