Canopy Photosynthesis and Time-of-day Application of Supplemental Light

Abstract

<jats:p>There is increasing use of electricity for supplemental lighting in the northern European greenhouse industry. One reason for this may be to secure a high growth rate during low-light periods by an attempt to increase net photosynthesis. We wanted to clarify which period of the day resulted in the best use of a 5-h supplemental light period for photosynthesis and growth. The periods tested were supplemental light during the night, day, morning, and evening. The experiments were carried out in daylight climate chambers measuring canopy gas exchange. The air temperature was 25 °C and the CO<jats:sub>2</jats:sub> level ≈900 ppm. Vegetative chrysanthemum was used, because this species responds quickly to change in light level. The leaf areas of the plant canopies were nondestructively measured each week during the 4-week experimental period. The fact that the quantum yield of photosynthesis is greater at low than at high light intensities favors the use of supplemental light during the dark period, but growth measured as dry weight of the treated plants at the end of the experiments was not significantly different given identical light integrals of the treatments. However, one experiment indicated that increased time with dark hours during day and night (24 h) might decrease net photosynthesis. The assimilation per unit leaf area was approximately the same during times of sunlight through a diffusing screen at 100 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> of photosynthetic photon flux (<jats:italic>PPF</jats:italic>) as during times of supplemental (direct) light application at <jats:italic>PPF</jats:italic> of 200 μmol·m<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> by high-pressure sodium lamps. We conclude that during the winter and periods of low light intensities, the daily carbon gain does not depend on the time of supplemental light application, but is linked to the total light integral. However, extended time with dark hours during day and night (24 h) might be a disadvantage because of longer periods with dark respiration and subsequent loss of carbon. Our results indicate that during times of low light conditions, it is not necessary to include factors such as the timing of supplemental lighting application to achieve higher net photosynthesis in climate control strategies.</jats:p>

Growth of Chrysanthemum in Response to Supplemental Light Provided by Irregular Light Breaks during the Night

“…Protected plant production systems at northern latitudes largely rely on the use of supplemental light to extend the number of light hours during the day and subsequently the light integral (Markvart et al, 2009). However, because the electricity prices vary on an hourly basis, an economical optimization of supplemental light depends both on the photosynthetic efficiency of the light and on the cost of the light.…”

“…However, because the electricity prices vary on an hourly basis, an economical optimization of supplemental light depends both on the photosynthetic efficiency of the light and on the cost of the light. In a recently developed low-energy input system for optimal use of supplemental light, it was recommended that light should be turned on only when energy prices are low and turned off in peak load periods in the afternoon and in the morning (Markvart et al, 2009). Consequently, the daily light hours did not occur consecutively, but were instead split into periods of solar irradiance potentially combined with supplemental light during the day and a night period interrupted by irregular light breaks (NB lighting).…”

“…Long-day (LD) treatments in which the day was extended by supplemental light frequently promoted an increase in plant dry weight (DW) in comparison with plants grown in short days, even when the light integral was the same (Adams and Langton, 2005). Furthermore, total plant DW and overall photosynthesis were the same irrespective of the LD given as an extension of the day or by NB lighting (Aung and Austin, 1971;Markvart et al, 2009). In other studies, NB lighting proved to be less effective in improving plant growth than LD conditions obtained by extending the light period with supplemental light (Hurd, 1973;Langton et al, 2003;Tafazoli and Vince-Prue, 1978).…”

Photosynthetic changes in Cymbidium orchids grown under different intensities of night interruption lighting

“…SD with long dark period is disadvantageous in growth of LD plants because of high level of carbon loss due to short period of photosynthesis and long period of dark respiration (Markvart et al, 2009). Thus, DE or NI can be used in LD plants to increase A n and subsequent plant growth with promotion of flowering.…”

“…In Petunia and Impatiens, for example, plants grown under daylight for 8 h with supplemental lighting at 4 mol m −2 s −1 PPF for 8 h significantly promoted their growth through increased A n (Adams et al, 2008). However, a small increase in daily light integral by NI at low light intensity such as 3-5 mol m −2 s −1 PPF has often been ignored with respect to A n due to negligible effect on subsequent growth promotion (Adams et al, 2008;Markvart et al, 2009;Park et al, 2013). In the cases of Pelargonium, Zinnia and Dianthus, artificial lighting at 3-5 mol m −2 s −1 PPF did not induce A n during NI (Park et al, 2013).…”