Development of Shoot Architecture of Ligustrum japonicum Thunb. in Response to Soil Moisture

Bud outgrowth dynamics and their implications for shoot architecture were examined in plants under well-irrigated (SC) and water-limitation (LC) conditions.  Plants of Ligustrum japonicum from 11.4 L containers were transplanted into elevated rhizotrons.  Treatments consisted of two irrigation frequencies, once a week for 10 minutes (12 L of water, long wet/dry cycle - LC) and every other day for 5 minutes (6 L of water, short wet/dry cycle - SC), with 12 replications each.  Growth of shoots was monitored weekly. Plants were not pruned.  Neoformed buds had limited sensitivity to dormancy, while preformed buds required more than one growing season to outgrow naturally.  First spring shoot flush was mostly due to lateral bud outgrowth, while latter flushes had prominent contributions of neoformed apex bud outgrowth.  First-order terminal branches had mainly determinate growth.  First-order lateral branches had increased occurrence of indeterminate growth.  Water limitation influenced shoot architecture by enhancing apical dominance.  Lateral branching was diminished 51% in LC plants compared with SC plants.  As plants adapted to imposed stress by additional root growth, indeterminate growth was triggered more often in meristematic regions of terminal buds.  Old buds burst more frequently than the newly formed apex lateral bud of stressed plants after substantial root growth.  Plants under SC had relatively uniform and compact canopies, while plants under LC had considerably less new branches, which were mostly excessively long that would require pruning.