Influence of temperature on net CO₂ exchange in roses

Abstract

The effect of temperature on net CO 2 exchange of source and sink tissues of the flowering shoots and of whole plants was examined using single-stemmed Samantha roses. At all stages of shoot development, the optimal temperature range for whole-plant carbon (C) gain at saturating irradiance and ambient CO 2 level was between 20° and 25 °C, narrower than the temperature range for optimal leaf net photosynthesis. Dark respiration increased more dramatically than photosynthesis with temperatures between 15 and 35 °C. At 25 °C, C loss due to respiration from the flower bud at colour bud stage accounted for 45% of the C loss of the flowering shoot. At low irradiance levels (e.g. 200 μmol m −2 s −1 ) whole-plant net photosynthesis was greater at 16° than at 22 °C because of a greater reduction in respiration. Lowering the night temperature from 27 to 17 °C also increased daily C gain due to a reduction in the C lost at night. Whole-plant net photosynthesis of plants grown and measured at enriched (1000 ± 100 μL L −1 ) CO 2 was greater than that of plants grown and measured at ambient (350 ± 50 μL L −1 ) level at temperatures between 15° and 35 °C. Furthermore, the optimal temperatures for whole-plant net photosynthesis in CO 2 enrichment was higher than at ambient CO 2 level. Key words: Dark respiration, net photosynthesis, Rosa hybrida, temperature