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 (CO 2 ) 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 CO 2 and drought conditions. Increased biomass production caused by elevated CO 2 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 CO 2 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 CO 2 and drought stress. Potassium deficiency clearly impeded the impact of elevated CO 2 in both well watered as well as drought‐stressed plants. Adequate K fertilization is a prerequisite for efficient harvesting of atmospheric CO 2 through increased photosynthesis, decreased transpiration, and increased biomass production under changing atmospheric CO 2 and soil moisture conditions.