Although cooling their rootzone allows year-round (temperate) vegetable production in Singapore's warm climate, these crops have frequently experienced increasingly unpredictable cloudy and hazy weather. Supplementary lighting with light-emitting diodes (LEDs) could be used to reduce the impacts of low light intensity. This study investigated the responses of temperate Cos lettuce (Lactuca sativa L.) to different quantities (photosynthetic photon flux density, PPFD of 0, 150, 300 µmol m⁻² s⁻¹) of supplementary LED lightings in the tropical greenhouse. Increasing light intensity significantly increased total leaf area, shoot and root fresh weight (FW) and dry weight (DW), total chlorophyll (Chl) and carotenoids (Car) contents, light-saturated photosynthetic CO₂ assimilation rate (A_sat) and transpiration rate (T_r). There were no significant differences in F_v/F_m ratio, total reduced nitrogen, specific leaf area (SLA) and PSII concentration among the three light treatments. However, there was an increasing trend with increasing light intensity for Chl a/b ratio, net photosynthetic O₂ evolution rate (P_N), cytochrome b₆f (Cyt b₆f), leaf total soluble protein and Rubisco concentrations. This study provides the basic understanding of photosynthetic apparatus and capacity of temperate crops grown under different supplementary LED lightings in the tropical greenhouse.

尽管根区冷却可以在新加坡温暖的气候下实现全年（温带）蔬菜生产，但这些作物经常经历越来越难以预测的多云和雾霾天气。可以使用发光二极管 (LED) 辅助照明来减少低光强度的影响。本研究调查了温带生菜 ( Lactuca sativa L.) 对热带温室中不同量（光合光子通量密度，PPFD 为 0、150、300 µmol m ⁻² s ⁻¹ ）补充 LED 照明的响应。增加光照强度显着增加总叶面积、茎和根鲜重(FW)和干重(DW)、总叶绿素(Chl)和类胡萝卜素(Car)含量、光饱和光合CO ₂同化率( A _sat )和蒸腾量_率（ Tr ） 。 3个光处理间F _v / F _m比值、总还原氮、比叶面积(SLA)和PSII浓度无显着差异。然而，叶绿素a / b比值、净光合O ₂演化率( P _N )、细胞色素b ₆ f (Cyt b ₆ f)、叶片总可溶性蛋白和Rubisco浓度随光照强度的增加呈增加趋势。这项研究提供了对热带温室中不同 LED 辅助照明下生长的温带作物的光合机构和能力的基本了解。