RESPIRATION AND GROWTH OF SORGHUM AND SUNFLOWER UNDER PREDICTED INCREASED NIGHT TEMPERATURES

Little information exists concerning how crops will respond to the pre dicted increased night temperatures. The objective of this work was to determine if respiration and growth of sorghum [Sorghum bicolor (L.) Moench], a C-4 plant, and sunflower (Helianthus annuus L.), a C-3 plan t, are affected when the night temperature is increased by 5 degrees C compared to the long-term (19 year) average night temperature in June in Kansas. Sorghum and sunflower were grown in two walk-in growth cha mbers with either the ambient night temperature (21 C) or a high night temperature (26 C). Day temperature was the same for all plants (27 C ). Both sunflower and sorghum had higher respiration rates under the e levated night temperature than under the ambient temperature. The aver age respiration rate of sunflower grown under elevated night temperatu re increased by 19 % (0.89 vs. 0.75 mu mol m(-2) s(-1)) and that of so rghum by 44 % (0.52 vs. 0.36 mu mol m(-2) s(-1)). After 74 days, sunfl ower plants grown under the ambient night temperature were 30.2 cm tal ler than sunflower plants grown under the elevated night temperature; sorghum plants under the ambient temperature were 24.8 cm taller. Sunf lower plants grown under the elevated night temperature formed flowers one week earlier than those grown under the ambient temperature. Sorg hum formed no flowers by 74 days. Results suggest that, if climate cha nge does increase night temperature, respiration will be increased mor e in C-4 than C-3 plants.