Mesembryanthemum crystallinum is a succulent, facultative crassulacean acid metabolism (CAM) plant. Plant growth and photosynthetic characteristics were studied when M. crystallinum plants were grown indoor under light emitting diodes (LED)-lighting with adequate water supply. Plants were cultured aeroponically for a 16-h photoperiod at an equal photosynthetic photon flux density of 350 μmol m-2 s-1 under different red:blue LED ratios: (1) 100:0 (0B); (2) 90:10 (10B); (3) 80:20 (20B); (4) 70:30 (30B); (5) 50:50 (50B); and (6)100:0 (100B). M. crystallinum grown under 10B condition had the highest shoot and root biomass and shoot/root ratio while those grown under 0B condition exhibited the lowest values. Compared to plants grown under 0B condition, all other plants had similar but higher total chlorophyll (Chl) and carotenoids (Car) contents and higher Chl a/b ratios. However, there were no significant differences in Chl/Car ratio among all plants grown under different red- and blue-LEDs. Photosynthetic light use efficiency measured by photochemical quenching, non-photochemical quenching, and electron transport rate, demonstrated that plants grown under high blue-LED utilized more light energy and had more effective heat dissipation mechanism compared to plants grown under 0B or lower blue-LED. Statistically, there were no differences in photosynthetic O2 evolution rate, light-saturated CO2 assimilation rate (Asat), and light-saturated stomatal conductance (gssat) among plants grown under different combined red- and blue-LEDs but they were significantly higher than those of 0B plants. No statistically differences in total reduced nitrogen content were found among all plants. For the total soluble protein, all plants grown under different combined red- and blue-LEDs had similar values but they were significantly higher than that of plants grown under 0B condition. However, plants grown under higher blue-LEDs had significant higher ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) protein than those plants grown under lower blue-LED. High Asat and gssat but very low CAM acidity of all M. crystallinum plants during light period, imply that this facultative CAM plant performed C3 photosynthesis when supplied with adequate water. Results of this study suggest that compared to red- or blue-LED alone, appropriate combination of red- and blue-LED lighting enhanced plant growth and photosynthetic capacities of M. crystallinum.

A major challenge for growing vegetables in an indoor vertical farming system will be supplying not only sufficient quantity but also quality of light. It has been reported that yield of crops is enhanced under appropriate combination of red and blue light compared with red light alone. This project aims to investigate the effects of different combinations of red and blue. Plants were cultured for a 12-h photoperiod at 210 µmol•m -2 •s -1 photosynthetic photon flux density (PPFD) under different combinations of red (R) and blue (B) light-emitting diodes (LED). The R:B-LED ratios are: 1) 100:0 (0B); 2) 92:8 (8B); 3) 84:16 (16B) and; 4) 76:24 (24B). All combined RB-LEDs significantly increased light-saturated photosynthetic CO2 assimilation rate (Asat), stomatal conductance (gs sat) and productivity compared with those under 0B. Results suggested that 16B was the most suitable combination of LEDs to achieve the highest productivity for B. alboglabra. To further substantiate these results, comparative studies were conducted under equal photoperiod and PPFD among 16B (RB-LED), white LED (RBW-LED) and high-pressure sodium (HPS) lamps. Shoot, root biomass, leaf number, leaf mass per area and Asat were higher in plants under HPS lamps and RB-LED, than under RBW-LED. However, gs sat was lower under RB-LED and RBW-LED, than under HPS lamps. Plants under RB-LED had higher electron transport rate and photochemical quenching but lower non-photochemical quenching than those under RBW-LED and HPS lamps. Thus, these results more conclusively affirmed that 16B was the most suitable light source to achieve the highest photosynthetic capacities. The findings of this study could also be used in vertical farming to achieve the highest productivity of vegetable crops such as B. alboglabra within the shortest growth cycle with reduced energy consumption.

LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 mol m −2 s −1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress.

Although tropical high ambient temperature and humidity severely reduced the productivity of temperate plants, temperate vegetable crops such as lettuce have been successfully grown in Singapore by only cooling its root-zone. In this paper, a cool Meditteranean vegetable, Eruca sativa, was studied to understand how different RZTs can impact its shoot productivity, photosynthesis and nutritional quality. All plants were cultivated using aeroponic systems in a tropical greenhouse under hot ambient conditions where roots were subjected to four different root-zone temperatures (RZTs) of 20˚C-RZT, 25˚C-RZT, 30˚C-RZT and fluctuating ambient temperatures ranged from 25˚C to 38˚C [25˚C/38˚C (ambient)]-RZT. Parameters studied include shoot fresh weight (FW), photosynthetic gas exchange, midday chlorophyll (Chl) fluorescence F v /F m ratio, Chl fluorescence photochemical quenching (qP), non-photochemical quenching (qN) and electron transport rate (ETR), total phenolic compounds and mineral content such as potassium (K), calcium (Ca), magnesium (Mg) and iron (Fe). Among the 4 different RZT treatments, E. sativa plants grown under ambient-RZT (25/38˚C-RZT) had the lowest shoot and root FW while those plants grown under 20˚C-RZT had highest productivity of shoot and root. However, there were no significant differences in shoot and root FW in plants grown at 25˚Cand 30˚C-RZT. Compared to plants grown under 25˚C/38˚C (ambient-RZT), lightsaturated photosynthetic CO 2 assimilation rate (A sat ) and stomatal conductance (g ssat ) were similarly higher in 20˚C-, 25˚C-and 30˚C-RZT. All plants had midday Chl fluorescence F v /F m ratio lower than <0.8 ranged from 0.785 to 0.606 with the highest and lowest ratios recorded in 20˚C-RZT and ambient-RZT plants, respectively. These results indicate that cooling the RZ of E. sativa plants protected their PS II from photoinactivation during midday in the greenhouse. There were no significant dif-How to cite this paperOpen Access J. He et al. 1994 ferences observed in photochemical quenching (qP), non-photochemical quenching (qN) and electron transport rate among plants grown under 20˚C-, 25˚C-and 30˚C-RZT. However, plants grown under ambient-RZT had lower qP, qN and ETR compared to all other plants. E. sativa at 20˚C-RZT with the best developed roots had the highest dietary mineral (K, Mg, Ca and Fe) contents but lower total phenolics content. In contrast, ambient-RZT, plants with poorly developed roots had the lowest mineral content but highest total phenolic content. The results of this study suggest that cooling of roots is a feasible method for the cultivation of E. sativa in the tropic, which enhances the content of dietary minerals in shoots.

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