Genotypic variation in morphological and physiological characteristics of rice (Oryza sativa L.) under aerobic conditions

The aerobic rice system is a new promising water-saving cultivation technique; however, rice sensitivity to aerobic conditions limits its use. We investigated morphological and physiological responses of seedlings of two upland rice genotypes (Beodien and Sensho) and two lowland rice genotypes (KD18 and Koshihikari) to flooded condition (control) and three aerobic conditions (32, 22, and 14% soil moisture content (SMC), w/w) in 2013 and to a flooded condition and aerobic condition (32% SMC) in 2014. Under aerobic conditions, shoot growth was limited because of a reduction in water uptake. Water uptake capacity was highly controlled by root traits such as root dry weight and root length. Under aerobic conditions, leaf water potential, stomatal conductance, and root hydraulic conductance declined. We found that the 32% SMC condition was the most favorable aerobic condition whereas 22% and 14% SMC conditions strongly suppressed rice growth. Genotypic variations in physio-morphological traits were more clearly detected under wellirrigated conditions (32% SMC) than other two aerobic conditions. In both years, cultivar Sensho adapted to the 32% SMC condition, whereas Koshihikari did not adapt to the aerobic rice system, probably because of its limited root growth and lower root plasticity. The positive correlation between root traits and water uptake indicate that root traits are important for improving rice performance under an aerobic rice system.