The effect of temperature and developmental stage on carbon dioxide exchange of attached 'Royal Gala', 'Fuji' and 'Cripps' Pink' apple fruits.

摘要

In the Western Cape region of South Africa post-bloom spring temperatures can be high, resulting in high fruit respiration rates during a period when carbohydrate supply can be potentially limiting. Chlorophyllous apple flesh tissues exposed to light are capable of assimilating CO₂ diffusing through stomata or lenticels, or re-fixing CO₂ lost through respiration. This could represent a significant contribution to the carbon balance of growing fruits. In this field study, light-saturated net CO₂ assimilation rate (A_max), dark respiration rate (R_d), and light-saturated apparent photosynthetic rate (P_max, the difference between A_max and R_d), were measured at different fruit surface temperatures on attached 'Royal Gala', 'Fuji' and 'Cripps' Pink' apple fruits in the Ceres and Elgin regions (Western Cape, South Africa). Measurements were performed during the cell division stage (20-30 days after full bloom, DAFB) and during the cell enlargement stage (50-60 DAFB) of fruit growth. In all cultivars, P_max and R_d increased, and A_max decreased with increasing fruit surface temperature. After the cell division stage, P_max and R_d decreased and A_max increased with increasing fruit fresh weight. 'Fuji' fruit reached compensation point (A_max=positive due to P_max exceeding losses by R_d) during the mid-season (55 DAFB) at temperatures of up to 30 degrees C, but A_max remained negative at 35 degrees C. 'Royal Gala' almost reached compensation at 20 and 25 degrees C (53 DAFB), but A_max remained negative at 30 and 35 degrees C. The rapid increase in dark respiration rate with increasing temperatures during the cell division stage of fruit growth creates a high demand for assimilates and could have serious implications for fruit growth and final size in warm climates such as the Western Cape.