Abstract
The optimization of nitrogen (N) application level and the development of cultivars with high physiological N use efficiency (NUE) are needed to establish a sustainable rice cropping system. In our previous study, we found that a strain of wild rice species Oryza nivara (IRGC105715; NVR) shows high NUE under low N conditions. In this study we investigated photosynthetic traits of NVR in comparison with the O. sativa japonica cultivar Nipponbare. Plants were water-cultured under three N conditions; standard N (1N), medium N (1/2N) and low N (1/4N) levels. At the vegetative stage, leaves of NVR showed a higher photosynthetic rate, stomatal conductance (Gs) and CO2 fixation activity than those of Nipponbare under 1/2N and 1/4N conditions. NVR also showed higher maximum quantum yield of photosystem II than Nipponbare under 1/4N condition. NVR tended to have higher specific leaf weight and leaf N content than Nipponbare. Under 1/2N and 1/4N conditions, NVR exhibited higher photosynthetic N use efficiency (PNUE) than Nipponbare. These data demonstrate that NVR have higher photosynthetic capacity and PNUE than Nipponbare under low N conditions. These traits may be attributed to the maintenance of higher Gs, photochemical activity and leaf N content under a low N condition in NVR. It is suggested that the photosynthetic properties of NVR may be a promising genetic trait for breeding of cultivars suitable for low N-input agriculture.
