Difference between NH2 + and NO2 - uptake kinetics of different rice (Oryza sativa L.) grown hydroponically

To investigate the uptake kinetic difference between NH4+ and NO3- when both of them are present together, a set of 23 rice varieties with different nitrogen use efficiencies was grown hydroponically. Maximum uptake rate per pot (V-m), Michaelis-Menten constant (K-m) and maximum uptake rate per dry weight of root (V-max) for NH4+ and NO3- were determined at two N-levels, i.e. N 10 mg L-1(N-10) and 40 mg L-1 (N-40), and growth stages (40 and 58 days after sowing referred as DAS(40) and DAS(58)). The results showed that V-m and V-max for NH4+ of all tested varieties were greater than for NO3- both N-levels and stages, while greater V-m for NH4+ than for NO3- was ascribed to greater Similarly, most of the varieties had greater K-m for NH4+ than for NO3- at both N-levels and stages, however, the number of varieties which had higher K-m for NH4+ than for NO3- was 21 at N-10, and 14 and 19 under N-40 at 40 and 58 DAS, respectively. The relationship between V-m and K-m for NH4+ was significantly negative. The greater V-m can be mainly attributed to large root system at higher N level, e.g. dry weight of root (DWR) contributed approximately 70% to V-m for NH4+ and NO3- at N-40, while at lower N level (N-m) the higher V-m mainly ascribed to the presence of more transporters for NH4+ than for NO3+, though the affinity for NH4+ of rice was less than for NO3-. All these results indicate that rice plant possesses higher uptake ability for NH4+ than for NO3-, and can adapt to high and low NH4+ habitats simultaneously. These findings may provide new insights to improve the uptake efficiency of rice for NH4+ and NO3- through improved V-max and by considering the large root system and lower K-m for NH4+ and NO3-.