Influence of Potassium Stress on Growth, Stomatal Behavior, and CO2 Assimilation in Corn1

Abstract

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 mM (Kl) and 3.0 mM (K2) of nutrient solution. Leaf stomatal resistance (rs) and CO2 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 rs did not result in reduced CO2 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, CO2 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 rs and decreased SLW were early indicators of developing K stress and may be useful in diagnosis of K deficiency