Flowering and Photosynthetic Responses of Phalaenopsis under Elevated CO2 and Nutrient Supply

The demand for phalaenopsis has been increasing in areas including Thailand, Japan, and the United States.Increasing atmospheric CO2 during the night improves the productivity and quality of phalaenopsis flowers.Because nutrient requirements change under conditions of elevated CO2, the interactive effects of CO 2 enrichment and nutrient supply require particular attention.Our study aimed to discover the effect of nutrient treatments on phalaenopsis using electrical conductivity (EC) when applying CO2 in the greenhouse.We investigated the flowering and photosynthetic responses of Phalaenopsis Queen Beer 'Mantefon' and 'Jupiter' in response to EC-based nutrients supplied with 1.0 (control) and 2.0 dS•m -1 and two levels of ambient and elevated CO2 (≈ 650 µmol•mol -1 CO2) for a period of 21 weeks of treatment (WOT).A longer first flower spike was produced in the plants exposed to EC 2.0 dS•m -1 than in those exposed to EC 1.0 dS•m -1 under elevated CO2, regardless of the phalaenopsis cultivar.Responses to CO2 and EC in the second flower spike length varied among phalaenopsis cultivars during 0 to 18 WOT; however, maximum second spike length was obtained with EC 2.0 dS•m -1 under elevated CO 2 at 21 WOT in 'Jupiter'.More visible flower buds and lateral branches were observed in plants exposed to EC 2.0 dS•m -1 under elevated CO2.The net CO2 assimilation rate showed significance with CO2 treatment, regardless of phalaenopsis cultivar.The most flowers were produced in the plants exposed to EC 2.0 dS•m -1 under ambient CO2 in both phalaenopsis cultivars, but water use efficiency, as well as potential yield, were the highest in plants exposed to EC 2.0 dS•m -1 under elevated CO2.We conclude that ≈ 650 µmol•mol -1 CO 2 increased the flowering quality of phalaenopsis and recommend adjusting the nutrient concentration with an EC of 2.0 dS•m -1.