Abstract:

To reveal the effects of different water and carbon management on CO₂ exchange between paddy ecosystem and atmosphere, based on field experiments, the diurnal variation characteristics of net CO₂ flux in paddy field ecosystem under different water and carbon management modes were analyzed. The results showed that the change trend of net CO₂ flux in paddy field ecosystem at tillering stage, jointing and booting stage and milky stage was U-shaped, which showed that it was generally absorbed during the day and discharged at night, and the net absorption stage and net emission stage in each growth period were consistent in time. With the advance of growth period, the net CO₂ absorption duration and amount in daytime of paddy field ecosystem presented the trend of increasing at first and then decreasing. In addition to the treatment of high amount of biochar at tillering stage, which reduced the net CO₂ absorption flux in the paddy field ecosystem during the day, the application of biochar increased the net CO₂ absorption flux during the day and the net CO₂ emission flux in the night of the water-saving irrigation paddy field ecosystem. Compared with the treatment without biochar, the net CO₂ flux of paddy field ecosystem during the day and at night were increased by 2.26%-27.16% and 2.30%-32.69% under the two biochar conditions. Water-saving irrigation reduced the net absorption flux of CO₂ in paddy field ecosystem during the day, but increased the net emission flux of CO₂ in paddy field ecosystem at night. The variation ranges of daytime absorption and night emission were 2.68%-59.79% and 1.26%-40.95%. The research results could provide a theoretical basis for realizing the efficient utilization of paddy field water resources and giving full play to the carbon sink function of paddy field ecosystem.

Key words: biochar, water saving irrigation, paddy ecosystem, net CO₂ flux, diurnal variation