The Rate of Apparent Photosynthesis of Whole Sugarcane Plants

The rates of apparent photosynthesis of whole sugarcane plantswhich do not suffer from water stress are linearly related tothe rates of solar radiation on a horizontal surface up to intensitiesof at least 840 Wm^–2. This holds good over a wide rangeof leaf areas from 200 dm² for young plants to 700 dm² for olderplants, and for temperatures in the range 14–35 °C. The amount of CO₂ assimilated per unit area of ground coveredby the leaves, at any intensity of insolation up to 840 Wm^–2,is approximately constant for plants between 3 and 18 monthsold. Thus the assimilation of CO₂ by a crop of sugarcane is linearlyrelated to the intensity of the insolation and the area of groundcovered by green leaves. Very young plants (3 months old) consisting mainly of numerousyoung leaves have apparent photosynthetic rates per unit leafarea which are some 1.5 times those of older plants (7 to 8or 17 to 18 months old) which carry fewer but proportionatelymore mature leaves. Water stress, caused either by under- or over-watering, reducesapparent photosynthetic rates below normal levels. The extentand duration of the reduction depends on the degree of stress. The onset of and recovery from such stresses are illustrated.