Effects of Electrical Conductivity (EC) of System Water and Vapor Pressure Deficit (VPD) on the Physiological Responses and Flowering of Kalanchoe blossfeldiana in an Aquaponic System

This study investigated the effects of system water electrical conductivity (EC) levels and the growing environment on the physiological responses (photosynthesis, SPAD value, and chlorophyll fluorescence), growth, and flowering characteristics of florist kalanchoe (Kalanchoe blossfeldiana) in a goldfish (Carassius auratus L.) aquaponic system over a time span of 140 days.The experiment was conducted at three EC levels (0.5, 1.0, and 1.5dS•m -1 ), which were maintained by regulating fish feeding rates (50% crude protein) without the addition of chemical fertilizers.During the experimental period, mean air temperatures were similar between the growth room and the control (22.4 and 22.8°C, respectively), whereas relative humidity was markedly higher in the growth room (57.7%) than in the control (32.7%), resulting in mean vapor pressure deficit (VPD) values of 1.18 and 1.98kPa, respectively, with the control peaking at 2.22-2.30kPaduring November-December.The pH of the system water remained stable within a range of 5.0-6.6, and EC was consistently maintained at designated levels without nutrient accumulation.The photosynthetic rate, stomatal conductance, and transpiration rate were more strongly influenced by the VPD than by the EC level; despite the high VPD, a continuous water supply maintained stomatal opening in the control case, resulting in photosynthetic rates 38.8-43% higher than those of the EC 1.0 growth room treatment.The maximum photochemical efficiency of photosystem II (Fv/Fm) remained stable at 0.81-0.83across all treatments, and the performance index (PI_ ABS ) was highest in the control at 140 days after