The study looked at how different amounts of nitrogen fertilizer affected the growth and photosynthesis of a hybrid citrus plant called 'Huangguogan'. They found that adding more nitrogen helped the plant grow better, up to a certain point. The best growth was seen with 120 grams of nitrogen per year. More nitrogen also increased the plant's ability to photosynthesize, but only up to that 120-gram limit. After that, adding more nitrogen didn't help as much. The researchers also saw that the amount of chlorophyll in the leaves was linked to how much nitrogen was in the leaves. This information can help farmers know how much nitrogen to use on their 'Huangguogan' orchards for the best results.