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

We used (CO2)-C-13, tracing and source-sink manipulation to determine if fruiting shoots of peach (Prunus persica (L.) Batsch) trees are autonomous or if they import carbon from neighboring shoots, and if the degree of shoot autonomy is influenced by the source-sink relationship of 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 enhance or inhibit movement of carbon from C-13-labeled fruiting shoots (LFS) to adjacent non-labeled shoots (NLFS), both located within 10 cm on the same main scaffold of V-shaped peach trees. At Stages I and III of fruit growth, fruit and shoot tips were sampled from LFS and NLFS to determine C-13 percentage on the 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, no C-13 was found in fruits or shoot tips of NLFS. Only at Stage III of 'Redhaven' peach fruit growth (2005) was C-13 detected in fruits of NLFS, but only in the treatment favoring movement, and on the day of labeling. When LF was altered to the maximum extent possible and branches were girdled at their base (complete sink removal, 2006), a detectable concentration of C-13 was recovered in fruits of NLFS at both growth stages, indicating that C-13 movement across adjacent shoots is possible, and detectable by C-13 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.