The Dark Respiration of Sugar-cane and the loss of Photosynthate during the Growth of a Crop

The dark respiration of the whole shoots (stems and leaves)and stems only of plants of commercial sugar-cane cultivars(Saccharum hybrids) of different ages was measured in a largerespiration chamber. The respiration rates of all parts of the plants were closelyrelated to ambient temperature. On a unit dry-weight basis leavesrespire faster than stalks at the same temperature. However,as the stalks grow and their dry weight increases with age andgreatly exceeds that of the leaves the greatest loss of carbohydrateby respiration occurs from the stalks. The percentage loss of gross photosynthate due to respirationhas been estimated for different stages of growth. The lossdepends on the age of the plant and the relative proportionsof leaf and stalk. It can range from some 20 per cent in activelygrowing young plants to at least 50 per cent in 18-month-oldplants of an irrigated crop in Natal.