Changes in Leaf Photosynthetic Rate and Respiration Rate with Leaf Age

1. Photosynthetic rate and respiration rate: The photosynthetic rates of one- and two-year-old leaves were relatively close, and their photosynthetic capacity was the strongest, while the photosynthetic rate of three-year-old leaves decreased markedly. The respiration rate showed the same pattern of change, with only three-year-old leaves showing a relatively lower decrease in respiration. 2. Other physiological changes: Measurements of rubpc activity showed that two-year-old leaves were slightly higher than one-year-old leaves, but three-year-old leaves decreased markedly; glycolate oxidase activity was basically similar in one- and two-year-old leaves, and decreased significantly in three-year-old leaves; protein content was higher in one-year-old leaves than in two-year-old leaves, and higher in two-year-old leaves than in three-year-old leaves; chlorophyll content increased with leaf age. The results indicate that one- and two-year-old leaves are functional leaves, while three-year-old leaves have begun to senesce. (Ye Qingsheng, Pan Ruichi)