Abstract: This paper studied the effects of different NO₃^- concentration on the photosynthetic rate, photochemical efficiency, and absorbed light energy allocation in cucumber seedling leaves. The results indicated that when the available NO₃^- concentration in the medium was low (14-98 mmol NO₃^-·L^-1),an appropriate supplement of NO₃^- could enhance the capability of cucumber leaves in capturing light energy, and promote the photosynthesis. However, with further increase of NO₃^-, the photochemical efficiency of PSⅡ decreased, electron transfer restrained, and net photosynthetic rate as well as the absorbed light energy used in photochemical reaction of PSⅡ decreased. At the same time, the light energy used in antenna heat dissipation increased, while the photochemical efficiency decreased. After treated with 140 and 182 mmol NO₃^-·L^-1 for 6 days, the photosynthetic rate (P_n) was decreased by 35% and 78%, respectively, maximal PSⅡ efficiency at open centers in the absence of NPQ (F_v/F_m), antenna efficiency at open centers in the presence of NPQ(F_v’/F_m’), actual PSⅡ efficiency (Φ_PSⅡ) and photochemical quenching (q_P) were lower, non-photochemical quenching (NPQ) was higher, and the deviation from full balance between PSⅠ and PSⅡ (β/α-1) was improved significantly, compared with the control. The fluctuant ranges of these chlorophyll fluorescence parameters were increased at higher NO₃^- concentration, compared with those at lower NO₃^-concentration. The absorbed light energy allocated to the photochemical reaction of PSⅡ (P) was reduced by high light intensity and high NO₃^-concentration. Meanwhile, the proportion allocated in antenna heat dissipation (D) increased significantly. Antenna heat dissipation was the main way for excessive energy dissipation.

Key words: Tibet, Beijing, Wheat, Planting in the different location, Quality variation