Internal Leaf Water Status and Transport of Water in Rice Plants1

Rice (Oryza sativaL.) is generally grown continuously submerged in lowland soils and under rainfed conditions in upland soils. The objective of this study was to relate transpiration rate and leaf water potential to relative water content. This information may be useful in predicting the effect of soil moisture stress on growth and yield. Rice variety ‘IR‐8’ was grown in the greenhouse for 50 to 60 days under submergence and N⅓ bar soil matric potential, and then allowed to wilt. The pressure potential of leaves approached zero at a total water potential of about −19.5 bars, corresponding to 0.33 relative water content. Leaves experienced a change in cell elasticity at about 3 bars pressure potential and −10 bars total water potential Transpiration rate decreased with leaf water potential, but it was independent of depletion of soil moisture content above 0.21 and 0.18 for plants grown in submerged and unsaturated soil conditions, respectively. These moisture contents correspond to −0.8 bar and −2.0 bars matric potential. Further depletion in moisture content of both soil moisture regimes resulted in a marked decrease in leaf water potential and in transpiration. Trans. port of water in the rice soil‐plant system was affected more by plant factors under flooded conditions than under unsaturated soil conditions.