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Influence of Potassium Stress on Growth, Stomatal Behavior, and CO₂ Assimilation in Corn1¹

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 (r_s) 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 r_s 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 r_s and decreased SLW were early indicators of developing K stress and may be useful in diagnosis of K deficiency

Key Words: K nutrition • Zea mays L. • Stomatal resistance • Stomatal frequency • Specific leaf weight • photosynthesis

² Assistant professor and associate professor, Dep. of Plant Sci., Univ. of N.H., Durham, NH 03824.

Received for publication November 19, 1974.