Investigation of the drought stress on some photosynthetic and morphological indicators of summer savory (Satureja hortensis L.)

In order to better management of plant performance under conditions of drought stress and study of the condition of plant growth, transpiration, plant stomatal conductance, plant photosynthesis (main determinant of plant growth), photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoid), a completely randomized block design with three replications was conducted in the Faculty of Agriculture of Lorestan University in 2017. The water stress treatments including 100, 80, 60 and 40 Percent of water requirement were applied. Irrigation was performed based on weighing method. Gas exchange measurements and morphological harvesting were done 80 and 90 days after stress. Results showed that water stress treatment has a significant reduction of stomatal conductance, transpiration rate, photosynthesis rate, intercellular CO2 concentration, photosynthetic water use efficiency and carboxylation efficiency. The highest values of the above parameters were related to control treatment and the lowest values were observed in treatment of 40% of water requirement. these values were decreased 68.08%, 59.99%, 61.42%, 37.96%, 20.79% and 37.5%, respectively, compared to the control treatment. As the result showed, the amount of stomatal conductance, transpiration rate, photosynthesis rate are affected by drought stress more than other parameters. Photosynthetic pigments were decreased significantly by increasing drought stress. The highest and lowest of chlorophyll a and b and carotenoid observed in control and heavy drought stress. Finally, drought stress significantly reduced the growth parameters such as plant height, stem diameter, dry weight of the plant.