Abstract
Experiments were conducted in controlled environment chambers to study the effects of daylength and light energy efficiency on leaf emergence and leaf growth of the main stem in barley plants. Plants were grown at constant daylengths between 6 to 24 h. The leaf number on the main stems was counted (in Haun units) every day from the emergence of the second leaf until the emergence of the seventh leaf. The area, length and dry weight were measured from the second to the sixth leaves on the main stems. The leaf emergence rate increased with the increase of daylength. But the leaf growth rate increased with the increase of daylength until an optimum daylength of 15 h and then declined under longer daylengths. The leaf emergence rate per irradiance hour was slower with the increase of daylength. The leaf growth rate per irradiance hour also decreased with the increase of daylength. The leaf emergence and leaf growth under different daylengths, but at the same light energy, were different. Both the optimum daylength for leaf emergence and for light energy efficiency to cause a barley leaf to emerge and that for leaf growth and for light energy efficiency to cause it to grow were different.
