Nitrogen form differently modulates nitrogen uptake and utilization and related gene expression between two tea cultivars

Nitrogen (N) is essential for the growth and development of tea plants, and ammonium (NH4+) and nitrate (NO3-) are crucial N sources for tea yield and amino acid contents. However, the uptake and utilization of different N forms in tea plants are different. Reasonable N form is an important means to enhance the growth and development of tea plants. Therefore, supplying suitable N forms may be effective way to optimize N use efficiency. A hydroponic trial was conducted with 'Chuancha No.2′ (CC) and 'Emeiwenchun' (EW) tea cultivars with N form treatments: NH4+ and NO3-. The results showed that there were significant difference in the NH4+/NO3- uptake kinetics, dynamic changes in 15N abundance, enzyme activities, and related gene expression in N metabolism between CC and EW after NH4+/NO3- treatment. In CC and EW, NH4+ and NO3- uptake followed Michaelis-Menten kinetics at low N concentrations (< 1 mmol l-1), but CC exhibited a slightly higher uptake rate than EW when supplied with 2 mmol l-1 NH4+. In a 0–24 h 15N tracing experiment, CC roots accumulated 15N faster than EW under NH4+. NH4+-fed CC exhibited higher GS activities and higher expression levels of CsAMTs and genes involved in N utilization, such as CsNR, CsGS2, CsGDH1, and CsTS1, compared to EW. When NO3- was provided, EW roots accumulated more 15N than CC roots from 8 to 24 h, which could be attributed to the higher NR activities and higher expression levels of CsNRT1.5, CsNR, CsGS1.1 and CsGS1.2 than those in CC. In summary, the two tea varieties exhibited distinct characteristics of N uptake and utilization, as well as gene expression patterns under NH4+/NO3- treatments. CC demonstrated an advantage in NH4+ uptake and assimilation, while EW exhibited an advantage in NO3-.