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

Abstract

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 15^th to the 60^th day led to the rise in CO₂ influx. The decrease in influx rate after the 60^th 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.