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1. Selenium distribution and nitrate metabolism in hydroponic lettuce (Lactuca sativa L.): Effects of selenium forms and light spectra
BIAN Zhong-hua, LEI Bo, CHENG Rui-feng, WANG Yu, LI Tao, YANG Qi-chang
Journal of Integrative Agriculture    2020, 19 (1): 133-144.   DOI: 10.1016/S2095-3119(19)62775-9
摘要 （118）      PDF    收藏
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. 
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2. The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce (Lactuca sativa L.)
LEI Bo, BIAN Zhong-hua, YANG Qi-chang, WANG Jun, CHENG Rui-feng, LI Kun, LIU Wen-ke, ZHANG Yi, FANG Hui, TONG Yun-xin
Journal of Integrative Agriculture    2018, 17 (04): 837-846.   DOI: 10.1016/S2095-3119(17)61759-3
摘要 （586）      PDF    收藏
High nitrate (NO3−) in vegetables, especially in leaf vegetables poses threaten to human health.  Selenium (Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies.  Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses.  However, the influence of exogenous Se on NO3− accumulation in hydroponic vegetables is still not clear.  In the present study, hydroponic lettuce plants were subjected to six different concentrations (0, 0.1, 0.5, 5, 10 and 50 µmol L–1) of Se as Na2SeO3.  The effects of Se on NO3− content, plant growth, and photosynthetic capacity of lettuce (Lactuca sativa L.) were investigated.  The results showed that exogenous Se positively decreased NO3− content and this effect was concentration-dependent.  The lowest NO3− content was obtained under 0.5 µmol L–1 Se treatment.  The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate (Pn), stomatal conductance (Cs) and the transpiration efficiency (Tr) of lettuce.  The transportation and assimilation of NO3− and activities of nitrogen metabolism enzymes in lettuce were also analysed.  The NO3− efflux in the lettuce roots was markedly increased, but the efflux of NO3− from the root to the shoot was decreased after treated with exogenous Se.  Moreover, Se application stimulated NO3− assimilation by enhancing nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamate synthase enzyme (GOGAT) activities.  These results provide direct evidence that exogenous Se shows positive function on decreasing NO3− accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce.  We suggested that 0.5 µmol L–1 Se can be used to reduce NO3− content and increase hydroponic lettuce yield. 
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3. Observed Climatic Variations in the Growing Season of Field Crops in Northeast China from 1992 to 2012
LIU Yang, JIANG Wen-lai, XIAO Bi-lin, LEI Bo
Journal of Integrative Agriculture    2014, 13 (7): 1451-1461.   DOI: 10.1016/S2095-3119(14)60812-1
摘要 （1571）      PDF    收藏
To determine the potential effects of climate change on crop phenological development and productivity, an integrated analysis was conducted based on the observed climatic and phenological records of Northeast China from 1992 to 2012. A set of quality assurance procedures, including repeated record checks, agro-meteorological station selection, internal consistency checks, temporal outlier checks, spatial outlier checks, and interpolation of missing data, were designed and applied to the phenology datasets of spring maize and paddy rice. Our results indicated that almost all phenological dates of spring maize and paddy rice became increasingly delayed from 1992 to 2012. The duration of the growing season was prolonged, particularly for the grain-filling stage (GS3). The prolonged growing season was beneficial to productivity. For spring maize, the average precipitation during GS3 decreased at a rate of 27.46 mm/decade, and the annual accumulated temperature over 10°C increased at a rate of 31.07°C/ decade. Farmers initiatively adjusted crop cultivars and selected drought-resistant crops to cope with the challenges of drought.
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