A deficiency in selenium(Se) in the human diet is a worldwide problem. The intake of Se-rich vegetables can be a safe way to combat Se deficiency for humans. However, most leafy vegetables can accumulate a high conten...A deficiency in selenium(Se) in the human diet is a worldwide problem. The intake of Se-rich vegetables can be a safe way to combat Se deficiency for humans. However, most leafy vegetables can accumulate a high content of nitrates, which poses a potential threat to human health. Light is an important environmental factor that regulates the uptake and distribution of mineral elements and nitrogen metabolism in plants. However, the effects of Se forms and light conditions, especially light spectra, on the uptake and translocation of Se and on nitrate reduction are poorly understood. In this study, lettuce(Lactuca sativa L.) was treated with exogenous Se applied as selenate(10 mmol L^-1) and selenite(0.5 mmol L^-1) and grown under five different light spectra: fluorescent light(FL), monochromatic red LED light(R), monochromatic blue LED light(B), and mixed red and blue LED light with a red to blue light ratio at 4(R/B=4), 8(R/B=8), and 12(R/B=12), respectively. The effects of light spectra and Se forms on plant growth, photosynthetic performance, Se accumulation and nitrate reduction were investigated. The results showed that the light spectra and Se forms had significant interactions for plant growth, foliar Se accumulation and nitrate reduction. The Se concentration and nitrate content in the leaves were negatively correlated with the percentage of red light from the light sources. Compared to Se applied as selenite, exogenous Se applied as selenate was more effective in reducing nitrate via promoting nitrate reductase and glutamate synthase activities. The lowest nitrate content and highest plant biomass were observed under R/B=8 for both the selenate and selenite treatments. The significant effect of the light spectra on the root concentration factor and translocation factor of Se resulted in marked variations in the Se concentrations in the roots and leaves. Compared with FL, red and blue LED light led to significant decreases in the foliar Se concentration. The results from this study suggest that the light spectra can contribute to Se distribution and accumulation to produce vegetables with better food quality.展开更多
A series of YAG：Ce,Tb phosphors were synthesized by vacuum sintering method.Moreover,their spectral properties,thermal quenching behaviors and color rendering properties were investigated systematically.The photolumi...A series of YAG：Ce,Tb phosphors were synthesized by vacuum sintering method.Moreover,their spectral properties,thermal quenching behaviors and color rendering properties were investigated systematically.The photoluminescence emission spectra of YAG：Ce,Tb show a great red shift compared with that of YAG：Ce.Direct energy transfer from Tb^（3＋） to Ce^（3＋） ions is verified based on the analysis of different photoluminescence spectra.The quenching temperature for Tb^（3＋）-doped YAG：Ce phosphors is about 490 K.The thermal activation energy is estimated to be 0.18 and 0.291 eV for Tb^（3＋）-doped YAG：Ce and YAG：Ce phosphors,respectively.The smaller activation energy for Tb^（3＋）-doped YAG：Ce means a more rapid nonradiative transition from 5d to 4f state,thus resulting in the lower quenching temperature.In addition,white LEDs with improved color rendering properties are achieved by using modified YAG：Ce,Tb phosphors.展开更多
基金financially supported by the Central Public Interest Science Institute Basal Research Fund (Y2019xk21-01)the Nottingham Trent University Q&R Fund, UK (01ARE RA 926)the Key Projects of Ningxia Key R&D Program Fund, China (2018BBF02012)
文摘A deficiency in selenium(Se) in the human diet is a worldwide problem. The intake of Se-rich vegetables can be a safe way to combat Se deficiency for humans. However, most leafy vegetables can accumulate a high content of nitrates, which poses a potential threat to human health. Light is an important environmental factor that regulates the uptake and distribution of mineral elements and nitrogen metabolism in plants. However, the effects of Se forms and light conditions, especially light spectra, on the uptake and translocation of Se and on nitrate reduction are poorly understood. In this study, lettuce(Lactuca sativa L.) was treated with exogenous Se applied as selenate(10 mmol L^-1) and selenite(0.5 mmol L^-1) and grown under five different light spectra: fluorescent light(FL), monochromatic red LED light(R), monochromatic blue LED light(B), and mixed red and blue LED light with a red to blue light ratio at 4(R/B=4), 8(R/B=8), and 12(R/B=12), respectively. The effects of light spectra and Se forms on plant growth, photosynthetic performance, Se accumulation and nitrate reduction were investigated. The results showed that the light spectra and Se forms had significant interactions for plant growth, foliar Se accumulation and nitrate reduction. The Se concentration and nitrate content in the leaves were negatively correlated with the percentage of red light from the light sources. Compared to Se applied as selenite, exogenous Se applied as selenate was more effective in reducing nitrate via promoting nitrate reductase and glutamate synthase activities. The lowest nitrate content and highest plant biomass were observed under R/B=8 for both the selenate and selenite treatments. The significant effect of the light spectra on the root concentration factor and translocation factor of Se resulted in marked variations in the Se concentrations in the roots and leaves. Compared with FL, red and blue LED light led to significant decreases in the foliar Se concentration. The results from this study suggest that the light spectra can contribute to Se distribution and accumulation to produce vegetables with better food quality.
基金supported by the National Natural Science Foundation of China(51272282,51302311)the Beijing Committee of Science and Technology(Z13111000280000)the Education Commission of Beijing(2011010329)
文摘A series of YAG：Ce,Tb phosphors were synthesized by vacuum sintering method.Moreover,their spectral properties,thermal quenching behaviors and color rendering properties were investigated systematically.The photoluminescence emission spectra of YAG：Ce,Tb show a great red shift compared with that of YAG：Ce.Direct energy transfer from Tb^（3＋） to Ce^（3＋） ions is verified based on the analysis of different photoluminescence spectra.The quenching temperature for Tb^（3＋）-doped YAG：Ce phosphors is about 490 K.The thermal activation energy is estimated to be 0.18 and 0.291 eV for Tb^（3＋）-doped YAG：Ce and YAG：Ce phosphors,respectively.The smaller activation energy for Tb^（3＋）-doped YAG：Ce means a more rapid nonradiative transition from 5d to 4f state,thus resulting in the lower quenching temperature.In addition,white LEDs with improved color rendering properties are achieved by using modified YAG：Ce,Tb phosphors.
