Carbon autonomy of peach shoots determined by 13C-photoassimilate transport

We used 13CO2 tracing and source-sink manipulation to determine whether fruiting shoots in peach (Prunus persica L. Batsch) trees are autonomous or may import carbon from neighboring shoots, and whether the degree of autonomy is influenced by the source-sink relationship on the shoot. In three experiments, leaf to fruit ratio (L:F) of selected fruiting shoots was moderately (2005 and 2006) or strongly (complete sink removal, 2006) altered to either favor or disfavor movement of carbon from 13C-labeled shoots (LFS) to adjacent non-labeled shoots (NLFS), both located within 10 cm on the same main scaffold of V-shaped peach trees. At stage I and III of fruit growth, fruit and shoot tips were sampled from LFS and NLFS for determination of 13C percentage on the same day of labeling and after one week. Factors that differed among the three experiments in the two years were cultivar, tree age, source-sink ratios, and labeling time. In all cases but one, 13C was not found in fruits or shoot tips of NLFS. Only at stage III of 'Redhaven' peach fruit growth (2005), 13C was detected in fruits of NLFS, but only in the treatment favoring movement, and on the same day of labeling. When L:F was altered to the maximum extent possible and branches were girdled at their base (complete sink removal 2006), a detectable concentration of 13C was recovered in fruits of NLFS at both growth stages, indicating that 13C movement across adjacent shoots is possible and detectable by 13C tracing. According to our results peach branches are relatively autonomous even at the fruiting shoot level. However, conditions of strong imbalance between source supply and sink demand, either experimentally imposed or during periods of strong sink competition, may cause some movement of carbon among neighboring shoots.