2020 年 76 巻 1 号 p. 11-18
Nitrogen use efficiency (NUE), defined as the ratio of biomass growth and the nitrogen (N) taken up from a soil, is widely used in the evaluation of plant N economy. We conducted a fertilization experiment with Quercus serrata seedlings under different soil N and phosphorus (P) levels to determine the influence of high N deposition levels under different P availabilities upon NUE, plus the NUE components N productivity (NP), and mean residence time of N (MRT). The seedlings were grown for one growing season in the potted soil under three N levels (0, 50, and 100 kg N ha-1) combined with two P levels (0 and 50 kg P ha-1). Nitrogen supply to the soil reduced NUE by decreasing NP and MRT, whereas P supply enhanced NUE. Although P supply did not have a significant influence on the reduction of NUE with increasing N levels, it affected the response of the NUE components with increasing N levels. Within leaves, N supply reduced the photosynthetic nitrogen use efficiency (PNUE), P alleviated this reduction. Therefore, P is considered as one of the key factors determining the change of NUE in Q. serrata under the influence of high N supply.