ObjectivesExcessive application of nitrogen fertilizers lead to nitrogen loss and the cost increase of agricultural production. Root morphology is one of main factors that affect absorption and utilization of nutrients by rice. In this study, we investigated the relationship between root morphology and nitrogen uptake and accumulation of rice.

MethodsHydroponic experiments were conducted with 55 rice cultivars to examine relationships between the plant nitrogen uptake and several indices of root morphology using both NH₄⁺-N and NO₃^–-N solution.

ResultsThe correlation coefficients between the nitrogen uptake and root morphology indices when N was supplied as NH₄⁺-N were higher than those when supplied as NO₃^–-N. After the six leaf stage of rice, under the same solution concentration of nitrogen, the average biomass of rice seedlings was 55.77 mg per plant in the NH₄⁺-N solution, which was increased by 4.94 mg per plant compared with the NO₃^–-N solution. The average nitrogen content of rice seedlings was 4.22% when grown in the NH₄⁺-N solution, which was increased by 0.72%, and the average accumulation of nitrogen in the seedlings was 1.91 mg per plant when supplied with the NH₄⁺-N, which was increased by 0.67 mg per plant compared with the NO₃^–-N solution. There were significant differences in the root morphology indices between plants supplied with the NH₄⁺-N and NO₃^–-N under the same concentration. The higher the coefficient of variation of root morphology was, the higher the greater difference between rice cultivars was. The root branch number was most highly correlated with the root morphology indices, whereas the mean root diameter was the least correlated. These differences reflected that there was a larger variation in root branching values, and less variation in mean root diameters among the 55 rice cultivars. The total root volume, total root area, total root length and branching number were significantly correlated with biomass, nitrogen content, and nitrogen accumulation in rice plants at the seedling stage, and the correlation coefficients were in order: the total root volume > the total root area > total root length > the number of branches. The correlations between the nitrogen uptake and the indices of root morphology when plants were supplied with NH₄⁺-N were higher than those when supplied with NO₃^–-N.

ConclusionsThe total root volume, total root area, total root length, and the number of branches may be important indicators for evaluating the nitrogen use efficiency of rice at the seedling stage.