Background: Welsh onions are often affected by stressful environments, such as high light and drought, during summer cultivation, which hinders their growth. To date, few studies have focused on leaf photosynthesis of Welsh onions during summer. We used carbon dioxide assimilation and OJIP transient and MR curves to analyze the photosynthetic characteristics of Welsh onions. Results: The results showed that strong light and drought could lead to a decrease in leaf pigment content. Simple high light stress caused a decrease in the net photosynthetic rate through stomatal limitation, while the simple drought treatment and the two stress factors combined caused a nonstomatal limitation. PSII energy distribution indicated that strong light and drought stress reduced the photochemical quantum efficiency of PSII. OJIP curve analysis showed that FO and FJ were increased, Fm was decreased, and a distinct K-phase was induced. In addition, OJIP parameters, including RC/CSO, TRO/ABS, ETO/TRO, and PIABS, were significantly reduced. MR analysis showed that strong light and drought stress blocked MR transients, leading to a gradual decrease in VPSI and VPSII-PSI. Conclusions: In general, the photosynthesis of Welsh onion was inhibited by high light and drought, which destroyed the receptor and donor side of PSII and reduced the electron transport capacity of PSII and PSI.
The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance. Because of this, in recent years LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to light quality. The influence of light quality on photosynthesis needs to be further explored to provide theoretical guidance for the adjustment of the light environment in industrial crop production. This study tested the effects of different qualities of LED lighting (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photosynthetic photon flux density (300 μmol/m2·s) on the growth and development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) plants. The results showed that the plant height, leaf area, and fresh weight of plants in the W and B treatments were significantly higher than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate (Pn) in the W treatment were significantly higher than those in the monochromatic light treatments, while the transpiration rate (E) and stomatal conductance (Gs) were the highest in the B treatment, and the intercellular CO2 concentration (Ci) was the highest in the Y treatment. Among the chlorophyll fluorescence characteristics tested, the non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, while the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv'/Fm'), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR) all differed among treatments in the following order: W > B > R > G > Y. Both leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. In summary, in addition to W light, B light significantly improved the photosynthetic efficiency of Welsh onion, whereas Y light significantly reduced the photosynthetic efficiency of this plant.
Background: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance. Because of this, in recent years LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to light quality. The influence of light quality on photosynthesis needs to be further explored to provide theoretical guidance for the adjustment of the light environment in industrial crop production. This study tested the effects of different qualities of LED lighting (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m2·s) on the growth and development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) plants. Results: The results showed that the plant height, leaf area, and fresh weight of plants in the W and B treatments were significantly higher than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate (Pn) in the W treatment were significantly higher than those in the monochromatic light treatments, while the transpiration rate (E) and stomatal conductance (Gs) were the highest in the B treatment, and the intercellular CO2 concentration (Ci) was the highest in the Y treatment. Among the chlorophyll fluorescence characteristics tested, the non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, while the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv'/Fm'), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR) all differed among treatments in the following order: W > B > R > G > Y. Both leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. Conclusions: In summary, in addition to W light, B light significantly improved the photosynthetic efficiency of Welsh onion, whereas Y light significantly reduced the photosynthetic efficiency of this plant.
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