Anatomical Variations in Tension Wood of Populus alba under alternate bending, nitrogen fertilization and gibberellin treatments

Poplar is one of the most widely used species in wood and paper industries, and there is a high demand for plantation of this species. Therefore, studying the factors affecting the biometric properties of fibers, anatomy, and physical properties of poplar wood is important. Reaction wood formation (tension wood) in woody plant like poplars is reaction against stress and environmental factors. Tension wood is a rich source of cellulose that can be used for some products including paper or biofuels. The aim of this study was to stimulate the formation of tension wood in two-years-old white poplar (Populus alba) saplings by using alternate bending, nitrogen fertilization (NPK) and inducing gibberellin (G) hormone. Saplings were bended alternately for one month in one direction, and the next month in the opposite direction during the growing season, fertilizer application was applied twice i.e. at the beginning and in the middle of the growing season and gibberellin induction was applied once in the early growing season. Physical and anatomical characteristics of xylem were investigated after the end of the growing season. Studying of specimen transverse section after Safranin/Astra-blue staining showed that in general, alternate bending treatments had more tension wood area in growth ring and ticker gelatinous layer than straight specimens. Alternate bending treatment with NPK+G had a higher wood density, more longitudinal shrinkage, less radial and tangential shrinkage, smaller and less frequent vessels, longer and ticker fibers. The results showed that this treatment was the most effective on the stimulation of the tension wood and the intensity of the formation of the tension wood in these specimens was higher.