Effects of artificial light sources on growth and phytochemicals content in green oak lettuce

ABSTRACT The artificial light source is one of the most important factors in a controlled environment for vegetable production. It could provide new opportunities to improve growth and increase phytochemicals content in vegetables. Therefore, this study focused on the effects of artificial light sources on growth and phytochemicals in green oak lettuce (Lactuca sativa). The plants were grown under growth chamber with three artificial light sources, namely bar-LED (the 1:1:1 ratio of blue 460 nm : red 630 nm : red 660 nm), bulb-LED (the 2:1:1 ratio of blue 460 nm : red 630 nm : red 660 nm), and fluorescent lamp (FL) (the wavelength range 380-700 nm) for 4 weeks. The quality of bar-LED light was better than either bulb-LED or FL, when assessed by the parameters of photosynthetically active radiation (PAR), photosynthetic photon flux density (PPFD, 400-700 nm), PPFD-B (blue, 400-500 nm), PPFD-R (red, 600-700 nm), the yield photon flux density (YPFD), and the color of red. However, shoot and root (fresh and dry mass), leaf area, leaf number, and shoot/root ratio did not significantly differ between plants grown under bar-LED and bulb-LED, but they were significantly higher than plants grown under FL. Bulb-LED and bar-LED induced larger dry mass of the plants than FL. The dry mass per mole of artificial lighting was highest in plants grown under bar-LED. On the other hand, the fresh mass per mole of artificial lighting was highest in plants grown under bulb-LED. As regards power consumption, bar-LED provided the lowest consumption with 44.4% energy saving over the FL. Total phenolic content, 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and 2,2-diphenylpicrylhydrazyl (DPPH) activities were highest in plants grown under bar-LED. FL lighting gave the least contents of chlorophyll a and chlorophyll a + b. However, chlorophyll b and carotenoid contents did not significantly differ among the treatments. Thus, the results suggested that bar-LED has the potential to improve energy saving, and both growth and phytochemicals content of green oak lettuce grown in a controlled environment of vegetable production.

摘要
人工光源是蔬菜设施栽培可控环境中最为关键的影响因素之一，可为改善蔬菜生长、提升植物次生代谢物含量提供新途径。本研究以绿橡叶生菜（Lactuca sativa）为试材，探究不同人工光源对其生长及植物次生代谢物含量的影响。试验在生长箱内设置3种人工光源处理：条形LED（bar-LED，蓝光460 nm∶红光630 nm∶红光660 nm配比为1∶1∶1）、球泡型LED（bulb-LED，蓝光460 nm∶红光630 nm∶红光660 nm配比为2∶1∶1）以及荧光灯（fluorescent lamp, FL，波长范围380~700 nm），栽培周期为4周。
通过光合有效辐射（photosynthetically active radiation, PAR）、光合光子通量密度（photosynthetic photon flux density, PPFD，400~700 nm）、蓝光光合光子通量密度（PPFD-B，400~500 nm）、红光光合光子通量密度（PPFD-R，600~700 nm）、产额光子通量密度（yield photon flux density, YPFD）及红光色度等指标评估光源品质，结果显示条形LED的光源品质优于球泡型LED与荧光灯。
相较于荧光灯处理，条形LED与球泡型LED处理的生菜地上部、地下部鲜干质量、叶面积、叶片数以及根冠比均无显著差异，但二者的上述指标均显著高于荧光灯处理；且条形LED与球泡型LED处理的生菜干物质积累量显著高于荧光灯。单位摩尔人工光照下的干物质产量以条形LED处理最高，而单位摩尔人工光照下的鲜物质产量则以球泡型LED处理最高。
能耗方面，条形LED的能耗最低，较荧光灯节能44.4%。条形LED处理的生菜总酚含量、2,2'-联氮-双(3-乙基苯并噻唑啉-6-磺酸)（ABTS）自由基清除活性与2,2-二苯基-1-苦肼基（DPPH）自由基清除活性均为最高。荧光灯处理的生菜叶绿素a及叶绿素a+b含量最低，但叶绿素b与类胡萝卜素含量在各处理间无显著差异。
综上，本研究结果表明，条形LED具备提升设施蔬菜栽培节能效率、改善绿橡叶生菜生长及植物次生代谢物含量的应用潜力。