Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations

Abstract

Portulaca oleracea L. (known as purslane), is a nutritious facultative C4 halophyte. Recently, it has been successfully grown indoors under LED lightings by our team. However, basic understanding about the impacts of light on purslanes are lacking. This study aimed to investigate the effects of light intensity and duration on productivity, photosynthetic light use efficiency, nitrogen metabolism and nutritional quality of indoor grown purslanes. All plants were grown in 10% artificial seawater hydroponically under different photosynthetic photon flux densities (PPFDs) and durations and thus different daily light integrals (DLI). They are, L1 (240 µmol photon m-2 s-1, 12 h, DLI = 10.368 mol m-2 day-1); L2 (320 µmol photon m-2 s-1, 18 h, DLI = 20.736 mol m-2 day-1); L3 (240 µmol photon m-2 s-1, 24 h, DLI = 20.736 mol m-2 day-1); L4 (480 µmol photon m-2 s-1, 12 h, DLI = 20.736 mol m-2 day-1), respectively. Compared to L1, higher DLI promoted root and shoot growth and thus increased shoot productivity by 2.63-,1.96-, 3.83-folds, respectively for purslane grown under L2, L3, L4. However, under the same DLI, L3 plants (continuous light, CL) had significantly lower shoot and root productivities compared those with higher PPFDs but shorter durations (L2 and L4). While all plants had similar total chlorophyll and carotenoid concentrations, CL (L3) plants had significantly lower light use efficiency (Fv/Fm ratio), electron transport rate, effective quantum yield of PSII, photochemical- and non-photochemical quenching. Compared to L1, higher DLI with higher PPFDs (L2 and L4) increased leaf maximum nitrate reductase activity while longer durations increased leaf NO3− concentrations and total reduced nitrogen. There were no significant differences in leaf total soluble protein, total soluble sugar and total ascorbic acid concentrations in both leaf and stem regardless of light conditions. However, L2 plants had the highest leaf proline concentration but leaf total phenolic compounds concentration was higher in L3 plants instead. Generally, L2 plants had the highest dietary minerals such as K, Ca, Mg and Fe among the four different light conditions. Overall, L2 condition is the most suitable lighting strategy in enhancing productivity and nutritional quality of purslane.

Growth, Physiology and Nutritional Quality of C4 Halophyte Portulaca oleracea L. Grown Aeroponically in Different Percentages of Artificial Seawater under Different Light-Emitting Diode Spectral Qualities

“…The results of this study revealed a highly complex picture of N metabolism and nutritional quality of purslane grown in different percentages of ASW under different LED spectral qualities as there were no clear trends in their responses to the different treatments. Our recent study with purslane showed that increasing the daily light integral through the optimum combination of light intensity and photoperiod displayed positive effects on the productivity and nutritional quality of purslane [ 73 ]. The influences of LED spectral quality and salinity effects on purslane may also depend on the light intensity or daily light integral, which merit further study.…”

Simultaneous Application of Red and Blue Light Regulate Carbon and Nitrogen Metabolism, Induces Antioxidant Defense System and Promote Growth in Rice Seedlings under Low Light Stress

“…Plants mainly absorb and utilize nitrogen in soil (mainly nitrate nitrogen and ammonium nitrogen) through roots, so the development of roots directly affects plant nitrogen metabolism, and light quality can indirectly regulate plant nitrogen metabolism by affecting root growth [ 37 ]. At the same time, light quality will also directly participate in other aspects of plant nitrogen metabolism, affecting the content of physiological activities related to nitrogen metabolism (nitrate nitrogen, ammonium nitrogen, free amino acid, and soluble protein) and the activities of related nitrogen metabolism enzymes (NR, AS, GOGAT, GS) [ 45 , 46 ]. The results of the present study are that the nitrate nitrogen of XZX24 and HZY261 under the R treatment was higher than those under the B treatment ( Figure 6 A); nevertheless, ammonium nitrogen, free amino acid, and soluble protein of XZX24 and HZY261 under the B treatment were higher than those under the R treatment ( Figure 6 B–D).…”

“…Soluble protein: Soluble protein was measured by the Ren [ 46 ] method. Samples (0.1 g fresh rice leaves) were ground up in a mortar with liquid nitrogen, to which 6 mL of a phosphate buffer (pH 7.0) was added.…”

Enhancing Productivity and Improving Nutritional Quality of Subtropical and Temperate Leafy Vegetables in Tropical Greenhouses and Indoor Farming Systems

“…Compared to purslane plants grown under lower PPFD, shorter photoperiods, and thus lower DLI (240 µmol photon m −2 s −1 , 12 h, DLI = 10.368 mol m −2 day −1 ), higher DLIs (20.736 mol m −2 day −1 ) via different combinations of PPFD and photoperiods promoted root and shoot growth and thus increased shoot productivity. Higher DLIs also enhanced nutritional quality, resulting in higher accumulations of proline and total phenolic compounds as well as dietary minerals such as K, Ca, Mg, and Fe [135]. However, under the same higher DLI (20.736 mol m −2 day −1 ), different combinations of specific PPFD and photoperiod could have different effects on plant growth and the nutritional quality [136].…”

“…However, under the same higher DLI (20.736 mol m −2 day −1 ), different combinations of specific PPFD and photoperiod could have different effects on plant growth and the nutritional quality [136]. Overall, growing purslane under a PPFD of 320 µmol m −2 s −1 with 18 h photoperiod (DLI = 20.736 mol m −2 day −1 ) is the most suitable strategy for enhancing the productivity and nutritional quality of purslane [135]. However, purslane grown under the CL condition with the same DLI (240 µmol photon m −2 s −1 , 24 h photoperiod) had lower shoot and root biomass, which resulted from the lower maximal quantum efficiency of PS II (F v /F m ratios < 0.8) and lower electron transport rate, indicating photoinhibition and low light use efficiency [137].…”