Water status and leaf area production in water- and nitrogen-stressed cotton
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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.