Characterization of carbon dioxide fluxes in tropical lowland flooded rice ecology

Characterization of carbon dioxide (CO2) fluxes was investigated in tropical lowland flooded rice ecology using open path eddy covariance (EC) technique during dry season of 2009–2010. Select environmental variables like air and soil temperatures, soil moisture, net radiation, photosynthetically active radiation, vapour pressure deficit and soil heat flux were monitored throughout the season and correlated with half hourly CO2 fluxes. The study was conducted to gain insight of environmental impact in terms of carbon (C) budget in a submerged soil of tropical region planted to rice. Total C budget integrated over dry season expressed in terms of net ecosystem CO2 exchange (NEE) was − 392 g C m−2, while the gross primary production (GPP) and ecosystem respiration (RE) were 731 and 339 g C m−2, respectively. Seasonal daily mean NEE, GPP and RE were − 3.73, 6.96 and 3.23 g C m−2 d−1, respectively. The ratio of RE/GPP in flooded rice field was 0.46. The NEE was negative during daytime and positive during nighttime, i.e. rice paddy ecosystem acted as a CO2 sink and source during daytime and night hours, respectively. Lowest negative NEE was found during heading to flowering stage (− 26.93 µmol CO2 m−2 s−1) of crop growth due to estimated highest values of GPP (32.34 µmol CO2 m−2 s−1) and RE (5.42 µmol CO2 m−2 s−1). On seasonal basis flooded rice ecology behaved as net sink for CO2. This was attributed to higher photosynthetic capacity of lowland rice to convert atmospheric C into organic compounds and slow organic matter decomposition in flooded soils.