Effects of Shading the First Leaf on Growth of Barley Plants: I. Long-term Experiments

Plants of barley were grown under controlled conditions andthe first or second leaves covered with tubular shades thusreducing the light intensity at the leaf surface to low levels.Expansion of the shaded leaves was not prevented, but appearanceof the next leaf but one and all subsequent leaves on the mainstemwas delayed by up to 3 days. Primordia of the first four leaveswere present in the dry grain. Shade treatment delayed slightlythe initiation of the eighth and subsequent leaves and transitionto the double ridge stage at the mainstem apex. Shading the first leaf caused a temporary reduction in the rateof dry-matter increase of plants, but after 14 days the ratewas similar to that of control plants. Smaller effects werefound when the second leaf was shaded. Dry-matter productionfollowed two logarithmic phases in the period prior to awn emergence,and rates for the whole plant and for plant parts were similarfor control and shaded plants. Thus, apart from the initialperturbation, shading had no effect on growth in terms of rateof dry-weight gain. Shade treatment did not affect weight per grain or numbers ofgrain per ear, but over-all yield of grain was significantlyreduced since shading delayed the appearance of tillers andalso reduced the number of tillers bearing grain. The effectof shade was especially marked on tillers originating on primarytillers. Similar qualitative effects on tiller development werefound in an experiment on wheat.