Co-effectiveness of Supplemental Lighting and Irrigation in Conjunction with Compensation for Midday Depression of Photosynthesis of Cut Roses

Plants grow better in circadian conditions that correspond to natural environments. However, to increase cut rose productivity, supplemental lighting was applied during night period, which might reset the circadian rhythms of the rose crops. Also, previous study indicated that drought stress occurred in none-irrigation regime under nocturnal supplemental lighting. To investigate the effect of supplemental lighting and irrigation during night on diurnal photosynthetic rate, cut rose ‘Charming Black’ was subjected to three treatment: T_Control (without supplemental lighting), T_SL×NI (PAR 90 without irrigation during night) and T_SL×I (PAR 90 with irrigation once per hour). Diurnal photosynthetic rate showed an increasing tendency from 9:00 am and the highest value occurred from 11:00 h to 14:00 h. Then photosynthetic rate decreased from 15:00 h and then remained steady in three treatment conditions. Compared with T_Control, T_SL×NI demonstrated higher photosynthetic rate during night due to supplemental lighting. Nonetheless, from 9:00 to 15:00, photosynthetic rate was lower than T_Control. Under irrigation condition T_SL×I, photosynthetic rate increased by 4.96 μmolm^-2·s^-1 compared with T_Control at 13:00 h. Under T_SL×NI, photosynthetic rate peak appeared earlier (at about 11:00 h) than T_SL×I condition (13:00 h). The Co-effect_S-I indicated that irrigation and supplemental lighting compensate for each other to promote the photosynthesis.