Effect of drought, fertilization, wounding and bending treatments on lignin content and composition of eucalyptus seedlings (Eucalyptus camaldulensis)

In this study, the effects of drought, fertilization, wounding and bending treatments were investigated on the content and composition of wood lignin in two-year-old eucalyptus seedlings (Eucalyptus camaldulensis). Results showed that drought-induced xylem had the highest concentration of lignin and guaiacyl (G) units and the lowest amount of hydroxyphenyl (H) and syringyl (S) units as well as the lowest S/G ratio compared with other treatments. In contrast, the lowest concentration of lignin and G units and the highest amount of S units and the highest S/G ratio were observed in fertilization treatment. Due to this treatment, H units increased. After wounding, lignin concentration did not change significantly compared with the control treatment and only slightly decreased. However, as a result of this treatment, G units increased significantly and H and S units and S/G ratio decreased. The most important chemical change observed in bending treatment was a sharp increase in H units and a decrease in guaiacyl and syringyl and an increase in the S/G ratio. Overall, it can be concluded that the chemistry of xylem is altered to give the plant the best ability to withstand environmental stresses. Guaiacyl lignin has a more protective role, and increased H lignin is associated with increased growth rate or increased stem flexibility.