Effect of Potassium Optimization on Wheat Drought Tolerance in Controlled Conditions

Wheat (Triticum spp.) is an important cereal crop consumed worldwide, but it is highly susceptible to drought. Potassium plays an essential role in osmotic regulation, photosynthesis, and nitrogen assimilation, all of which are critical for maintaining plant growth and productivity under stress conditions. The aim of this study is to investigate how different potassium levels, including sufficient potassium (SK, 1 mM) and low potassium (LK, 0.05 mM), affect the drought tolerance of wheat during the early stages of seedling development under PEG-induced drought stress. Plant physiological development, canopy temperature, photosynthetic efficiency, antioxidant defense enzymes, and nitrogen assimilation enzymes were assessed in the experiment. In non-drought conditions, LK increased canopy temperature and reduced dry matter yield and photosynthetic performance, with these effects becoming more pronounced under drought stress. SK-treated plants exhibited higher biomass, chlorophyll content, maximum quantum efficiency of photosystem II, and lower canopy temperatures, even under drought conditions. Furthermore, LK restricted the accumulation of key osmotic regulators, including proline, amino acids, and soluble sugars. Under drought stress, LK plants also showed increased hydrogen peroxide and superoxide anion levels, while SK plants had lower reactive oxygen species accumulation and higher antioxidant enzyme activities (catalase and superoxide dismutase). Additionally, LK resulted in reduced activity of nitrogen assimilation enzymes (nitrate reductase, NR, and nitrite reductase, NiR) under both normal and drought conditions. In contrast, SK-treated wheat seedlings maintained higher NR and NiR activities and higher soluble protein content during drought stress. These findings underscore the critical role of potassium management in enhancing wheat yield, particularly in water-scarce regions, as optimal potassium supply strengthens essential physiological and biochemical mechanisms that improve plant tolerance to drought stress.