[Effects of long-term application of nitrogen fertilizer on leaf chlorophyll fluorescence of upland winter wheat].

The effects of long-term nitrogen fertilization of chlorophyll fluorescence of winter wheat at its grain-filling stage on Loess Plateau highland were studied. The results showed that the actual photochemical efficiency of PS II reaction center (phi PS II) was decreased with leaf water stress aggravated, while was increased by nitrogen supply. The phi PS II of 0 kg.hm-2, 90 kg.hm-2 and 180 kg.hm-2 nitrogen treatments at noon were 0.197, 0.279 and 0.283, which decreased by 57.7%, 56.4% and 40.2% compared to that of morning, respectively. While they were all resumed at afternoon, even it was higher, for 180 kg.hm-2 nitrogen treatment, than that of morning. Maximum photochemical efficiency (Fv/Fm), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qNP) were also increased by nitrogen supply, showing that the light energy conversion efficiency, and potential activity of photosynthetic reaction center and the non-photochemical dissipation of excess light energy, which resisted the damage on photosynthetic apparatus of environmental stress, were improved. No significant difference was found between 90 kg.hm-2 and 180 kg.hm-2 N treatments, which indicated that excess nitrogen was not favorable to photosynthetic performance, and photosynthetic capacity was not improved in proportion with nitrogen supply.