Leaf Growth in Dactylis glomerate following Defoliation

Abstract

Defoliation to a height of 2.5 cm considerably reduced the increase in leaf area in young Dactylis glomerata (cocksfoot) plants compared with that of intact plants, the reduction in the rate of appearance of new leaves being relatively greater than the reduction in expansion of existing leaves. The growth of those expanding leaves which were cut during defoliation accounted for 94 per cent of the total increase in leaf area during the first four days after defoliation. In such a leaf, expanding cells were confined to a basal section which was well below the ligule of the enclosing fully expanded leaf. There was a positive relationship between rate of leaf expansion and total soluble carbohydrate content of the stubble when the carbohydrate content was varied by placing the plants in the dark, but not when it was varied by defoliation and subsequent growth. These and other results suggest that the concentration of soluble carbohydrate in the bases of expanding leaves was a factor controlling leaf expansion following defoliation, and that the concentration in any one leaf depended on the photosynthetic contribution from its exposed portion. When the external nutrient supply was high, removal of the laminae of fully expanded leaves, which comprised about two-thirds of the total leaf area, did not reduce leaf expansion. When the nutrient status was low, these leaves were of primary importance, presumably because of their role as a source of labile nutrients.