Influence of Potassium Stress on Growth, Stomatal Behavior, and CO2 Assimilation in Corn 1

Crop potassium stress could be more easily diagnosed if the sequential plant responses to K deficiency were known. A greenhouse study was conducted to determine plant responses to K stress at several stages of development of corn ( Zea mays L.). Potassium was supplied at 0.50 m M (Kl) and 3.0 m M (K2) of nutrient solution. Leaf stomatal resistance (r s ) and CO 2 uptake of the youngest fully expanded intact leaves were measured 30, 47, and 62 days after emergence. Potassium concentration of individual leaves of K‐adequate (K2) plants declined progressively with maturity; however, leaves of K‐stressed (Kl) plants declined to a much greater extent. High t, was associated with low K concentration of leaves at all three measurement dates. Stomatal frequency did not vary significantly with K treatment. The increase in r s did not result in reduced CO 2 assimilation rates or plant dry matter weights at 30 or 47 days. At 62 days, r6 for leaves of K‐stressed plants was nearly 30% higher than for K‐adequate plants. Leaf area/plant was not significantly different; however, CO 2 uptake was nearly 70% lower for K‐stressed plants at 62 days. There was a corresponding 30% reduction in dry matter accumulation for K‐stressed plants. High leaf K levels were associated with high specific leaf weights (SLW). Both high rs and low SLW in low‐K plants occurred before visible K deficiency was evident and at a concentration above the reported critical concentration. Potassium deficiency symptoms were not evident at any time during the experiment on recently expanded leaves of Kstressed plants. Increased r s and decreased SLW were early indicators of developing K stress and may be useful in diagnosis of K deficiency