Physiological and metabolic responses to nitrogen availability of rice (Oryza sativa L.) cultivars with differ in nitrogen efficient

Developing genotypes with high-nitrogen use efficiency is a prerequisite for achieving sustainable agriculture and high yields. In this study, both physiological and metabolic analyses were performed to evaluate the NUE (nitrogen use efficiency) of two elite indica rice cultivars: OM052 and Huanghuazhan (HHZ). The pNUE and gNUE of OM052 were higher than HHZ under three N conditions, and significant (p < 0.05) especially under both LN and MN conditions. The contents of soluble sugar and malate were significantly different between OM052 and HHZ under LN and HN conditions. The GDH activity in OM052 was significantly high than that in HHZ under HN condition. Metabolic analyses showed that 136 and 142 differentially accumulating metabolites were identified between OM052 and HHZ under LN and HN conditions, respectively. KEGG analysis showed that ‘aminoacyl-tRNA biosynthesis’ was also the most significant enriched in LN_OM052 vs. LN_ HHZ and ‘Glyoxylate and dicarboxylate metabolism’ and ‘citrate cycle’ were the most significantly enriched in HN_OM052 vs. HN_ HHZ. The contents of four metabolites (cis-aconitate, isocitrate, fumarate, and malate) involved in the TCA cycle were significantly upregulated in HN condition compared with LN condition, regardless of OM052 and HHZ. Taken together, the results of our study revealed the physiological and metabolic differences underlying the OM052 and HHZ and provide new insights into coordinating C and N metabolism and improving the NUE of rice.