Carbon Exchange Rate and Accumulation in Limbs of Fruiting and Nonfruiting Apple Trees

Abstract

Mature `Sturdeespur Delicious' apple (Malus domestica Borkh.) trees on MM.106 rootstocks were hand-deblossomed or hand-pollinated in 1989 and 1990. Two representative limbs were chosen at bloom on each tree in 1989, one of which was girdled (G) while the other served as a control. One representative limb was selected at bloom in 1990. Three leaf types were studied: shoot (SH) leaves, leaves on nonfruiting (NF) spurs (S-F), and leaves on fruiting (F) spurs (S + F). The presence of fruit did not affect C exchange rate (CER). Girdling fruiting limbs reduced CER by ≈10%. Girdling NF limbs resulted in starch accumulation in the leaves and low CER. SH leaves had the highest CER per unit leaf area, while S + F leaves had the lowest. Total seasonal dry weight (DW) accumulated in leaves, fruit, and wood, normalized per square centimeter limb cross-sectional area (LCSA), was higher in F trees. Roots were longer and DW of roots extracted from soil core samples was higher in NF trees. NF trees had significantly more vegetative growth in new shoots and dry-matter increment in wood than F trees.