Response of Chlorophyll Fluorescence Characteristics and Dissolved Organic Matter for Marine Diatom Skeletonema dohrnii under Stress from Penicillin and Zn2+

Skeletonema dohrnii is a good model diatom for studying environmental stress and has promising applications and prospects in various fields. Antibiotics and heavy metals are commonly exceeded in the nearshore marine habitats. In this work, we investigated the effects of an antibiotic (penicillin, 2 µg/L) and a heavy metal ion (Zn2+, 10 µmol/L) stress on marine diatom S. dohrnii, mainly using excitation-emission matrices (EEMs) fluorescence methods and OJIP test. Results indicated that algal cells grown with the antibiotic showed higher biomass, specific growth rate, doubling time, chlorophyll a, and chlorophyll fluorescence variables. Moreover, excess zinc had negative effects on S. dohrnii. We found that zinc not only inhibited the relative photosynthetic electron transfer efficiency but also reduced the Chl a content, which ultimately affected algal growth and organic matter production. In addition, the combined effect of penicillin and Zn2+ further affected the physiological state of S. dohrnii. The dissolved organic matter (DOM) characteristics of the four cultures were also different, including fluorescence indices (fluorescence index, biological index, β/α, and humification index) and fluorescence peaks (peaks A, C, M and T). In brief, characterization of chlorophyll fluorescence characteristics and DOM-related variables are important for understanding the effects of environmental stress on microalgae.

Leaf morphology and chlorophyll fluorescence characteristics of mulberry seedlings under waterlogging stress

Because of its high flooding tolerance, in recent years, mulberry has become a tree species that is used in plant restoration in impact zones in reservoir areas. Therefore, 3-year-old potted forage mulberry seedlings were used to investigate the mechanism of mulberry adaptation to flooding stress. An indoor simulated flooding method was adopted to study the morphology of mulberry seedling leaves and the changes in leaf chlorophyll fluorescence parameters and fluorescence imaging under different flooding times and depths. The results showed that the leaves of mulberry seedlings treated with shallow submergence remained healthy during the flooding period, while the leaves of mulberry seedlings treated with half submergence and full submergence showed different degrees of waterlogging symptoms in the middle and late flooding periods and formed adventitious roots at the base of the stem. Most of the chlorophyll fluorescence parameters decreased at the beginning of flooding, but the steady-state degree of closure of PS II reaction centres (1-qP_Lss) increased significantly. In the later stage of flooding, the fluorescence parameters showed relatively stable trends. Based on these results, we conclude that mulberry has high flooding tolerance due to a combination of morphological and physiological responses.

New Insight on Low-K Lettuce: From Photosynthesis to Primary and Secondary Metabolites

With the increase in dialysis patients worldwide, the demand for low-K vegetables is growing. Thus, a type of lettuce with a low-K content has been marketed in Japan. To learn more about low-K vegetables, information is needed on the physiological differences between these vegetables and those with typical levels of potassium (K). In this study, lettuces (Lactuca sativa L.) were cultivated using two low-K management methods in an environment-controlled system. One method was based on electrical conductivity (EC) management, and the K was replaced by sodium (Na) at the end of cultivation. The other method was based on quantitative nutrient management, and the nutrients required for low-K lettuce were quantitatively supplied, but no extra Na was added. Meanwhile, lettuce with normal K concentration was cultivated with EC management as the control. Plant growth indices, leaf photosynthesis traits, chlorophyll fluorescence characteristics, concentrations of secondary metabolites (SMs), and antioxidant activity were examined to investigate the physiological effects of low-K and high-Na concentrations during low-K lettuce cultivation. Both low-K treatments significantly restrained the growth of lettuce and increased the concentration of soluble sugar. However, photosynthesis and fluorescence characteristics remained unchanged. This indicates that the biomass reduction of low-K lettuce was due to the wasteful accumulation of carbohydrates rather than the decline in photosynthesis. Concentrations of SMs were increased in the low-K lettuce. In addition, higher concentrations of Na influenced the concentration of SMs, indicating that SMs were more sensitive to environmental stress.

Photosynthetic characteristics and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) grown under different LED wavelengths

Background: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m 2 ·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion ( Allium fistulosum L.) plants. Results: Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate ( P n ) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate ( E ) and stomatal conductance ( G s ) were the highest in the B treatment, and the intercellular CO 2 concentration ( C i ) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes 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). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. Conclusions: White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Photosynthetic characteristics and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) grown under different LED wavelengths

Background: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m 2 ·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion ( Allium fistulosum L.) plants. Results: Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate ( P n ) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate ( E ) and stomatal conductance ( G s ) were the highest in the B treatment, and the intercellular CO 2 concentration ( C i ) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes 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). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. Conclusions: White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Responses of the photosynthetic characteristics and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) to different LED light qualities

Background: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to theirphotosynthetic 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 sama 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 ratein 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.