Potassium and Phosphorus

Abstract

The solute concentrations contributing to the leaf osmotic potentials of sunflower plants (Helianthus annuus L., cv. Zwerg Sonnengold) were investigated at varied potassium and water supplies. Plants were grown in pots containing 12 kg of soil fertilized with 0.6 g (K₁) and 5.0 g K/pot (K₂). At the age of 35 days, 50% of the plants were well‐watered (controls) and 50% were subjected to water stress. After severe wilting, the stressed plants were re‐watered. The effect of water stress on solute concentrations was not pronounced, so that their increase under drought conditions is assumed to be mainly due to tissue water loss rather than to active accumulation processes. In contrast, the distinct differences in potassium supply resulted in significant changes in the solute composition. K⁺ concentrations ranged between 129 and 194 meq/l cell sap in K2 plants (K₁: 16–60 meq/l). In K deficient plants K⁺ was replaced by Mg²⁺ and Ca²⁺. K₁ plants accumulated higher amounts of sugars (mainly glucose and fructose). The total amount of organic acids was higher in K₁ plants. The dominant organic anion was citrate in K₁ plants and fumarate in K₂ plants.

Key words:

• Helianthus annuus L.
• potassium nutrition
• water stress
• cations
• organic acids
• carbohydrates