Effect of Nitrogen Fertilization on Leaf Chlorophyll Fluorescence in FieldGrown Winter Wheat Under Rainfed Conditions

The effect of nitrogen fertilization on leaf chlorophyll fluorescence was studied in field-grown winter wheat during grain filling under rainfed conditions in Loess Plateau. Results showed that the actual photochemical efficiency of PS Ⅱ reaction center (Ф PS Ⅱ) decreased significantly as leaf water stress progressed, however, the Ф PS was increased by nitrogen fertilization. The Ф PS Ⅱ of 0, 90 and 180 kg ha-1 nitrogen treatments at noon were 0.197, 0.279 and 0.283, respectively, which decreased by 57.7, 56.4 and 40.2% as compared was even higher than that in the moming. Application of nitrogen fertilizer significantly increased maximum photochemical efficiency (Fv/Fm), photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qNP). These results indicated that application of nitrogen fertilizer could increase the light energy conversion efficiency, the potential activity of photosynthetic reaction center, and the non-photochemical dissipation of excess light energy, which can prevent leaf photosynthetic apparatus from damage of treatments, indicating that the excess nitrogen was unfavorable to photosynthesis.