Salinity and light quality effect on growth, water relations, photosynthetic performance and nutritional quality of aeroponically grown edible mesembryanthemum crystallinum and portulaca oleracea
Authors:   , Leng Su Yee 
Published: October 2024

Growing halophytes using saline water would be a feasible solution to the declining availability of fresh water. On aeroponically grown edible halophytes Mesembryanthemum crystallinum and Portulaca oleracea, this study investigated 1) the impacts that different percentage of artificial seawater (ASW) had on the plant growth, water relations, photosynthetic performance and nutritional quality; 2) the interactive effects of ASW and light spectrum quality on growth, water relations, photosynthetic performances and nutritional quality; and 3) the effects of salt priming under effective LED lighting on growth and nutritional quality. Both M. crystallinum and P. oleracea grew under LED of R/B 2.2 in 10%, 20%, 30%, 40%, 60%, 80% and 100% ASW for the first objective. Shoot and root biomass generally decreased with increasing saline concentration for both plants. However, M. crystallinum exhibited a high level of salt tolerance and grew well in 100% ASW while P. oleracea were not able to survive in 100% ASW. It was found that 10% ASW was the most favorable condition tested for the growth of both plants. When severely salt stressed at 60% ASW, both plants induced CAM photosynthesis to manage its water status. The findings of this study suggest that M. crystallinum had a higher salt tolerance, and possibly equipped with more robust mechanisms to alleviate the oxidative stress, than P. oleracea. As for the second objective, both plants were grown under R/B LED ratio of 0.9 and 2.2 in 10% and 40% ASW. M. crystallinum grown in 10% ASW under R/B 2.2. and P. oleracea grown in 10% ASW under R/B 0.9 had higher productivities. This had once again proven that low salinity favours photoassimilate accumulation. Both plants relied heavily on proline to counter oxidative stress at higher salinity concentration of 40% ASW under both light conditions. There were no clear correlation between antioxidant enzymes and dietary minerals studied with salinity treatment and light conditions as they could possibly be dependent on species and other environmental conditions. Large amount of Na+ was found in both plants grown in 40% ASW regardless of light conditions. Ultimately, for the third objective, the plants were grown under R/B LED ratio of 2.2. The seedlings were grown in 10% ASW for 10 days (I) after transplant where the first harvest occur. From day 11 to 16 of transplant, both types of plants were exposed to 4 different treatments before harvesting on day 16, i.e. II: 10% ASW; III: 80% ASW; IV: 40% ASW ⟹ 80% ASW; V: 40% ASW ⟹ 60% ASW ⟹ 80% ASW. Primed M. crystallinum had higher productivities than those that were not primed. However, priming had not much effect on the productivities on P. oleracea. Priming resulted in enhanced proline accumulation, Asc concentration, soluble sugars and antioxidant enzymes activities in M. crystallinum. However, it did not have much effect on proline accumulation and antioxidant enzyme activities in P. oleracea. A reduction of Na+ was observed both plants when primed, and once again, no distinct trends were observed between dietary minerals and salt priming.