Gene Expression, Enzyme Activity, Nitrogen Use Efficiency, and Yield of Rice Affected by Controlled-Release Nitrogen

Controlled- or slow-release urea can improve crop nitrogenuseefficiencies and yields in many agricultural production systems. Theeffect of controlled-release urea on the relationships between levelsof gene expression and yields has not been adequately researched.We conducted a 2 year field study with direct-seeded rice, which includedtreatments of controlled-release urea at four rates (120, 180, 240,and 360 kg N ha(-1)), a standard urea treatment (360kg N ha(-1)), and a control treatment without appliednitrogen. Controlled-release urea improved the inorganic nitrogenconcentrations of root-zone soil and water, functional enzyme activities,protein contents, grain yields, and nitrogen use efficiencies. Controlled-releaseurea also improved the gene expressions of nitrate reductase [NAD(P)H](EC 1.7.1.2), glutamine synthetase (EC 6.3.1.2), and glutamate synthase(EC 1.4.1.14). With the exception of glutamate synthase activity,there were significant correlations among these indices. The resultsshowed that controlled-release urea improved the content of inorganicnitrogen within the rice root zone. Compared with urea, the averageenzyme activity of controlled-release urea increased by 50-200%,and the relative gene expression was increased by 3-4 timeson average. The added soil nitrogen increased the level of gene expression,allowing enhanced synthesis of enzymes and proteins for nitrogen absorptionand use. Hence, controlled-release urea improved the nitrogen useefficiency and the grain yield of rice. Controlled-release urea isan ideal nitrogen fertilizer showing great potential for improvingrice production.