Anatomical Features and Its Radial Variations among Different Catalpa bungei Clones

Research highlights: Annual wood anatomy (xylem) aids our understanding of mature wood formation and the growth strategies of trees. Background and Objectives: Catalpa bungei is an important native species in China that produces excellent quality wood. Herein, we clarified the effects of the genetic origin and cambial age on the anatomical characteristics of C. bungei wood. Materials and Methods: Six new 13-year-old C. bungei clones: ‘1-1’ (n trees = 3), ‘1-3’ (n trees = 3), ‘2-7’ (n trees = 3), ‘2-8’ (n trees = 3), ‘8-1’ (n trees = 4), and ‘9-1’ (n trees = 3) were removed for study from a plantation in Tianshui City, Gansu province, China. Xylem features were observed and the anatomical variables were manually measured via image analysis on (macro- micro-, and ultra-) features cut from radial increments of earlywood and latewood sampled at breast height. Results: Between the age of 1 and 2 years, wood was diffuse-porous; between the age of 3 and 9 years, wood was semi-ring-porous; and between the age of 10 and 13 years, wood was ring-porous. The effect of clones on anatomical characteristics was significant except for the microfibril angle in latewood and ring width. The transition between juvenile and mature wood was between 7 and 8 years based on patterns of radial variation in fiber length (earlywood) and microfibril angle. From the pith to the bark, fiber length, double wall thickness, fiber wall: lumen ratio, vessel diameter in earlywood, proportion of vessel in earlywood, and axial parenchyma in latewood increased significantly, whereas ring width, earlywood vessels, and the proportion of fiber decreased significantly. In addition, other features, such as vessel length, microfibril angle, and ray proportion, did not differ significantly from the pith to the bark. Conclusions: Breeding program must consider both clone and cambial age to improve the economic profitability of wood production.