LED quality impacts on plant growth and photosynthetic light use efficiency of halophyte vegetable Mesembryanthemum crystallinum grown under two saline conditions

Abstract

There is very little study on the effects of LED quality on Mesembryanthemum crystallinum grown under different salinities. In this study, M. crystallinum was grown under red/blue (R/B) LED ratios of 0.9, 1.6. 2.0 and 2.8 with 100 and 500 mM NaCl and exposed to the same level of photosynthetic photon flux density, PPFD (290 µmol m‑2 s‑1, 12 h photoperiod). Fourteen days after transplanting, plants with 100 mM NaCl had significantly higher values of growth parameters including shoot and root fresh weight, total leaf area and specific leaf area than with 500 mM NaCl. Grown with 100 mM NaCl under R/B 0.9, M. crystallinum had significantly lower shoot FW and total leaf area than under other R/B ratios. However, LED quality did not seem to affect the growth parameters of M. crystallinum grown with 500 mM NaCl. All plants had similar higher leaf succulence and water content but lower leaf dry matter content with 100 mM NaCl than with 500 mM NaCl. Crassulacean acid metabolism (CAM) acidity of plants grown with 500 mM NaCl was about 4-fold higher than with 100 mM NaCl, indicating induction and stimulation of CAM photosynthesis. Chlorophyll fluorescence Fv/Fm ratios were greater than 0.8 for all plants, suggesting that maximum efficiency of PSII was unaffected by LED quality and salinity. M. crystallinum grown with 500 mM NaCl had lower electron transport rate, ETR but higher non-photochemical quenching, NPQ than with 100 mM NaCl, implying that photosynthetic light use efficiency was affected when switching C3 to CAM photosynthesis under high salt stress. M. crystallinum grown with100 mM NaCl had higher photochemical quenching, qP and ETR under R/B 0.9 than under R/B 2.8 and all plants with 500 mM NaCl. In conclusion, LED quality had different impacts on photosynthetic light-use efficiency of M. crystallinum grown under different salinities and thus resulting in different growth and productivity.