AARSLEV, DENMARKScientists know that plants can actually "sense" day length, and "schedule" their growth to coincide with specific environmental conditions. These natural events are based on the circadian clock, a 24-hour system found in most biochemical and physiological processes. Plants grow better in circadian conditions that correspond to natural environments, but until now researchers have not understood how plants' internal circadian clocks respond to irregular lighting environments such as those found in many greenhouses.
Greenhouses in northern latitudes rely heavily on supplemental light sources to extend the number of light hours during the day. To conserve electricity and lower costs, newer low-energy input systems use lights only during less expensive off-peak hours and turn lighting off during peak load periods in the afternoon and in the morning. These systems, though more cost-effective than conventional lighting methods, create irregular lighting patterns of natural sunlight interrupted with artificial lightinga challenge for both growers and plants.
Danish scientists Katrine Heinsvig Kjaer and Carl-Otto Ottosen from the Department of Horticulture at Aarhus University published a study in a recent issue of the Journal of the American Society for Horticultural Science that sheds light on the question of plants' response to interruptions in lighting cycles. "Circadian rhythms are believed to be of great importance to plant growth and performance under fluctuating climate conditions. However, it has not been known how plants with a functioning circadian clock respond to irregular light environments that disturb circadian-regulated parameters related to growth", they explained.
For their experiments, the team used 300 cuttings of chrysanthemum (Chrysanthemum morifolium 'Coral Charm') grown in 19 hours of light for 2 weeks. The plants were then randomly placed in either of two greenhouse compartments with
|Contact: Michael W. Neff|
American Society for Horticultural Science