Study of morphological and physiological response of red root pigweed (Amaranthus retroflexus L.) to drought stress

Redroot pigweed (Amaranthus retroflexus L.) is a noxious and cosmopolitan weed that is widely distributed in different parts of the world and competes severely with crops and reduces their growth and yield. The present study was conducted to investigate the effect of drought stress on some morphological and physiological characteristics of redroot pigweed in 2018 and 2019. Treatments included different degrees of drought stress with 5 levels including 100, 75, 50, 25, and 12.5% ​​of pot water content (equivalent to no stress, light stress, moderate stress, high stress, and severe stress). Leaf number, plant height, and leaf dry weight were affected by the interaction of drought stress×years and with increasing drought stress, leaf number, plant height, and leaf dry weight decreased in both years of the experiment. With decreasing the water content of the pot, the activity of catalase and superoxide dismutase increased. The highest levels of catalase and superoxide dismutase activity (110.35 and 1433.33 units of enzyme/mg protein per minute) were observed in the second year under severe stress, respectively. Increasing the intensity of stress decreased the soluble protein content of the plant. Also, drought stress reduced plant chlorophylls a and b content, whereas, carotenoid content increased. The highest amount of carotenoids was observed in both years under severe drought stress conditions. Overall, drought stress in the second year reduced growth in redroot pigweed further but in this year, the enzyme activity ramped up further. Therefore, this plant can modify stresses and maintain its survival by changing its biochemical activity.