Effect of Prebloom Pruning on 13C and 15N Distribution during Early Spring in Sweet Cherry

In sweet cherry, highly advanced dwarf combinations using 'Gisela' rootstocks promote higher productivity than do more vigorous combinations but require maintaining the leaf area to fruit area (LA:F) ratio. An experiment using double isotopic enrichment with C-13 and N-15 was carried out in 5-year-old 'Bing'/'GI 6' trees in a commercial orchard located in Santa Cruz, Chile (34 degrees 39'S; 71 degrees 19'W), and characterized by a Mediterranean climate. Forty whole sweet cherry trees (TR1) trained as central axes were pruned in winter [July 20, 60 days before full bloom (DBFB)] and another 40 trees were left without pruning (TR2). A single (CO2)-C-13 pulse and N-15-urea application to the mature leaves of individual 4-year-old branches on trees of both TRs was carried out during stage III (SIII). Winter pruning reduced yield by 44%, improved fruit quality [i.e., size, weight, and soluble solids content (SSC)] and induced the growth of extension shoots (ES) (i.e., number, length, and LA). For both TRs, fruits were stronger sinks for C-13-photoassimilates and N-15 than were ES. ES of pruned trees had higher sink strength than ES of unpruned trees. Pruned trees developed more ES that were longer and that had higher LA compared with the ES of unpruned trees.