Characteristics of organic acid and amino acid in root exudates of rice genotype with high nitrogen efficiency

Nitrogen plays important roles in promoting plant growth and development. The purpose of this study was to investigate how N nutrient affect the changes in the root exudates under different nitrogen levels and their relations with nitrogen utilization efficiency of rice nitrogen efficiency genotype. In this research, a hydroponic experiment was carried out in a net room on the farm of Sichuan Agricultural University, Sichuan province, China in 2009, with four nitrogen fertilizer applications, 10 mg/L, 20 mg/L, 40 mg/L and 60 mg/L. The results show that the nitrogen accumulations of the rice nitrogen efficiency genotype significantly are decreased with the nitrogen level decrease at the tillering stage and jointing stage, while the nitrogen utilization efficiencies are significantly increased. The nitrogen accumulations of the nitrogen efficiency genotype are 42.9% at the tillering stage and 21.4% at the jointing stage, which are higher than those of the inefficiency genotype under the nitrogen level of 20 mg/L. As the main kind of organic acids of the nitrogen efficiency genotype, the secretion volume of oxalate acid accounts for more than 80% of the total organic acid, and those of acetic acid and citric acid are followed. The secretion amounts of organic acid and oxalate acid are significantly decreased with the nitrogen level decrease at the tillering and jointing stages, and the amounts of acetic acide and citric acid show the same trend at the jointing stage. Under the same nitrogen level, the total organic acid secretion of the nitrogen efficiency genotype is significantly lower than that of the inefficiency genotype. As the main kinds of amino acid of the nitrogen efficiency genotype, the secretion volume of alanine accounts for more than 50% of the total amino acid, and is followed by serine, glutamic, aspartic, phenylalanine, glycine and threonine acids. Total amino acids secretion and all components of amino acid secretion are decreased with the nitrogen level decrease. Under the low nitrogen levels of 10 mg/ L and 20 mg/ L, the total amino acids secretion of the nitrogen efficiency genotype is significantly lower than that of the inefficiency genotype. At the tillering and jointing stages, the total organic acid and oxalate acid are significant or very significant negative correlated with the nitrogen utilization efficiency, and amino acid secretion and aspartic acid as the same. It could be concluded that rice nitrogen efficiency genotype has certain regulation mechanism, which can reasonable allocation in vivo assimilation substance, promote the efficient uptake and utilization of nitrogen in low nitrogen condition.