Evaluation of rice drought stress response using carbon isotope discrimination.

Recent studies have used carbon isotope discrimination (△) to investigate crop water use efficiency in drought environments. The main objective of this study was to accurately evaluate the physiological responses to different degrees of drought stress in rice. For two planting patterns: plant pattern1 (mono-varietal), three rice shoots of each cultivar were planted in a pot and plant pattern2 (mixed-varietal), one rice shoot of three cultivars were planted in a pot), △ was used as a tool to analyze gas exchange parameters, dry matter (DM) and grain yield (GY) under different levels of water stress. We found that changes in △ were always consistent with changes in DM, GY and gas exchange parameters under different water supply condition and for all genotypes regardless of planting pattern. In both mixed-varietal and mono-varietal trials, △ at maturity was significantly associated with photosynthesis rate, stomatal conductance, transpiration rate and the ratio of internal CO2 concentration to ambient CO2 concentration. There were also stronger correlations between △ at maturity and DM and GY than between △ at other sampling stages and DM and GY. Based on these results we conclude that △ values at maturity are more accurate predictors for grain yield in rice cultivars grown under mild stress and moderate stress.