LAUSR

Abstract Obligate crassulacean acid metabolism (CAM) plants rely heavily on nocturnal CO2 fixation; however, little is known about how changes in CO2 concentration affect the nutrient requirements of these plants. To evaluate the combined effect of CO2 concentration and nutrient provision on obligate CAM plants, we cultivated Phalaenopsis Queen Beer ‘Mantefon’ under two CO2 concentrations (400 or 800 μmol· mol−1) and with four nutrient solutions (EC [electrical conductivity] of 1.0, 2.0, 3.0, or 4.0 dS·m−1) for 17 weeks. Various flowering characteristics of Phalaenopsis (flower spike length, the number of lateral branches, floral buds, and flowers, days to flowering, flower size, and flower color) were then investigated during the reproductive stage. Overall, higher CO2 concentrations enhanced the growth and productivity of Phalaenopsis. More specifically, flower spike lengths were longer and more lateral branches were initiated under 800 μmol·mol−1 CO2 compared to plants cultivated under 400 μmol·mol−1 CO2 with an EC of 3.0 or 4.0 dS·m−1. Additionally, plants cultivated under 800 μmol·mol−1 CO2 had greater number of floral buds and flowers than those cultivated under 400 μmol·mol−1 CO2, regardless of EC. Floral buds and flowers were not linearly increased by increasing EC, regardless of CO2 concentration. Flowering time was faster in plants cultivated under 800 μmol·mol−1 CO2. Altogether, these results suggest that an elevated atmospheric CO2 concentration positively affects the flower spike length and the number of lateral branches, floral buds, and flowers of Phalaenopsis and also indicate that nutrient levels can be adjusted to improve the growth of obligate CAM plants.