Productivity and photosynthetic characteristics of heat-resistant and heat-sensitive recombinant inbred lines (RILs) of Lactuca sativa in response to different durations of LED lighting

摘要

Many studies have shown that longer photoperiods result in increased rates of plant growth. This study investigated the impact of different photoperiods of red- and blue-LED lighting on the growth, as well as, photosynthetic characteristics of heat-resistant (HR) and heat-sensitive (HS) RILs of Lactuca sativa grown in a vertical farming system. Lettuce plants were grown under three different photoperiods (12, 16 and 18 h) of red- (85%) and blue- (15%) LED lighting, at a mean photosynthetic photon flux density (PPFD) of 300 umol m2 s1. 27 days after transplanting, both HR-and HS-RIL plants had significantly higher shoot and root fresh (FW) and dry (DW) weights, leaf number and total leaf area (TLA) when subjected to extended photoperiods of 16 and 18 hthan the normal 12-h photoperiod. Highest growth parameters were observed for the longest photoperiod of 18 h. However, photosynthetic properties were not greatly enhanced under the extended photoperiods of 16 and 18 h - only chlorophyll (Chi) a/b ratiowas increased. Light saturated photosynthetic C02 assimilation (Asat) and stomatal conductance [gs sat) among plants exposed to different durations of LED lighting showed no significant difference among the various photoperiods. Though longer photoperiods resulted in increased total carbon assimilation, this would have been due to the plants having a larger TLA. The decrease in soluble and insoluble sugar concentrations in lettuce leaves, under longer photoperiods, was most probably due to the dilutionof carbohydrates as a result of increased leaf number and total leaf area. Thus, the results suggest a lack of feedback inhibition of photosynthetic end products in the leaves of lettuce plants, despite its exposure to longer photoperiods.