Nitrogen application rates affect the photosynthetic characteristics of winter wheat flag leaves. A study on a wheat cultivar found that proper nitrogen levels can increase chlorophyll and carotenoid content, delaying leaf aging. Nitrogen also boosts photosynthetic activity, improving the plant's ability to convert light into energy. The study suggests that applying 180 kg of nitrogen per hectare can enhance grain yield by enhancing photosynthetic pigments and efficiency while reducing leaf aging.