Chemical variations in tension wood of poplar tree induced by intermittent bending, fertilizer and hormone treatments

Abstract

Tree growth is influenced by various environmental factors that lead to anatomical, physical and chemi cal changes in their wood. Reaction wood is one of the tree’s reactions that make many restrictions in wood usages. Reaction wood in broadleaf is called tension wood. This study was aimed to stimulate the formation of tension wood in two-year-old seedlings of Populus alba by using intermittent bending, nitrogen fertilization and gibberellin hormone. The application of different treatments increased the content of cellulose compared to the control sample. Meanwhile, the bent specimens had more increase while the straight specimens had no significant difference in the statistical grouping. The content of lignin decreased in all treatments compared to the control sample. The cellulose/lignin ratios obtained from ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) analysis of wood sawdust and chemical composition measurements were almost close to each other and were higher in the treated samples than in the control. The degree of crystallinity obtained from XRD (X-ray Diffraction) measurements showed that all samples under intermittent bending had a greater effect on the stimulation and changes of chemical properties of tension wood in poplar and the appli cation of nitrogen fertilization and gibberellin hormone increased this effect. The formation of gelatinous layer in the innermost part of the intermittent bent seedlings fiber cell wall was visible in light microscope images. the ratio of cellulose to lignin in the treated samples was higher than the control samples but the differences in saw dust ratios were not significant. Straight treatment + NPK + GA3 in wood sawdust samples and intermittent bending treatment in cross-sectional samples with 2,15 and 3,69 showed the highest cellulose to lignin ratio, respectively. These results are slightly different from the ratios obtained from the measurement of wood com pounds by chemical methods, but in both chemical analysis and ATR-FTIR method the treated samples showed higher cellulose to lignin ratio than the control sample. These observations show the effect of bending and NPK fertilizer treatment more strongly and also GA3 treatment on reducing lignin content and increasing cellulose and stimulating the formation of tension wood. Pitre et al. 2007b and Pitre et al. 2010 obtained similar results in relation to bending and NPK fertilizer treatment.