Influence of radiation and CO 2 enrichment on whole plant net CO 2 exchange in roses

Abstract

At three stages of flowering shoot development, varying the irradiance and CO 2 levels had a similar effect on the whole-plant net CO 2 exchange rate (NCER) of Samantha rose plants. At 22 °C, the NCER was saturated at 1000 μmol m −2 s −1 photosynthetically active radiation (PAR). The duration of the light period was also important in determining daily carbon (C) gain. When roses were exposed to a constant daily radiant energy dose of 17.6 μmol m −2 provided either as a 12-h irradiation interval at 410 μmol m −2 s −1 PAR or 24 h of irradiation at 204 μmol m −2 s −1 PAR, the plants exposed to 24 h of continuous irradiation at the lower photon flux density retained 80% more C. Under saturating irradiance, the net photosynthetic rate at an enriched (1000 μL L −1 ) CO 2 level was almost double that at ambient (350 μL L −1 ) CO 2 . However, plants grown at ambient and enriched CO 2 levels had similar whole-plant NCERs when compared at the same assay CO 2 level. Under CO 2 enrichment the flower stem was longer and thicker but the flower bud size at harvest was not significantly different to that of roses grown at the ambient CO 2 level. Key words: CO 2 enrichment, daily carbon gain, net CO 2 exchange rate, radiation, Rosa hybrida