Effect of Planting Density on Net Production and Partitioning in ‘Starking Delicious’ Apple Trees on Dwarfing and Semi-dwarfing Rootstocks

Abstract

The effect of planting density (330–3178 trees/ha) on net production (t DW/ha/y) and partitioning was studied in 11 to 13-year-old ‘Starking Delicious’ apple trees on M.9, M.26, M.7 and MM.106 without pruning. On all rootstocks, individual annual dry matter production (⊿pn) and annual dry matter production per tree of fruit (fd), leaf (ld), branch (⊿pb), trunk (⊿pt) and root (⊿pr) decreased as planting density (ρ) increased. The density effects on ⊿pn, z (ld, ⊿pb, ⊿pt or ⊿pr) and fd could be represented by the following equations, respectively: 1/⊿pn = A₁ρ + B₁, 1/z = A₂ρ + B₂, and fd = K exp (−kρ). On all rootstocks, net production (⊿Pn) and net production of leaf (Ld), branch (⊿Pb), trunk (⊿Pt) and root (⊿Pr) increased as planting density (ρ) increased, but on three rootstocks excluding M.26, the net production of fruit (fruit production: Fd) was maximized at the optimum planting density (ρ_opt). The density effects on⊿Pn, Z (Ld,⊿Pb,⊿Pt or⊿Pr) and Fd could be represented by the following equations, respectively: 1/⊿Pn = A₃ + B₃/ρ, 1/Z = A₄ + B₄/ρ, and Fd = H´ρ/(A₁ρ + B₁)^h´. Partitioning ratio into leaf (Ld/⊿Pn), branch (⊿Pb/⊿Pn), trunk (⊿Pt/⊿Pn) and root (⊿Pr/⊿Pn) increased as planting density (ρ) increased, but that into fruit (Fd/⊿Pn) decreased. The density effects on Z/⊿Pn (Ld/⊿Pn, ⊿Pb/⊿Pn, ⊿Pt/⊿Pn or ⊿Pr/⊿Pn) and Fd/⊿Pn could be represented by the following equations, respectively: 1/(Z/⊿Pn) = A₅ + B₅/ρ and Fd/⊿Pn = K´ exp (−k´ρ). The relationship between fruit production (Fd) and net production (⊿Pn) could be represented by the following quadratic function: Fd = −a₁(⊿Pn)² + b₁(⊿Pn) + c₁. The relationship between fruit production (Fd) and partitioning ratio into fruit (Fd/⊿Pn) could be represented by the following quadratic function: Fd = −a₂(Fd/⊿Pn)² + b₂(Fd/⊿Pn) + c₂. The relative relation between the net production (⊿ Pn) and the partitioning ratio into fruit (Fd/⊿ Pn) was defined as ⊿ Pn/(Fd/⊿ Pn), and the relations between fruit production (Fd) and ⊿ Pn/(Fd/⊿ Pn) plotted on the log~log coordinates (Fig. 6) showed the same pattern as the log Fd~logρ curves (Fig. 2). From these results, it was suggested that the density effect on fruit production is a phenomenon that ⊿Pn/(Fd/⊿Pn) changes with planting density, and, as a result, fruit production changes.