عنوان مقاله [English]
Background and objectives: Raw materials shortage is one of the main challenges of wood and paper industry of Iran. According to the laws restricting forest harvesting, tree farming as an alternative source of wood supply should be focused. On the other hand, due to limited water resources in Iran and high water demand of poplars, there are increasing efforts to introduce poplar species with higher drought tolerance. However, these researches are mainly concentrated just on the volume production or tree surviving and resulting wood quality was less investigated. In one of such studies, growth characteristics of different species/clones of Populus were investigated in different irrigation intervals (4, 8, and 12 days) and it was concluded that there was not a significant difference between the 4 and 8 days intervals in respect of growth parameters. However, the probable effect of these two irrigation intervals on wood quality remained unknown. Hence, the rationale of current study was to investigate the effect of 4 and 8 days irrigation intervals on wood and fiber characteristics of two superior poplar clones. In addition, the relation between wood quality and irrigation was discussed from the physiological points of view.
Materials and methods: Pith-to-bark cores were taken from two elite poplar trees (Populus euroamerican and P. nigra) using increment borer. Wood anatomical features and fiber biometry of the last five tree rings including tree-ring width, vessel size and length, and fiber length, diameter and cell wall thickness were studied.
Results: The results showed that the effect of irrigation intervals was statistically significant on tree-ring width, vessel diameter and length and fiber wall thickness but not significant on fiber length and diameter. In both species, increasing irrigation intervals from 4 to 8 days, led to a decrease in ring width. Nonetheless, the type of species influenced the reduction rate: P. nigra trees were less sensitive to irrigation intervals and their ring widths were less reduced. Moreover, it was shown that radial growth and fiber length of poplars (as two important applied properties) are separately influenced by different components.
Conclusion: Overall, it can be concluded that in the case of P. euroamerican, if the wood anatomical features were of importance, there is no difference between 4 and 8 days irrigation and even longer interval of irrigation yields superior characteristics (e.g. longer fibers). Hence, for saving water resources, 8 days irrigation is recommended. This conclusion is also roughly applicable for P. nigra since the reduction in fiber length of this species after longer irrigation periods is not remarkable and therefore doesn’t justify the shorter irrigation intervals. Finally, since radial growth rate and fiber length are influenced by different factors and are less related to each other, both features can simultaneously be enhanced with a proper management.