THE INFLUENCE OF CONSTANT AND DIURNALLY CHANGING CO2 CONCENTRATIONS ON PLANT-GROWTH AND DEVELOPMENT

Plants of Ficus benjamina and miniature rose (Rosa hybrida cv. Red Minimo) were grown under four CO2 treatments. Two had constant CO2 levels (600 and 900 ppm) and the other two had diurnal changes in CO2 levels, one increasing from 600 to 1500 ppm and one decreasing from 1500 to 600 ppm, each in four steps of 300 ppm during the day-time. In all treatments 900 ppm CO2 was maintained during the night when supplementary light was used, except in the treatment with constant 600 ppm where 600 ppm was also continued throughout the night. Plant growth was monitored under both decreasing and increasing natural daylength and irradiance. The tallest plants and greatest increment in height for Ficus occurred with plants grown under constant CO2 concentration at 600 ppm and also with increasing CO2 concentration. In both experiments the dry weight per pot was lowest when plants were grown under a constant CO2 concentration at 900 ppm. In both experiments with miniature roses the number of flower buds was significantly increased under diurnally changing CO2 concentration or when the CO2 level was constant at 600 ppm compared with a constant 900 ppm. Time to flowering was decreased by constant CO2 at 900 ppm as compared with the other treatments.