In plant factories, the plant microclimate is affected by the control system, plant physiological activities and aerodynamic characteristics of leaves, which often leads to poor ventilation uniformity, suboptimal environmental conditions and inefficient air conditioning.  In this study, interlayer cool airflow (ILCA) was used to introduce room air into plants’ internal canopy through vent holes in cultivation boards and air layer between cultivation boards and nutrient solution surface (interlayer).  By using optimal operating parameters at a room temperature of 28°C, the ILCA system achieved similar cooling effects in the absence of a conventional air conditioning system and achieved an energy saving of 50.8% while bringing about positive microclimate change in the interlayer and nutrient solution.  This resulted in significantly reduced root growth by 41.7% without a negative influence on lettuce crop yield.  Future development in this precise microclimate control method is predicted to replace the conventional cooling (air conditioning) systems for crop production in plant factories.

Light-emitting diodes (LEDs) have been widely applied in the controlled environment agriculture, which are characterized by relatively narrow-band spectra and energetical efficiency.  Most recently, the spectrum of Sunlike LEDs has been engineered and it closely resembles solar spectrum in the range of photosynthetic active radiation (PAR, 400–700 nm).  To investigate how plant growth responses to the spectrum of Sunlike LEDs, cucumber and lettuce plants were cultivated and their responses were compared with the conventional white LEDs as well as composite of red and blue LEDs (RB, R/B ratio was 9:1).  We observed that although Sunlike LEDs resulted in a longer stem in cucumber, dry weight and leaf area were similar as those under RB LEDs, and significantly higher than those under white LEDs.  Moreover, cucumber leaves grown under Sunlike and white LEDs showed higher photosynthetic capacity than those grown under RB LEDs.  For lettuce, plants grown under Sunlike LEDs showed larger leaf area and higher dry weight than the other two treatments.  However, the leaf photosynthetic capacity of lettuce grown under Sunlike LEDs was the lowest.  In this context, the spectrum induced plant functions are species-dependent.  Furthermore, the three types of LEDs show distinct light spectra and they are different in many aspects.  Therefore, it is difficult to attribute the different plant responses to certain specific light spectra.  We conclude that plants grown under Sunlike LEDs exhibit larger leaf area, which may be due to some specific spectrum distributions (such as more far-red radiation), and consequently are favorable for light interception and therefore result in greater production.

 

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.