Drought effects on growth, biochemical changes and leaf gas exchange in laurel (Laurus nobilis L.)

Drought is one of the abiotic factors that negatively affect the productivity of laurel (Laurus nobilis L.). Increasing water scarcity in arid and semi-arid regions is pushing the physiological limits of woody species, necessitating strong resistance to drought. Studies should be conducted on the effects of drought stress not only on forest trees but also some medicinal and ornamental species, and ways to increase their resistance should be explored. This study was carried out to determine the effect of drought stress on seedling growth and some physiological and biochemical properties in laurel. The seedlings were subjected to drought stress for about 4 months with three different irrigation regimes: watering once every 2–3 days (control), every 15 days, and every 30 days. Morphological properties (root collar diameter, height, dry weight, stem: root ratio, and number of leaves), physiological properties (midday xylem water potential and photosynthesis properties), and biochemical properties (photosynthetic pigments, total carbohydrate, and proline contents) were determined. Results have shown that drought stress has a negative effect on root collar diameter, seedling height, and dry weight. Likewise, leaf number and midday xylem water potential decreased due to increased drought stress. Furthermore, the net photosynthesis rate, stomatal conductance, and transpiration rate of the least irrigated (30^th day) seedlings were quite low compared to those of control seedlings. The differences in chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents were also found to be statistically significant. Total carbohydrate and proline contents showed the highest values for the least irrigated seedlings and the lowest values for controlled irrigation seedlings. Our results reflect the improved tolerance capacity of laurel to increased drought stress.