Potassium deficiency impedes elevated carbon dioxide-induced biomass enhancement in well-watered or drought-stressed bread wheat

Potassium (K) deficiency reduces photosynthesis and biomass production of crop plants and also renders them vulnerable to drought stress, whereas elevated carbon dioxide (CO2) has a positive effect on photosynthesis and yield and ameliorates the adverse effects of drought stress. This study aimed to characterize the physiological responses of wheat (Triticum aestivum L.) stressed with K deficiency under elevated CO2 and drought conditions. Increased biomass production caused by elevated CO2 as a consequence of increased photosynthesis and water use efficiency was absent in young K-deficient wheat plants. Shoot K concentration was negatively affected by elevated CO2 particularly under K-deficient conditions, whereas K content per plant was greatest in plants supplied with adequate K and adequate water. Specific leaf weight was increased as a consequence of carbohydrate accumulation in the source leaves of K-deficient plants particularly under elevated CO2 and drought stress. Potassium deficiency clearly impeded the impact of elevated CO2 in both well watered as well as drought-stressed plants. Adequate K fertilization is a prerequisite for efficient harvesting of atmospheric CO2 through increased photosynthesis, decreased transpiration, and increased biomass production under changing atmospheric CO2 and soil moisture conditions.