Net ecosystem CO2 exchange and carbon cycling in tropical lowland flooded rice ecosystem

The seasonal fluxes of CO 2 and its characteristics with relation to environmental variables were investigated under tropical lowland flooded rice paddies employing the open path eddy covariance technique. The seasonal net ecosystem carbon budget was quantified by empirical modelling approach. The integrated net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (RE) in the flooded rice field was −448, 811 and 363 g C m −2 in wet season. Diurnal variations of mean NEE values during the season varied from +3.99 to −18.50 μmol CO 2 m −2 s −1 . The daily average NEE over the cropping season varied from +2.73 to −7.74 g C m −2 day −1 . The net ecosystem CO 2 exchange reached its maximum in heading to flowering stage of rice with an average value of −5.67 g C m −2 day −1 . On daily basis the flooded rice field acted as a net sink for CO 2 during most of the times in growing season except few days at maturity when it became a net CO 2 source. The rate of CO 2 uptake by rice as observed from negative NEE values increased proportionally with air temperature up to 34 °C. The carbon distribution in different component of soil-plant system namely, soil organic carbon, dissolved organic carbon, methane emission, rhizodeposition, carbon in algal biomass, crop harvest and residues were quantified and carbon balance sheet was prepared for the wet season in tropical rice. Carbon balance sheet for tropical rice revealed 7.12 Mg C ha −1 was cycled in the system in wet season.