LAUSR

Although pruning is important to obtain high-quality, large-diameter timber, the effects of pruning on nonstructural carbohydrates (NSC) in aboveground organs of many timber species are not well understood. Three intensities of pruning (none, moderate and severe) were tested on poplars ( Populus alba  ×  P. talassica ) in the arid desert region of northwest China to compare the concentrations of soluble sugar (SS), starch (ST) and total nonstructural carbohydrate (TNC) in leaves, branches and trunks during the growing season. The concentration of NSC components after different pruning intensities varied similarly in seasonal patterns, increasing slowly at the beginning of the growing season, continuously declining in the middle, then gradually recovering by the end of the growing season. The monthly mean NSC concentration in poplar differed significantly among the three pruning intensities ( p  < 0.05). The SS concentration in pruned trees was higher than in unpruned trees ( p  < 0.05). For moderately pruned trees, the concentrations of ST and TNC in trunks and branches were higher than in unpruned and in severely pruned trees ( p  < 0.05). Compared with no pruning, pruning changed the seasonal variation in NSC concentration. The orders of SS and TNC concentrations in aboveground organs were leaf > branch > trunk, while the order of ST concentration was trunk > leaf > branch, which was related to functional differences of plant organs. The annual average growth in height of unpruned, moderately pruned, and severely pruned poplars was 0.21 ± 0.06, 0.45 ± 0.09 and 0.24 ± 0.05 m, respectively, and the annual average growth in DBH were 0.92 ± 0.04, 1.27 ± 0.06 and 1.02 ± 0.05 cm, respectively. Our results demonstrate that moderate pruning may effectively increase the annual growth in tree height and DBH while avoiding damage caused by excessive pruning to the tree body. Therefore, moderate pruning may increase the NSC storage and improve the growth of timber species.