Leaf photosynthesis and carbon isotope discrimination of cotton in response to potassium deficiency

Abstract

Leaf photosynthesis and stable carbon isotope composition in response to potassium (K) deficiency was determined with cotton. Cotton plants were grown in sand-filled 8-l pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, Arkansas. Plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting (the fourth true leaf stage) the treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Leaf photosynthesis and related gas exchange measurements were taken 13, 19, and 26 days later. Leaf samples from each analysis date were then dried and reserved for nutrient and carbon isotope analyses. Photosynthesis declined as the K deficiency developed in the no-K treatment. Decreased ∂ A/∂ c i and increased Γ also resulted from declined leaf K concentration, which is attributed to changes in A and respiration in the light. Potassium deficiency also resulted in increased stomatal and non-stomatal limitations to A. Gas exchange studies showed stomatal conductance was most limiting to A at 13 days after treatment establishment (DATE), whereas instantaneous measurements at 19 and 26 DATE indicated non-stomatal conductances were most limiting. However, carbon isotope analyses, which integrated stomatal and non-stomatal conductances over the entire analysis period, indicated that the most limiting resistance to A was stomatal. We conclude from these studies that, during a mild K deficiency, increased stomatal resistance is first to result in a decrease in A and, as the deficiency becomes more acute, biochemical factors also contribute.