Effects of High Night Temperatures on Cotton Leaf Gas Exchange and ATP Levels at Flowering

Aims: To monitor the effects of high night temperatures on leaf photosynthesis and respiration, stomatal conductance and adenosine triphosphate (ATP) levels of cotton during its reproductive stage.
Study Design: A two-factor factorial, the two factors being temperature and time (weeks), with 40 replications in each of the temperature treatment.
Place and Duration of Study: Altheimer Laboratory, Department of Crop, Soil and Environmental Sciences, University of Arkansas, between September 2013 and June 2014.
Methodology: Growth chamber experiments were conducted using cotton (Gossypium hisrsutum L.) cultivar ST5288B2F with the treatments consisting of normal day/night temperatures (32/24ºC) and high night temperatures (32/30ºC) for two weeks at flowering. Measurements of leaf photosynthesis, respiration, stomatal conductance and ATP levels were conducted in the end of the first and the second week after imposition of stress.
Results: Leaf photosynthetic rates and stomatal conductance rates remained unaltered under higher night temperatures during both weeks of the experiment. In contrast, a significant increase in leaf respiration rates was observed at the end of the second week of the experiment with plants grown under conditions of high night temperatures increasing their respiration rates by 30% compared to those grown under normal temperatures. Conversely, leaf ATP levels were significantly decreased under conditions of elevated night temperatures.
Conclusion: It was concluded that higher than optimum temperatures during flowering had no significant effect on cotton leaf photosynthesis and stomatal conductance in contrast to leaf respiration and ATP levels that were significantly decreased.