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 large respiration chamber. The respiration rates of all parts of the plants were closely related to ambient temperature. On a unit dry-weight basis leaves respire faster than stalks at the same temperature. However, as the stalks grow and their dry weight increases with age and greatly exceeds that of the leaves the greatest loss of carbohydrate by respiration occurs from the stalks. The percentage loss of gross photosynthate due to respiration has been estimated for different stages of growth. The loss depends on the age of the plant and the relative proportions of leaf and stalk. It can range from some 20 per cent in actively growing young plants to at least 50 per cent in 18-month-old plants of an irrigated crop in Natal.