Varietal differences in leaf water potential, leaf net CO₂ assimilation, conductivity and water use efficiency in upland rice

Abstract

Twenty-eight rice (Oryza sativa L.) genotypes of different origin and habitat were grown in upland culture during the dry season in the Philippines. Irrigation was supplied by overhead sprinklers at a level which kept the crop under continuous mild water stress. Leaf net CO2 assimilation, conductivity, intercellular CO2 concentration, water potential and leaf rolling status were determined on the same leaf of all varieties between 0900 and 1200 hours during the vegetative growth stage.Leaf water potential ranged from -0.8 and -1.3 MPa, with japonica types showing the highest values, AUS types from Bangladesh, the lowest, and indica types intermediate. Leaf conductivity and leaf rolling did not differ significantly among these groups. Most cultivars showed a logarithmic relationship between net CO2 assimilation and conductivity. AUS cultivars had the lowest rates of leaf CO2assimilation, but no differences were observed between japonica and indica varieties. At a given intcercellular CO2concentration, net CO2 assimilation was lowest in AUS varieties, resulting in low water use efficiency, and possibly indicating a higher CO2 compensation point for AUS than for other rice types.