Impact of Irrigation Cessation on Physiological, Photosynthetic, and Enzymatic Activities in Wheat (Triticum aestivum L.) at Varying Plant Densities

Drought stress is one of the most critical factors reducing the performance of crop plants in arid and semi-arid regions globally, highlighting the importance of understanding underlying mechanisms to combat such stress. Therefore, this experiment aimed to investigate the effect of drought stress and planting density on the physiological characteristics, photosynthetic pigments, and enzymatic activity of wheat plants. The experiment was conducted in a factorial arrangement based on a completely randomized block design with three replications. The treatments included irrigation cessation at three levels (control, irrigation until flowering (IUF), and irrigation until the roughing (IUD)), and plant density (300, 400, 500, and 600 plants m-2). The results indicated that leaf relative water content, soluble sugars, cell membrane stability index, chlorophyll a, b, and carotenoids were significantly decreased at IUF treatment, while these parameters increased at higher plant densities. Additionally, the interaction of drought stress and plant density significantly affected leaf proline and flavonoid content, total chlorophyll, and catalase activity. The highest leaf proline content (3.88 mg g-1 FW) was observed in the treatment with IUF and a density of 600 plants m-2, representing a 192% increase compared to the control. Additionally, the highest total chlorophyll content (3.66 mg g-1 FW) was recorded at no-stress conditions with a density of 500 plants m-2. Under drought stress conditions, the activity of antioxidant enzymes also increased. Overall, our results indicate that a density of 500 plants m-2 is optimal for maintaining stable growth conditions in wheat. These findings provide valuable insights for policymakers to develop effective agronomic strategies to mitigate drought stress, particularly in arid and semi-arid regions.