Effect of high night temperatures on cotton respiration, ATP levels and carbohydrate content

High night temperatures are considered to be one of the main environmental factors contributing to lowered yields in cotton and this has been attributed to a negative effect on respiration and carbohydrate accumulation, but the evidence for this is lacking. Studies were conducted to determine the effect of high night temperatures on cotton respiration, adenosine 5′-triphosphate (ATP) levels and carbohydrates content. Two sets of growth chamber studies were conducted in 2007 using cotton (Gossypium hirsutum L.) cultivar DP444BG/RR. The first set focused on the short-term effect (2 h) of high night temperatures, with plants grown under normal day/night temperatures of 30/20 °C until the pinhead square stage, after which temperatures of 24, 27 and 30 °C were imposed for one night with 2-h intervals between each incremental temperature regime. The results showed that both high temperature regimes (27 and 30 °C) caused a significant increase in respiration rates by 49% and 56%, respectively, compared to those of the control (24 °C). ATP levels were significantly decreased proportionally to the increasing temperature regimes while the carbohydrate content remained unaffected. The second set of experiments, dealt with the effect of long-term (four weeks) high night temperatures, with treatments consisting of normal 30/20 °C (day/night) temperatures and high night temperatures (30/28 °C) for four weeks, again after the pinhead square stage. A significant increase in respiration was observed the second and the fourth week (39% and 21%, respectively) and a decrease in ATP levels (by 38% and 37%, respectively) of the plants in the high night temperature regime. Similarly, high night temperatures led to a consistent decrease of sucrose by 64%, 70% and 68%, and hexose by 33%, 28% and 39% for the weeks one, two and four, respectively. In general, high night temperatures increased respiration, which resulted in a reduction of leaf ATP levels and leaf carbohydrate content.