Physiological characterisation of two rose (Rosa hybrida L.) cultivars grown under different levels of CO2 enrichment

The rose cultivars 'Arjun' (indigenous) and 'First Red' (exotic) were grown in a phytotron and exposed to 370 (ambient), 1,000, or 1,500 mu mol mol(-1) CO2 to Study their physiological response in relation to CO2 enrichment. 'Arjun', grown under 1,000 mu mol mol(-1) CO2 achieved a maximum height of 95.0 cm, compared to 83.3 cm under ambient CO2. The total number of leaves and leaf area were highest at 1,500 mu mol mol(-1) CO2 in both cultivars. Photosynthesis, chlorophyll concentration, and specific leaf weight (SLW) were measured at the flowering stage. Maximum photosynthetic rates were achieved at 1,000 mu mol mol(-1) CO2 (11.59 and 10.42 mu mol CO2 m(-2) s(-1) in 'Arjun' and 'First Red', respectively), compared to 3.66 and 4.96 mu mol m(-2) s(-1), respectively at ambient CO2 levels. Chlorophyll a. ch1 b, and total chlorophyll concentrations in leaves increased in both cultivars at 1,500 mu mol mol(-1) CO2, while chi a/b ratios decreased due to CO2 enrichment. SLW was higher in both cultivars at 1,000 mu mol mol(-1) CO2 compared to ambient CO2. Root dry weight was significantly higher at 1,000 mu mol mol(-1)' CO2 in both cultivars than at ambient CO2, whereas root volume was maximum (28.2 cm(3)/plant) in 'First Red' at 1,500 mu mol mol(-1) CO2 compared to 'Arjun' (23.3 cm(3)/plant). Cultivar X CO2 interactions were also significant for all parameters measured. The indigenous rose cultivar 'Arjun' responded positively in terms of growth and photosynthetic rate to CO2 enrichment under optimum growing conditions. Physiological characterisation can thus provide useful information to select rose cultivars to be grown under modified environments to achieve their maximum yield potential.