Diel and seasonal variation in CO2 flux of irrigated rice

Rice is a primary food source for half the world's population, but little is known of how temporal changes in the field-scale physical environment affect carbon dioxide exchange rate (CER), biomass accumulation, and crop yield. Experiments were conducted in 1998 and 1999 in a commercial field near El Campo, TX, to evaluate interactions between CER and the physical environment. Tower-based conditional sampling was used to measure CER. Environmental parameters such as photosynthetically active radiation (PAR), net radiation, and temperature were measured along with CER. Whole-plant biomass was also collected throughout both seasons. Fluctuations in diel CER were correlated with changes in PAR, while season-long trends in CER were associated with changes in leaf area index and stage of development. Crop yield was found to be directly related to total carbon-dioxide exchange after heading, and may have been affected by environmental conditions at anthesis, such as temperature and wind speed, or leaf nitrogen status, both of which differed considerably between the two seasons. Data showed a positive correlation between biomass accumulation and cumulative CER for both years of the study. (C) 2001 Elsevier Science B.V. All rights reserved.