Net Ecosystem Exchange of Carbon Dioxide in Rice Summer – Autumn crop of the lower Mekong delta, Vietnam

This study describes the net ecosystem exchange of CO2 in a rice summer-autumn growth season in the lower Mekong Delta, Vietnam. Eddy Covariance and bio-meteorological systems were used to continually record the net CO2 exchange between the paddy field and the atmosphere, together with environmental variables affecting the exchange rate. Rice plant growth (height, above-, and belowground biomass) was measured every 15 days during the entire crop. Our study paddy field emitted CO2 at the mean rate of 5.06 ± 2.49 µmol m-2 s-1, while the rate of CO2 capturing was 18.65 ± 11.76 µmol m-2 s-1 throughout the entire crop. The paddy field acted as a CO2 sink almost during the crop. The quick increase of leaf area from the 15th to the 60th day led to the rise in CO2 influx. The decrease in influx rate after the 60th day resulted from the senescence and death of the aboveground biomass. The drainage in the last ten days of the crop probably contributed to the increase in CO2 effluxes and hence, turned the paddy field into a CO2 source. Ambient temperature was an important factor affecting the rate of CO2 exchange affects the photosynthesis, plant respiration, photorespiration, and organic matter decomposition.