This study focused on the physiology, growth and antioxidant activity response of hydroponically grown lettuce (Lactuca sativa L.) under sole-source LED lighting of differing spectra. Lighting spectra were provided by differing combinations of LEDs of three different peak wavelengths, (Blue 435, Blue 450, and Red 663 nm) with ratios of B450/R663: 1.25 ± 0.1, B450/R663: 1.25 ± 0.1, and B450/R663 1:1 at two light intensities of photosynthetically active radiation (PAR) (270 μmol m−2 s−1 and 60 μmol m−2 s−1). A further experiment was conducted, in which Blue and Red LEDs were supplemented with Green (Blue 450, Red 663, and Green 520 nm) with ratios of B435/R663: 1.25 ± 0.1, B450/R663/G520: 1/0.73/0.26, and B450/R663: 1.25 ± 0.1. LED light intensities under the different spectra were adjusted to deliver the same level of PAR (270 ± 20 μmol m−2 s−1). Results from the first experiment showed that increased fraction of blue 435 nm in combination with red light at 663 nm at high irradiance enhanced the physiology of lettuce (i.e., significantly increased assimilation rate, stomatal conductance and transpiration rate) and increased the yield while having no significant effect on antioxidant activity. At the lower irradiance, the B435/R663 significantly increased antioxidant activity compared to other spectra. Results from the second experiment showed no significant effect of the spectra of LEDs on the physiology and yield of lettuce, but antioxidant activity was very significantly induced by B450/R663 at the ratio of 1.25 ± 0.1. However, the amount was still less than that obtained by B435/R663 1.25 ± 0.1 from the first experiment. This study indicates that LED light with a spectrum of B435/R663 at a ratio of 1.25 ± 0.1 significantly improves lettuce yield and antioxidant activity.
International audienceOver the last two decades, the impact of elevated CO2 on crops has become a major issue in the context of climate change. Increasing CO2 levels should modify the plant demand for nutrients, but precise effects on plant physiology are poorly known. Here, we studied the effect of ambient CO2 at 400 μmol mol−1 and high CO2 at 1,000 μmol mol−1 on safflower (Carthamus tinctorius L.) at N levels from 25 to 175 kg ha−1. Growth and physiology of safflower were assessed in pots in controlled enclosure chambers in a glasshouse. Overall results show that high CO2 increased assimilation rate by +27 %, leaf area index (LAI) by +28 %, total above-ground dry weight by +51 %, and total above-ground dry weight by +43 % at harvest. High CO2 reduced stomatal conductance by −29 % and transpiration rate by −18 %. At anthesis, results show that high CO2 increases assimilation rate by +13 %, LAI by +2 %, and above-ground dry weight by +34 %. At anthesis, results also show that high CO2 decreases leaf N and chlorophyll content
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