Abstract:

Nitrogen is the most important input required in rice production although over use of N causes so many environment problems. It is well known that N use efficiency is varied in different rice genotypes. Therefore, it is important to explore and exploit the potential contributing to the N use efficiency. As an integral part of plant organs, rice root plays an important role in absorption and utilization of N from soil and fertilizer. In this research, a field experiment with 225 kg ha-1 N fertilizer application was carried out in 2006 on the farm of Yangzhou University, Jiangsu province, China. A total of 12 rice genotypes ( 6 N-efficient and 6 N-inefficient ) selected from 120 rice cultivars grown in Yangzhou during 2004 and 2005 were adopted to investigate the charac-teristics of root morphology and physiology in rice types with different N use efficiencies. Relationship between N use efficiency and indexes of root morphology and physiology was also analyzed. The results showed that at different growth stages, the indexes of root morphology and physiology including the root dry weight, root volume, total absorbing surface area of root, active absorbing surface area of root, ratio of active absorbing surface area to total absorbing surface area in N efficient rice type were obviously higher than those in N inefficient rice type. At the critical stage of productive tillering and the stage of elongating, the ratio of root to shoot in N efficient rice type was significantly higher than that in N inefficient rice type while the trend was con-trary at the stages of heading and maturing. Before the stage of maturing, the root oxidation ability of α-NA in N efficient rice type was superior to that in N inefficiency rice type while at the stage of maturing the root oxidation ability of α-NA in N efficient hybrid rice was appreciably lower than that in some N efficient rice cultivars. N use efficiency positively correlated to all the above morphological and physiological indices at all growth stages, with the exception of negatively correlation to the ratio of root to shoot at the stage of heading and maturing. It could be concluded that the root morphology is good and the root is vigorous in N efficient rice type, its morphological and physiological characteristics ensures the efficient absorption and utilization of N in all its life, and proper ratio of root to shoot and the harmonious growth of root and shoot can also improve the efficiency of N absorption and utilization.

Key words: Rice, N use efficiency, Root morphology, Root physiology, Correlation