Interaction of nitrogen supply and soil water stress on photosynthesis and transpiration in rice.

The purpose of this study is to determine if there is an interaction of nitrogen nutrition and water stress on apparent photosynthesis (APS), transpiration (Tr), and water-use efficiency in rice (Oryza sativa L.). The potted plants, which were cultured in high and low nitrogen levels, were exposed to the water stress condition, and the gas exchange rates were measured. A significant interaction of nitrogen supply and soil water stress on APS and Tr occurred, with high nitrogen plants being more affected by water stress, in respects of APS and Tr, compared with low nitrogen plants. This high responsiveness of APS and Tr in high nitrogen plants was due to stomatal sensitivity to water stress. In addition, high nitrogen plants maintained better photosynthetic machinery under water stress condition. As the results, it was found that the characteristics of greater stomatal sensitivity and better photosynthetic machinery in high nitrogen plants, led to their higher water-use efficiency.