Promotive Effect of CO2 Enrichment on Plant Growth and Flowering of Eustoma grandiflorum (Raf.) Shinn. under a Winter Culture Regime

Cut Eustoma grandiflorum (Raf.) Shinn. flowers are produced year-round in Japan; however, winter conditions are not favorable for flower production due to low sunlight levels. Here, we investigated the effect of CO2 enrichment after the flower budding stage on the growth and flowering of Eustoma ‘Bolero White’, which were grown under forcing culture for winter shipping. CO2 enrichment increased the fresh weight of plants, in addition to increasing the dry weights of leaves, stems, flower buds and open flowers, and roots. CO2 enrichment also increased the relative growth rate (RGR) by 32%, due to the net assimilation rate (NAR) being stimulated. However, CO2 enrichment had no effect on plant height or the leaf area ratio (LAR). Furthermore, CO2 enrichment increased the total number of flower buds and open flowers, in addition to accelerating flower bud development and the promotion of flowering. During the period of enrichment, the vegetative organs continued to grow in CO2-enriched plants, but not in the control plants. In conclusion, CO2 enrichment promoted flowering and improved the quality of cut flowers (i.e., increasing plant fresh and dry weight and the total number of flower buds and open flowers) of Eustoma under low-sunlight winter conditions.