Water Status and Leaf Area Production in Water‐ and Nitrogen‐Stressed Cotton

Abstract

The combined effects of water and N deficits on leaf area production and water relations in cotton (Gossypium hirsutum L.) have not been investigated thoroughly. A study was conducted to evaluate the responses of leaf area production and water relations in cotton plants exposed to water and N deficits during the preflowering stage. Two N treatments‐nutrient solution with 12 mM of N (N‐supplied) and N‐free nutrient solution (N‐starved)‐were applied to plants when the third true leaf was visible. Two irrigation treatments‐daily irrigation (well watered) and no irrigation (water stressed)‐were superimposed on each N treatment once the plants were moved into the test chambers when they reached a leaf area of 0.050 ± 0.002 m2. Leaf area and leaf water and osmotic potentials were measured at the end of each day‐time period. Under well‐watered conditions, leaf turgor potential in N‐starved plants was about 0.3 kJ kg−1 lower than in N‐supplied plants. When plants were exposed to water deficits, the decline of leaf water potential relative to soil water content was greater in N‐starved plants than in N‐supplied plants. Nitrogen deficiency delayed and decreased the magnitude of osmotic potential adjustment and, therefore, reduced the capacity of leaves to maintain turgor. Water and N deficits decreased whole‐plant cumulative leaf area about 50 and 40%, respectively, through decreased daily production of mainstem and branch leaves and decreased final area of individual mainstem and branch leaves. Nitrogen deficiency induced a higher sensitivity of leaf growth inhibition to water deficits.