Respiration of geranium and petunia in response to low night temperature

Abstract

The morphology and rate of development of some bedding plant species is altered by growth at low night temperatures. This cultural practice is of interest because it results in lower greenhouse energy costs and higher productivity at low photosynthetic photon flux. Low night temperatures and changes in the carbohydrate content of the plants may alter energy losses from maintenance respiration. To test this hypothesis, seedlings of geranium (cultivar ‘Red Elite’) and petunia (cultivar ‘Snow Cloud’) were grown at day temperatures of 25°C and night temperatures of either 7°C or 15.5°C. Thereafter, CO 2 evolution in the dark at 21°C was measured and starch, soluble sugar and total nitrogen levels were determined. The respiration rates at 21°C of plants grown at 7°C night temperature were consistently higher than those of plants grown at 15.5°C night temperature. Plants grown at the low night temperature had higher starch and soluble sugar levels, even after 112 h in darkness. Effects of night temperature in winter on maintenance respiration and reserve carbohydrate accumulation are discussed.