Photosynthetic physiological characteristics of rice varieties with high nitrogen use efficiencies

【Objective】The study aimed to explore photosynthetic physiological characteristics of rice varieties with different N-use efficiencies.【Method】The hydroponic culture experiment was carried out to analyze changes of physiological and agronomic traits and photosynthetic characteristics of 4rice varieties with high N-use efficiencies and 4varieties with low N-use efficiencies under normal nitrogen(1N)and low nitrogen(1/12N)levels after heading.【Result】At low nitrogen level,the chlorophyll contents,nitrate reductase activity,soluble protein contents,dry-weight of aboveground,plant height,root length,net photosynthetic rate(Pn),apparent mesophyll conductance(AMC)and water use efficiency(WUE)of high Nuse efficiency rice varieties were significantly higher than those of low N-use efficiency rice varieties,but they had no significant difference in each index at normal nitrogen level.Percentages of stomatal limitation(Ls)and root length of high and low N-use efficiency rice varieties increased with low nitrogen level,but other indexes all declined.【Conclusion】At low nitrogen level,the decline of Pn was caused by non-stomatal limitation,which may be related to decrease of RuBP-Case activity.Physiological indexes of high N-use efficiency rice varieties were higher than those of low N-use efficiency rice varieties,indicating that high N-use efficiency rice varieties could better adapt to low nitrogen environment,and low nitrogen condition is conducive to root growth.