مطالعه اثرات تنش شوری بر عملکرد و شاخص‌های فیزیولوژیک گندم در شرایط مزرعه

Wheat, as one of the most strategic crops, plays a vital role in ensuring food security for the world's growing population. However, the production of this valuable crop always faces several challenges, including abiotic stresses. In the meantime, soil and water salinity, as a widespread problem, is considered a serious threat to wheat cultivation, especially in arid and semi-arid regions such as Iran. Salinity stress disrupts the physiological and biochemical processes of the plant through the reduction of soil water potential (osmotic effect) and the accumulation of toxic ions such as sodium and chlorine (ionic toxicity), and ultimately leads to a severe decrease in grain yield. Investigating the effect of different levels of irrigation water salinity on physiological traits (chlorophyll, proline content, and electrolyte leakage), yield components (number of grains per spike and thousand-grain weight), and final grain yield of wheat cultivar Chamran 2 under real field conditions in the semi-arid climate of Ilam.
Materials and Methods
This field study was conducted in the 1402-1403 crop year in Ilam (46°26′E longitude, 33°38′N latitude, 1174 m altitude) with a semi-arid climate (Dumartin). The experiment was conducted in a randomized complete block design with four irrigation water salinity treatments (control 2, 4, 6, and 8 dS/m) and three replications. Wheat seeds of the Chamran 2 variety were sown at a density of 400 seeds/m2 in 3×4 m plots (16 rows with 25 cm spacing). Salinity stress was applied from the 3-4 leaf stage to full maturity, and 15% leaching was considered to prevent salt accumulation. Flag leaf sampling was performed at the pollination stage and total chlorophyll (80% acetone and spectrophotometry), proline (ninhydrin method), and electrolyte leakage were measured. Yield and its components were harvested from a 2 m2 area. Data were analyzed with SAS software and means were compared using Duncan's test (5%).
Results
The results of this study clearly show that salinity stress in irrigation water has a profound and significant effect on all morphological, functional and physiological traits of wheat. The appropriate uniformity of the field bed (no significant block effect) and high precision of the experiment (CV less than 10%) confirm the validity of the data. Increasing the electrical conductivity of water from 2 to 8 dS/m reduced grain yield by 42% (from 6250 to 3610 kg/ha), which was due to a simultaneous decrease in thousand-grain weight (43%) and number of grains per spike (35%). At the physiological level, total chlorophyll content decreased by 58% to 1.60 mg/g fresh weight, indicating severe destruction of chloroplasts. In contrast, proline, as a defense mechanism, increased 4-fold (from 2.4 to 16.5 μmol/g) and electrolyte leakage, indicating membrane damage, increased from 18.5 to 52.6%. The strong correlation between yield and chlorophyll (0.92) and electrolyte leakage (-0.94) confirms that cell membrane damage and reduced photosynthetic capacity are the main mechanisms of yield reduction under salinity conditions. In general, wheat plants at salinity levels above 6 dS/m face severe yield reduction and irreversible physiological disorders.
Overall Conclusion
Salinity stress, by affecting key physiological processes including chloroplast destruction (58% reduction in chlorophyll), increased electrolyte leakage and proline accumulation, significantly reduces yield components and ultimately wheat grain yield. The strong correlation between traits suggests that physiological indices such as chlorophyll and electrolyte leakage can be used as reliable criteria for screening salt-tolerant cultivars. Considering the 42% yield reduction at 8 dS/m salinity, water resource management and the use of salt-tolerant cultivars are essential for cultivation in arid and semi-arid regions.