the effect of water deficit on growth and some physiological responses of yew (taxus baccata l.), as an ornamental tree

Drought is the most important environmental stress, which is usually defined as an external factor that has adverse effects in plants. the endangered yew species is very important for human societies for medicinal and ornamental reasons. the roots and leaves of this plant produce biochemical compounds such as flavonoids, alkaloids and tannins that act as anti-inflammatory, anti-cancer, anti-bacterial and anti-viral. the present research investigated the effect of different levels of drought stress (100, 75, 50 and 25% of field capacity) on the growth and biochemical characteristics of the yew plant in a greenhouse environment in three replications in the form of a completely randomized design. in this research, which used 3-year-old seedlings, the fresh-to-dry weight ratio of shoots and roots, chlorophyll a and b and the ratio of these two, the relative content of leaf water, the activity of superoxide dismutase and catalase enzymes, and the percentage and yield of essential oil were evaluated. the results showed that the growth traits and photosynthetic pigments and the relative water content of the leaves decreased with the increase in the severity of drought stress. of course, the activity of catalase and superoxide dismutase enzymes increased with the intensity of drought stress. the highest percentage of essential oil was obtained in semi-severe drought stress conditions (50% f.c). with the increase of drought stress up to 25% f.c, the percentage of essential oil decreased. most of the growth and physiology parameters of yew plant at 75% fc compared to 100% fc were not significantly different, so it seems that this plant shows good tolerance in the condition of 75% fc and has an acceptable yield. therefore, it is recommended to cultivate this valuable plant in favorable environmental conditions with sufficient water and/or with only in mild stress conditions.