ABSTRACT
The unpredictability of cotton yields is a great concern to cotton industry. The five-year average yield for cotton in the U.S.A. is 718lb lint/acre, whereas the theoretical maximum lint yield is 3720 lb lint/acre. High temperatures are considered to be one of the main environmental factors contributing to variable yields in cotton. This is apparently due to a negative effect on respiration and carbohydrate accumulation but the evidence for this is lacking.  Yield comparisons between areas with same day temperatures and different night temperatures have shown that the areas with higher night temperatures have lower yields.  In this study it was hypothesized that high night temperatures have a negative effect on cotton photosynthesis and respiration that results in a significant loss of carbohydrates and ultimately in a yield decrease. Four growth chamber studies were conducted in 2007, at the Altheimer Laboratory, University of Arkansas. Treatments were comprised of normal and elevated night temperature regimes, and measurements were made of photosynthesis, respiration and carbohydrates status. The results are currently being analyzed.