Temperature is a Primary environmental factor controlling the rates of several plant processes. Cotton (Gossypium hirsutum L.) plants were grown in a nearly natural environment with temperature as a variable controlled during the fruiting period. Plants were grown outdoors in pots and moved into sunlit temperature controlled growth chambers five days prior to initial bloom. Plant growth and development were measured under 20/10, 25/15, 30/20, 35/25, and 40/30 C day/night temperature regimes from initial bloom for 50 days.

Temperature significantly affected biomass production and partitioning of assimilates to different plant parts. Optimum temperature for biomass production was 30/20 C. Compared to the 30/20 C treatment, biomass accumulation decreased up to 40% and 50% at lower (20/10 C), and higher (40/30 C) temperatures respectively. Plants grown at the optimum temperature (30/20 C) partitioned nearly 43% of their total biomass to reproductive structures compared to 13% at 20/10 C and 15% at 25/15 C treatment. At the higher temperatures, biomass partitioned to reproductive structures was negligible compared to vegetative structures.

Growth rates of different plant parts reflected similar responses due to temperature. The growth of the main stem at 30/20 C was more rapid initially, but further growth was restricted due to the formation of bolls which competed for the available carbohydrates. The growth of successive main-stem leaves was affected similarly to that of main-stem growth at the various temperatures. Specific leaf area (SLA) of all the leaves increased as temperature increased up to 30/20 C and then declined slightly. The SLA of vegetative branch leaves; however, increased up to 35/25 C and then declined at 40/30 C. The change in SLA of leaves initiated after temperature treatment was more dramatic than in existing leaves. Decreased SLA of main-stem and branch leaves at higher and lower temperatures than optimum (30/20 C) may reflect temperature effects on the development of bolls and partitioning of assimilates into reproductive growth.