Abstract: The formation of wood is affected by the growing season and the environment. Ring-porous tree species have distinct earlywood-latewood differences. However, it is not clear how earlywood and latewood respond to drought and the differences in adaptation. Therefore, based on the analyses of phenology, growth, and xylem development over a year, xylem development in Fraxinus mandshurica was divided into earlywood, transition, and latewood stages. Variation patterns of 38 wood indices from 31 genotypes indicated that the formation of wood tissues was inhibited, and the proportion of xylem cells was affected by drought at each stage. However, soluble sugar affected osmotic regulation only during drought across earlywood and transition stages. To maintain water and nutrient transport during drought and to resist embolism risk, drought in the earlywood stage leads to varying degrees of earlywood vessel diameter reduction, with pits enlarging to compensate. In contrast, during the latewood stage, drought causes latewood vessel diameter to increase and pits to shrink accordingly. In addition, the results indicate that several wood indices correlate with drought resistance at each stage, but earlywood vessel diameter, soluble sugar, and latewood vessel diameters exhibited the strongest correlations in the earlywood, transition, and latewood stages. These findings provide clues to understanding plant survival strategies under drought stress and are of significance for plant ecology research on the growth and adaptation of tree species under climate change.

Key words: Drought, Vascular system, Wood development, Ring-porous wood