Effect of Low Temperature, Plant Age, and Photoperiod on the Photosynthesis of Phalaenopsis Hybrids

Abstract

This study was conducted to examine the low temperature effects under different vegetative growth stage and photoperiod effects on photosynthesis in Phalaenopsis hybrids. In Experiment 1, micropropagated clones of Phalaenopsis Hwasu 3551 (HS) and White Red Lip (WR) were acclimated for 4 weeks. . The photoperiod was provided by 12 h with a photosynthetic photon flux density of 110 ± 10 µmol·m-2·s-1 during the day (06:00~18:00). Plants were grown in a growth chamber at day/night temperatures of 28/26°C (high temperature, HT). Plants were transferred to 21/19oC (low temperature, LT) after 0 (1-month-old), 2 (3-month-old), and 4 months (5-month-old) of cultivation at HT. In Experiment 2, for determining photoperiod effect, 1-month-old plants of Phalaenopsis Hwasu 355 were grown under short day (SD, 06:00~14:00), intermediate day (MD, 06:00~18:00), long day (LD, 06:00~22:00), and night interruption (NI, 06:00~18:00 + 22:00~02:00). Vegetative growth and diurnal CO2 uptake rate of plants under each treatment were measured. Under all treatments, three Phalaenopsis hybrids showed typical CAM pathway, which is divided into Phase I to IV by CO2 exchange between leaf and air. When plants were transferred to LT, daily total net CO2 uptake and growth rate decreased. In the plants transferred to LT at 3-month-old stage (after 2 months of cultivation at HT), CO2 uptake rate during Phase III decreased to -1.36 and -0.60 µmol·m-2·s-1 in HS and WR, respectively, indicating CO2 leakage. CO2 leakage during Phase III induced the decrease of daytime total net CO2 uptake and vegetative growth rate. In addition, when the plants were transferred to LT at 1-month-old stage (after 0 month of cultivation at HT), the number of new leaves significantly decreased. However, when 5-month-old plants were transferred to LT, decrease of the number of new leaves was not observed and only leaf length decreased. Under MD, leaf length, leaf width, and leaf area were significantly higher than LD and NI conditions. These results indicated that the effect of low temperature on photosynthesis and vegetative growth was small in 5-month-old plant, and vegetative growth was maintained. Also, vegetative growth rate under MD was higher than other photoperiods. As a result, maintaining high temperature (above 26oC) with 12h/12h photoperiod is important during cultivation of young Phalaenopsis (1 and 3-month-old plant). This approach can helpful to schedule or strategize high quality Phalaenopsis cultivation and reduce damages from low temperature with energy savings.