Direct assimilation of atmospheric carbon by immature apple fruits

Although fruit development primarily depends on photoassimilation by leaves, immature green fruits can also directly assimilate atmospheric CO₂. To elucidate the process of C accumulation due to direct assimilation by fruit, we conducted a ¹³CO₂ exposure experiment in an orchard in late June with immature 'Fuji' apples (Malus domestica). Four fruits from three trees were enclosed in transparent plastic bags and exposed to ¹³CO₂ using an in-situ exposure system. Fruits were collected prior to and immediately following exposure in early July, late September and mid-November, and ¹³C concentrations in the peduncle, skin, flesh and core (including seeds) were measured. The higher assimilated ¹³C concentrations measured following exposure indicated that the fruits directly assimilated atmospheric ¹³C. The ¹³C concentration in fruit skin was higher immediately after exposure and in early July compared with that prior to exposure. In late September and mid-November, ¹³C concentrations were close to natural levels (authors)