Temperature Effects on Cotton Canopy Growth, Photosynthesis, and Respiration

The ecological range of temperature conditions where cotton ( Gossypium hirsutum L.) is commercially grown frequently exceeds the temperature range of available data. To predict growth, development, and responses of the primary physiological processes to those conditions, data at both lower and higher temperatures are needed. Cotton plants were grown in naturally lit, temperature‐ and CO 2− controlled chambers. Plants grown at near‐optimum temperatures (30 and 35 °C day temperature) fixed twice as much CO 2 at high photosynthetically active radiation during the fruiting period as did plants growing at 20 °C. Growth exhibited similar differences due to temperature during the boll‐filling period. Plants with heavy fruiting load partitioned less to vegetative structures. Most plants grown at 35/25 °C day/night temperatures and all those grown at 40/30 °C had serious flower survival problems. No fruits were harvested from the plants grown in the 40/30 °C chamber and only a few from those grown in the 35/25 °C chamber. Gross photosynthesis, canopy light utilization efficiency, and canopy conductance were found to be highly variable from day to day. This variability should be considered by investigators measuring short‐term CO 2 exchange rates. Respiration rates of cotton plants were 45% higher during the first hour of dark than during the rest of the night. These data suggest that carbohydrate is more readily available for respiration during and immediately after the light period than later in the dark period.