Effects of Nitrogen Fertilization on Dark-Respiration and Growth Efficiency of Field-Grown Rice Plants

摘要

The growth efficiency(GE), specific dark-respiration rate(Rs) and crop growth rate(CGR) of rice plants grown in the field with applications of nitrogen fertilizer at 0, 11 and 17 g per m2 were examined every two weeks in 1996 and 1997. Rs was the highest at the rooting stage, and decreased rapidly until the heading time and gradually thereafter. The nitrogen concentration(NC) of the plant also decreased during ontogeny. NC at each growth stage varied with the amount of nitrogen supply, but Rs did not. This suggests that NC did not directly influence Rs. Alinear relationship was observed between NC and Rs determined for all growth stages as a whole. However, the slope of the NC-Rs regression line greatly varied with the growth stage. The value of GE, CGR/(CGR+R)(R, respiratory loss), was within a range of 60-70% during the early growth stage independent of nitrogen supply, but that during the grain-filling period was lowered by increased nitrogen supply. The nitrogen fertilization increased phytomass and grain yield, accompanied by the increase in respiratory loss. In 1997, a larger amount of carbohydrates was consumed for respiration than in 1996, due to higher atmospheric temperatures during the grain-filling period, and GE at the later stage in 1997 was lower than that in 1996. This means that the increased respiratory loss at high temperatures may be a cause of GE depression.