Advanced imaging and quantification of the cambium and developing xylem in eucalypts using X-ray micro- and nano-computed tomography

In recent years, the popularity of X-ray computed tomography (CT), as a non-destructive imaging technique, has continued to expand in various research domains. In wood research, X-ray CT has proven to be useful for three-dimensional (3D) structural studies investigating the complex tissues of trees. Wood formation (i.e., xylogenesis) initiates in the cambium and a narrow zone of subsequent differentiation, both of which play key roles in plant growth and development. However, the dynamics of xylogenesis in eucalypts remain relatively poorly understood, in large part due to challenges in sampling, imaging, and characterizing the cambium. Therefore, the aim of this study was to present a workflow to evaluate the feasibility of using X-ray CT to characterize and quantify the structural properties of the cambium in eucalypts. The growth responses of Corymbia hybrid seedlings, exposed to either irrigated or droughted conditions, was investigated by monitoring the structural development of the cambium. To track microstructural changes in the cambium, the same seedlings were imaged with X-ray micro-CT (μCT) one day before the treatments and again six days after the respective treatments. After the last X-ray μCT scan, X-ray nano-CT was also applied. Using image analysis techniques, the morphological characteristics of the cambium could be determined. X-ray μCT displayed a larger, thicker cambial zone in irrigated plants, while a much thinner cambium was visible in droughted seedlings. X-ray nano-CT revealed that droughted plants were associated with a significantly () smaller cambium volume containing smaller cells, compared to the cambium of irrigated plants. Light microscopy was used to validate the CT results and demonstrated no significant () difference in the cambium width and cell diameter obtained from the two respective CT techniques. The findings of this study proved X-ray CT to be a valuable tool for examining the effect of changing environmental conditions on the complex cambium structure of Corymbia hybrid seedlings.