Depletion of stem non-structural carbohydrates supports release of lateral branches from apical control in Quercus mongolica seedlings

Key message Repeated pruning modified non-structural carbohydrate distribution in different organs of Quercus mongolica seedlings. Depletion of non-structural carbohydrates in the local stem released active branches from apical control. Abstract The stored non-structural carbohydrates (NSC) (i.e. sugars and starch) in trees play an important role in metabolism and growth, but their relationship with plant architecture is poorly understood. Mongolian oak ( Quercus mongolica ) is an important economic hardwood species in northeast China, but a lack of apical control during the seedling stage may reduce the potential to grow quality timber. In this research, we quantified the effects of repeated pruning (RP) on morphology, biomass, and NSC dynamics in Mongolian oak seedlings. The RP treatment significantly promoted the growth of terminal shoot by increasing the length of the second flush; however, rapid recovery of lateral branch growth indicated that the capacity for apical control was not enhanced. The RP treatment significantly modified longitudinal NSC distribution pattern in different growth units (GUs) of the stem, with higher NSC reserves in the upper parts of the stem expected to enhance growth potential. The sustained total NSC storage of the whole seedling, together with starch depletion at GU1 of the stem, indicated that both the carbohydrate status of the whole seedling and the local costs of starch are the reasons for maintaining the active branch growth. The quantification of the temporal and spatial variation in sugars and starch concentrations in different tissues improved our understanding of NSC dynamics in Mongolian oak, revealing the potential relationships between carbohydrate status and plant apical dominance in trees.