Estimation of respiratory parameters for rice based on long-term and intermittent measurement of canopy CO2 exchange rates in the field.

Estimation of respiratory parameters, such as maintenance coefficient and growth conversion efficiency, is important for simulating crop growth. The objective of this study was to estimate respiratory parameters for rice (Oryza sativa L.) by model analysis based on long-term and intermittent measurement of canopy CO2 exchange rate (CER) in the field conditions. Canopy CER was intermittently measured in the field conditions for three rice varieties every 30 min from around the panicle initiation stage to maturity in 2004. Based on this measurement, rice respiration model was established and respiratory parameters were estimated by Simplex method. There was a big difference in respiration rate among rice varieties and large seasonal changes as evidenced by the long-term and intermittent measurement of canopy CER. The model explained the varietal difference and seasonal changes in respiration rate without any bias despite that all respiratory parameters, maintenance coefficient and growth conversion efficiency, were fixed for the three varieties. The results indicated that genotypic differences and seasonal changes in respiration rate result not from differences in respiratory parameters, but from differences in dry matter production, its allocation, and the N concentration of each tissue. Estimated respiratory parameters explained well the large variations in the directly measured canopy respiration rate of field grown rice. The model analysis suggested that the varietal differences and seasonal changes in canopy respiration rate were caused by differences in the dynamics of dry matter and nitrogen accumulation in plants. (c) 2008 Elsevier B.V. All rights reserved.