Temperature drop improved responses of greenhouse fruit vegetables to long photoperiod of supplemental lighting
It is well known that long photoperiods of supplemental lighting cause photo-injury such as leaf chlorosis and necrotic spotting in greenhouse fruit vegetables such as tomatoes and sweet peppers. This photo-injury has limited the application of long photoperiods of supplemental lighting and the yield increase by supplemental lighting, in year-round greenhouse vegetable production. In our previous study, we found that a temperature drop with dynamic temperature integration (TI) can promote the translocation of photo-assimilates from leaf to fruit and thus has the potential to reduce photo-injury and improve the response of greenhouse fruit vegetables to long photoperiods of supplemental lighting. Therefore, we initiated this study in 2013 with the aim to investigate the interactions between photoperiods and temperature control strategies for improving the response of greenhouse vegetables to long photoperiods of supplemental lighting including both HPS (high pressure sodium) and LED intra-canopy lighting. The study was conducted over 3 winters (from 2013 to 2016) in 8 greenhouse compartments, each with 50 m2 of growing area. Two photoperiods (control - 16 or 17 h; and long photoperiod - 20 or 21 h) of overhead HPS lighting and two temperature integration strategies (control TI - no temperature drop and dynamic TI with a temperature drop to 13.5°C for tomatoes or 15.5°C for sweet peppers at the end of photoperiod) were applied in the 8 compartments (2 complete replications). Four intra-canopy LED photoperiods (0, 16, 20 and 22 h on tomato or 0, 17, 21 and 24 h on sweet pepper) were applied to the 4 plots inside each compartment. Dynamic TI with temperature drop had the same 24-h average temperature as control TI; the low temperature during the drop period was compensated with higher temperature in other periods over a day (24-h period). Dynamic TI with temperature drop significantly reduced photo-injury and increased fruit yield at the long photoperiods for both tomatoes and sweet peppers. It also reduced the heating energy use during the cold months of winter. Therefore, dynamic temperature integration with temperature drop is an energy-efficient climate control strategy for improving the response of greenhouse tomatoes and sweet peppers to long photoperiods of supplemental lighting in year-round greenhouse fruit vegetable production.
Hao, X., Zhang, Y., Guo, X., Little, C., Zheng, J.M. and Khosla, S. (2017). Temperature drop improved responses of greenhouse fruit vegetables to long photoperiod of supplemental lighting. Acta Hortic. 1182, 185-192
Solanum lycopersicum, Capsicum annuum, high pressure sodium lamp, intra-canopy lighting, light emitting diodes (LEDs)